AMA | March 2022

AMA Questions March 2022

krathorlucca
After all this time I still don’t understand why people choose to be bayesians when it comes to epistemology. For example, where does knowledge actually come from within a bayesian framework? And how does it deal with eniterely new ideas(i.e with no relation to any priors)

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If you take our observable world and retrodict without a past hypothesis, what are some concrete ways your retrodictions would look like the future and ways your retrodictions look like the real past? E.g. does ice melt, but the rotation of the Earth reverses? Do stars shine? Does the universe expand or contract?

Dan Pye
Given the fuzzy nature of the term emergence (strong and weak meaning almost the opposite of each other), do you think there could be room to somewhat expand the meaning of the much less used word consilience to capture what is usually meant by weak emergence? Understanding that it usually refers to agreement between academic disciplines, it has a strong overlap with agreement between levels of reality and reconciling different ways of speaking about the same reality.

Carlos Nunez
What's your view on the tradeoff between free speech and misinformation? Is it okay for platforms to restrict freedom of speech, if that has a considerable positive effect on social welfare?

Andrew Jaffe
In any of the Many Worlds, is there a better trade then the Harden for Simmons trade?:) what do you now think Sixers chances are of winning it all this year?

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Sandro Stucki
I'm amazed by the length and quality of the AMAs. The number of questions left here by patrons seems to just go up and up. Can you tell us about your process for making an AMA episode? How much time does it take you to select and edit the questions, to record them, to prepare the audio material for upload, etc?

Frank Lehman
In your AMA instructions, you explicitly note "I am not a huge fan of special-relativity puzzles and paradoxes." I'm curious -- what is it about these kinds of scenarios that you don't like fielding?
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Benjamin Zand
Does the coordinate system we chose for the metric in GR tell use something about the location of the observer? For example where is the observer in the original coordinate system (polar coordinate) used in the Schwarzschid metric?

Tara Lumaghi
Are there mathematical objections to super-determinism as opposed to just philosophical ones?

Brad Malt
How is it possible that we are able to observe the cosmic microwave background? It has had 13.4 billion years to travel to us, but with the expansion of space, aren’t we more than 13.4 billion light years away?

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Ken Wolfe
If the Simulation Hypothesis posits that we can never tell for certain that we are not in a simulation, then is an assertion that either we are or are not just a statement of faith? Is there anything that differentiates this from statements of theology?

Noble Gas
I was surprised by how seriously Chalmers, in his recent book, takes the idea that we are living in a simulation. To me, this idea seems to re-create theism from a technological standpoint. Do you see it this way as well? And as someone who has stood against theism, does the growing acceptance of the simulation idea in philosophy circles bother you?
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Marian Marcali
I was thinking how entropy is increasing but knowledge and complexity seems to be increasing in lockstep, as a function of the self referential nature of the universe. So, in computational terms, the universe and therefore humans can abstract anything to create new computational primitives or objects, ad infinitum. Goedel's and Turing’s observations can therefore be considered THE primary and most important feature and not a bug at all.

Deepthi Amarasuriya
If you could re-design the familiar format of the undergrad Physics curriculum, what changes would you implement in the content, delivery, and assessment?

Peter Behnam
Is there one of set of quantum fields to house all the many worlds or does each one have its own.

Jim Murphy
What’s your view on how pornography affects society, especially in its modern highly-accessible form? Do you see it as dangerous?

Saad Ahmed
Have you ever been taken by feelings of nationalism or patriotism in the past or now I suppose?

Justin Bailey
I used to see you quoted in New Scientist often for various cosmology related articles. How did you get on the list of scientists to call? Do reporters Just cold call you?

Scott Lewicki
Frequently in your episodes you will reference a previous Mindscape podcast guest when speaking to the current guest. There is often some great discussion that comes from this comparing or contrasting the views of more than one podcast guest. Have you considered inviting back two or more previous guests and creating a "panel" discussion that you could facilitate? If so, which guests would you bring together and what would be the theme?

Andrei Dinu
You explained in the past that the state of the Universe could be described by a vector in a Hilbert space. The evolution of the Universe is equivalent to the trajectory of this vector in the Hilbert space. However, the state of a system with a variable number of identical particles is described by a vector in a Fock space, which is the direct sum of several Hilbert spaces. How is this last space called and why do you not refer to THIS space when you think about the Universe as a whole?

Jonathan M Goodson
When you were a member of a World Science symposium on QM interpretations, the moderator asked the panel: Will the scientific community reach a consensus within the next 100 years? As I recall, the other participants said “yes” but when it was your turn, you opined that the consensus would be achieved within 50 years. Question: What was your thinking in giving that response? Was it anything more than confidence in MWI and the ultimate competency of your peers?

David Harrington
PRIORITY QUESTION: I have, since reading Lee Smolin's book on universes from black holes, been bugged by a simple question, a question that admittedly shows that I am stuck in Newtonian physics, but which also opens up a question for you in the many worlds interpretation -- where does the energy come from? In Smolin's hypothesis, a black hole of only a few solar masses would create a full-fledged universe (as would a black hole the size of those at galactic centers). Where does all of the extra energy come from?

Matt Rapoport
It occurs to me that the act of observing or measuring a particle requires hitting that particle with something like a photon and then having the photon bounce back into a detector. I'm wondering if the act of hitting the particle during an observation might change the particle's properties - such as its momentum. If you wanted to measure a particle's position with increasing accuracy you would want to use photons with smaller and smaller wave lengths and thus higher and higher energies. Is this a reasonable way for a lay person such as myself to understand the Heisenberg Uncertainty Principle?

Samuel Cohn
I've heard you mention that the Hilbert space of the universe is large but finite dimensional. How do you reconcile this with the commutator relation between the momentum and position operators? It's an elementary exercise that in a finite dimensional space, if the commutator of two operators is a multiple of the identity, then the commutator is 0.

Anonymous
Do you have any advice for casually talking about academic or "intellectual" interests and hobbies without coming across as bragging or trying to act superior? How would you describe The Middle Way between heavily editing yourself to make people comfortable, on one extreme, vs. refusing a responsibility to read the room on a basic level, on the other extreme?

James Maddox
In the Standard Model, what is a mixing angle? They seem to determine strength of interactions and relate closely to symmetry and unification, but do they have a physical interpretation?

Jake Macneal
Scott Aaronson suggested during a lecture I attended that quantum computing might be a useful method of teaching core concepts of quantum mechanics. Do you think that might be a good approach to introducing quantum mechanics, especially for those with more of a computer science background rather than a math and physics background?

anonymous
The collection of homeostatic chemical processes we call life self-propagate in the direction of the "arrow of time" because this is the direction where entropy increases. The "intelligent" computational systems based on these chemical processes we call our minds thus "experience" the "arrow of time". As a whole, the entropy in the universe increases, but there exists regions where entropy decreases. Could there be homeostatic chemical processes that propagate in the reverse direction in these regions? Life in the reverse direction?

Jim Watson
Regarding cosmic redshift (due to expanding spacetime), where does the energy loss from the photon go as it is redshifted?

Roo Phillips
David Chalmers refers to you in his new book, Reality+. He believes we are in a "pure" simulation. His credence comes from statistical analysis. If it is possible for someone in our universe to create a pure simulation, then it will be much more likely that we are sims because it is much easier to create billions of sim worlds than the universe to create billions of physical worlds with life. Where are your credences on these concepts and what, if anything, is Chalmers neglecting in his argument for us probably being sims?

Joe
Have you ever used Linux on a desktop/laptop or server? If so, what did you think of it?

Jeff B
As I listen to your interviews with guests, I'm always impressed by your ability to come up with questions that cut to the heart of a topic. Do you believe that this is something you are naturally talented at, or was it a skill that took practice?

Patrick Hall
You have spoken extensively on the importance of increasing interdisciplinary projects between philosophy and theoretical physics. What branch of philosophy do you think can benefit the most from collaborating with theoretical physics? Do you think the problems of metaphysics can be solved with theoretical physics?

Rob F
As a layperson, it seems strange to me that the square root of minus 1 is of such fundamental importance to quantum physics, and by extension, to nature. Can you help me understand why the imaginary number is of such importance; versus any other type of number?

anonymous
What are your thoughts on the current graduate student employment crisis? As an undergraduate student, I was blissfully unaware of the extreme number of steps one has to take and roadblocks that are in the way when one wants to work as a PhD scientist (5.5 years of grad school, most have to do a postdoc to find a job, and little to no control over final location). Does the academy have a responsibility to make prospective students aware of what they are likely walking into, even though it doesn’t benefit the academy? Are there any creative solutions you have thought of besides moving the bottleneck from “getting a job” to “getting into grad school”?

Anonymous
Priority question! (My first)
Would it be possible to calculate the minimum size the universe would have to be, assuming its finite, to have all possible interactions take place?
This would be assuming all possible outcomes are realized in many worlds.

Sid Huff
On Quora recently, someone asked why gravity has been so difficult for scientists to reconcile with quantum theory. Victor Toth, a physicist who often responds to questions such as this, referred to “semi-classical gravity”. While he called semi-classical gravity “an ugly kludge”, he also noted that “in all regimes accessible to us, semi-classical gravity provides answers that agree with experiment.”
What exactly is semi-classical gravity? Is it a step forward toward solving the problem of quantum gravity?

Cooper
I have heard David Chalmers and other proponents of the hard problem of consciousness completely dismiss emergence as a viable answer to consciousness. In fact, this dismissal appears to be one of their primary arguments against physicalism. However, it’s not as if we have finished the work to comprehensively describe every step in the emergent ladder between QFT and, say, a chair. And yet I don’t hear philosophers fretting about what its like to be a chair. Do you think there is a hypocrisy here in philosophers’ attitudes towards emergence? It feels arrogant and anthropocentric to insist that consciousness is special, but not other phenomena for which we haven't completely mapped out the emergent steps.

Jimi Sommer
Does intuition tell you that the universe began with the big bang, or some eternal cyclic model? It seems in the former, the universe has to come from nothing, and in the latter the universe doesn't have to "come" at all, but only because it was always here. Should one seem more likely than the other? Do our intuitions even mean anything when it comes to these kind of questions?

Dan O'Neill
As a physicalist, how do you explain suicide? Having lost a close family member to suicide, I find it hard not to think of it in dualist, nondeterministic terms: as an incorporeal mind _choosing_ to destroy its own body.

Casey Mahone
What are your thoughts on euthanasia?

anonymous
We have alot of information from history & a lot of smart people on the planet. Why is it that we can't get these smart folks to figure out a solution to what is going on in Ukraine?
Smart folks found a decent vaccine for covid19, why can't we just put an end to war?

Russell Wolf
Last month you answered a question from Pablos Papagiorgiu about having multiple conceptually different models of physics, and mentioned the possibility that the ultimate theory might include multiple models that each have different domains of applicability. As you were describing that, I started to wonder if quantum mechanics and relativity are an example of this scenario, because they use very different languate but agree in the classical limit. But then you finished by saying that we're nowhere near this becoming a realistic question to ask about. So what's the difference between the hypothetical you were describing and the situation in physics today?

Liam McCarty
My understanding is that an “interpretation” of a theory is so called because it doesn’t imply any difference in experimental results compared to any other interpretation. If so, I'm curious how you pick one over the others. Is it based on an Occam's razor type argument for simplicty? Do you use such an argument to advocate for the many worlds intepretation of quantum mechanics?

Kevin O'Toole
Whenever I hear the term decoherence in quantum physics, I can't help but think... it's named backwards! If an electron starts in a state totally uncorrelated with anything else, then evolves into a state where it's highly correlated with many other particles, the latter seems distinctly *more* coherent. A measured particle seems *more* coherent than an unmeasured particle.
In what sense is it intuitive to think of "decoherence" as "a process of becoming less coherent"?

P Walder
Within discussions around the concept of panpsychism the nature of matter is frequently queried. In particular Philip Goff suggests that physics at a fundamental level only describes what matter ‘does’ and not what matter ‘is’. Can you give an explanation of what matter ‘is’? Thank you

Mishi Stern
I recently heard your interview with Daniel Dennett. You discuss the manifest and scientific image.
My question: as the years go by do the things in the realm of the scientific image move to the realm of the manifest image?
What was once considered essential, becomes a useful superficial description. From molecules to atoms to neutrons/protons/electrons to quarks and leptons etc.

Napoleon's Corporal
I recently read somewhere the Bell's theorem has been called 'the most profound discovery of science.' One of your strengths is explaining challenging concepts so that they are understandable to non-scientists; would you explain the details of the test / experiment that supposedly proves the violation of locality, your opinion of the test and result, and how that fits into the Many Worlds concept?

Perry Romanowski
I often tell people that if you rewound time, all the things that happened would still happen the same way. Recently, a friend pushed back and said it wasn't correct because of Heisenberg's Uncertainty Principle. I think that is a misunderstanding of the uncertainty principle. Which of us is correct? If we rewound some set amount of time would all the same things happen?

Tim Ryan
How is the bass playing going? Have you explored any music theory? It can be very fun and rewarding.

Tom
I really enjoyed the Arvid Ågren episode on the gene's eye view of evolution. In your experience, does the "I would die for 2 brothers or 8 cousins" rubric has explanatory value for how people treat others in the world? E.g. is the lower degree of genetic overlap a primary explanation for the West historically devotes fewer resources to sub-Saharan Africa than to other Eurasian populations?

Paul Torek
Gary Marcus said that for an AI to have common sense, it needs certain mental faculties we have, including - to quote him - "a cost benefit system, which I think is innate". You seemed to agree, or at least not object. Yet in your May AMA, you questioned the idea that an AI will have values. You were replying to a question about Stuart Russell's argument, that AI presents an "alignment problem" because the AI's values might not align with ours. Have you changed your mind about whether an artificial general intelligence will probably have values?

Razi Ahmed
Why is Shcrodinger's equation constructed such that it only has a time derivative? If time and space are essentially the same (coordinates) why single out one coordinate.

Nicholas Walker
when is the book out based on the Biggest Ideas and will it be e-reader friendly ?

Claudio
I thought I had an understanding of the cause of the Hawking's Radiation from black holes. However, lately I heard some conflicting versions that made me realize that my version (pairs of particles popping out into space, one of them falls into the black hole and the other flies in the other direction) is pure BS. Can you give us an updated, no-clickbait explanation for the origin of the HR?

Matt Hickman
What do you think the odds are there's an extinction level event for humanity in the next 100 years? Do you think we're doing more or less enough to prevent such a thing, or should we be doing more?

Eric Chen
What is the largest cardinality of infinity used in modern physics? Do infinite sets with cardinality greater than that of the real numbers have any use in physics?

Pete Faulkner
Listening to your Wondrium course on Time and heard you talk about CPLEAR and the demonstration of time asymmetry in the weak force. Could this time asymmetry in some way be an explanation of the matter/antimatter asymmetry we see in the universe (in the sense that the CPLEAR experiment showed a small asymmetry between K decay and anti-K decay)?

Oleg Ruvinsky
You mentioned in the past that you love Iain M. Banks The Culture series.
Which are your favorites in it and why?

Rob Greyber
You recently had two podcast guests who talked about language - specifically, the mathematics and analytics underneath human vocabulary, language and stories, #174 with Tai-Danae Bradley and #181 with Peter Dodds.
Listening to both episodes, it seems Bradley laid out a theoretical exploration of language (is it possible to understand words and language by studying their context) and Dodds does a sort of "experimentalist" application of that approach (looks at ways to categorize stories to discern patterns).
I'd be curious to hear your thoughts on this field of study generally. Is this analytical study of language and stories just a descriptive exercise about an emergent aspect of our culture, or does it have some power to help us understand what deeper general AI, for example, might look like?

Phil
Is there a deeper reason why quantization works so well? Why would replacing classical observables with operators give such good results (or maybe I should ask this the other way around since QM is more fundamental).

Volaire oh
Bit of a dark question but would you rather survive a nuclear exchange, or be amongst the first to go?

Robert Ruxandrescu
In my system of values (in my moral system) I think everything is acceptable as long as no sufferring is brought by that action - sufferring is what gives an act its moral worthiness.
However, using this framework brings me to very taboo situations for most people, like the situation where a pedophile is satisfying his or her sexual fantasies doing a videochat with a parent who bathes their baby, let's say - the parent gets the money, the pedophile gets sexual satisfaction without hurting anybody and the baby is just completely unaware of anything like this happening.
In my own system of values this whole situation is not immoral. I've been trying to analyse if I'm making a mistake anywhere but I don't see anything "wrong" with it, however most people would be appalled at my conclusion and think I'm insane.
Do you see anything wrong, here? Any argument that I could use to come up with the conclusion that this situation is wrong?

Steve Pilling
what do you think of the black hole as fuzz ball or ball of string model. It seems to avoid problematic issues with the singularity where Sir Prof Roger Renrose says that space and time come to an end?

Ezra Parzybok
What are your thoughts on 'Preppers' or prepping for disaster, personally.

Holographic Cosmology
Priority question: We use two eyes to focus on one object’s position to create the illusion of depth. We didn’t always have this ability, it had to evolve. Is it possible that we’re looking at space wrong? Could we be missing depth, or other information, that we’d need two or more eyes capable of looking in two different positions at once in order to find?

Louis B.
Following up on the previous answers regarding falsifiability as a criterion for science. In a "beyond falsifiability" worldview, where does the hypothesis of a supernatural god fit philosophically? I know you consider it a "bad" hypothesis, but is it a scientific one? The supernatural, and gods, are typically dispensed with as non-scientific because they are non-falsifiable but it would seem you don't have this luxury. Is positing a god somehow less scientific than hypothesizing what is beyond the edge of the observable universe, or inside a blackhole?

Kathi Seeger
Michael Dine wrote (in his new book) about Weinberg's weak anthropic principle: "Just to explain the cosmological constant would require an absurd number of different universes, 10 to the power of 120 at least, but far more if other constants of nature are fixed this way." And he wrote: "Such a mode for explaining the world around us is just too much to swallow."
Would you, as a person not shy of invoking a huge amount of worlds in QM context, be as hesitant as Dine regarding the multiverse?

Anita Tomasik
Does state of thermodynamic equilibrium of the universe, in which time’s arrow no longer exists, affects in any way four dimensional structure of space time? I doubt it, but I wonder how it looks like, highly hypothetically, from “god-like point of view” perspective of the block universe?

Herbert Berkowitz
I recently saw a reference to a particle called the “anti-neutrino.” That stopped me in my tracks. How can a particle with no charge possibly have an “anti” particle that will obliviate it?

Peter A Bamber
I understand that in general relativity time is not absolute, that the passage of time at different points in space varies because of mass-energy densities between and around the points. I’ve also heard it said that in quantum mechanics time is a fixed backdrop along which wave functions evolve. Are these views incompatible and if so is this one of the reasons why GR and QM are difficult to combine into a single theory?

David Boardman
Is there a way to describe what a low entropy universe at the time of the big bang “looks” like compared to a higher entropy situation?

Samuel Benjamin
I’ve noticed from your books and podcasts that you like to use the term “loosey-goosey”.
Please can I get a shout-out for my cats Lucy and Goose. They’re sisters who we’ve had since 8 weeks old - Lucy is a more conventional cat in her behaviour, whilst Goose is I think more like Ariel (she likes to lie in the bath after it’s drained, much like Ariel’s morning shower routine).
What are your thoughts on giving animals the same rights as humans? Do you think this would be sensible and/or practical?

Robert Henderson
My impression is that it's not necessary to get into quantum field theory when thinking about quantum theory's foundational questions, and that non-relativistic quantum mechanics is sufficient. Is that so? And if it is, can you say why, given that questions around locality and the nature and space and time seem to be relevant to interpretational questions.

Bogdan Vinatoru
Russia has never given up in the last 30 years, since the collapse of the USSR, in the hope that Europe should remain divided, even against its will. It seems to me more than a war against Ukraine, it is a war against the free world, perhaps the most difficult test for democracy. Is it possible for people to understand what a valuable gift it is and to make us truly appreciate and protect it, as never before?

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0:00:00.0 Sean Caroll: Hello everyone, and welcome to the March 2022, Ask Me Anything edition of the Mindscape Podcast, I'm your host, Sean Caroll. A little bit late coming out this month. Sorry, it's March 5th. I usually try to get it out by March... By the beginning of the month, but things have been hectic, things are probably gonna be hectic again next month, lots of things I'm supposed to be doing other than doing AMAs, so we get... When we get it, there you go. For those of you who are listening, I don't know, far in the future or whatever, the world is in bad shape at the moment. We, in the last couple of weeks, have had the Russian invasion of Ukraine, which is intrinsically bad, the plucky Ukrainians are fighting back as best they can. NATO and the US, are trying to help them in various different ways without actually getting into a shooting war with Russia, which could lead to World War III. That's where we are right now in the world. I don't have a lot of wisdom about that particular conflict, although it's easy after the fact, of course, to say, Well, we should have done a lot more before the conflict started, to prevent it from happening in the first place, the West does have the ability to put economic squeeze on Russia in order to prevent it from doing things like that, but we didn't.

0:01:16.1 SC: And international cooperation is not always easy, and it's certainly never fast, but of course, this invasion has brought a whole bunch of countries together on the other side in ways that were unanticipated, so I guess there's a tiny little silver lining. Everyone knows everyone in the current era here, listening to the news, etcetera, has just enormous respect and admiration for the people of Ukraine who are fighting to keep their homeland and not be part of the Russian dictatorship. And it's heartbreaking 'cause it's very, very plausible, I would say that it won't work. Maybe it works, I certainly hope that they're able to maintain their sovereignty, but they're a tiny country against a big country, and so who knows? And so I'm not optimistic about that, but I keep my fingers crossed. And there's of course a whole bunch of other things going on in the world, politicians are doing stupid things as usual. We still have a pandemic that we're going through.

0:02:18.3 SC: Yeah. It's tough to keep your eyes on the positive aspects of things. I just put up a tweet with a picture of Arial just to cheer people up a little bit. That's the best I can do. I can offer kitty pictures. But I'm actually a believer that even in very, very trying times, and I should say needless to say, these times are not nearly as trying for me or for Americans more generally as they are for other people throughout the world, so a bit of empathy there. I'm not trying to make it as if my personal situation is all that bad compared to that of others, but it is actually important, I think, to not become too monomaniacal about these things, especially when these things involve world events that you or I individually had very little control over. Life is complicated and rich and multifaceted, and there will be bad things going on and good things at the same time, I don't think it's a mistake to acknowledge both. So just because terrible things are happening, it's okay to remember that there are some good things happening and vice versa, even if things are going very well, it's important to keep in mind that things aren't going well for everybody, and they could be better and working to make them better.

0:03:37.5 SC: So this is a very long winded way of saying, I think it's okay to have an Ask Me Anything episode of The Mindscape Podcast even when the world is falling apart, the world doesn't stop, it doesn't just come to a halt even when bad things are happening. And it's important to sort of keep our chins up and think about big questions that have an eternal aspect to them, as well as the pressing questions of the moment, we can do both, that's the point, we should be able to multi-task on this. So as always, if you aren't a regular listener here, this is the Ask Me Anything episode for Mindscape, we do this once a month, except for the end of the year. And the questions are asked by supporters of Mindscape on Patreon. So if you would like to be a supporter, you can go to patreon.com/seanmcarroll and pledge your support to this little project that we have going on here. And you get to ask a question. Back in the days when we were a wee plucky podcast, everyone who asked a question, we get it answered, these days there are too many questions. Sorry about that.

0:04:43.5 SC: But I try to answer the questions that I think I have something interesting to say about, as usual, every single month, there's more and more really, really good questions that I don't get to answer, so my heart breaks. I would like to be able to answer all the questions, but there's lots of things I'd like to be able to do that I can't quite get done. There you go, that's the world, the constraints of reality and time and space and energy and effort and ability, you gotta deal with them. And with that, but that not completely optimistic conclusion, let' go.

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0:05:28.4 SC: Krete Luca says, "After all this time, I still don't understand why people chose to be Bayesians when it comes to a epistemology. For example, where does knowledge actually come from within a Bayesian framework, and how does it deal with entirely new ideas, I.e., with no relation to any priors." Well, I think, as I said before, you have to separate out two different things, one is Bayes' theorem. And Bayes' theorem is a is a theorem, it's just right. No one is allowed to disagree with it unless you disagree with basic facts about math and logic. And Bayes' theorem says that when we have some credences and some propositions and then new evidence comes to bear, here is a formula that tells you how you change your credences. So you're sort of not allowed to disagree with that formula if you accept the basic axioms.

0:06:13.3 SC: But Bayesian epistemology or Bayesian inference or whatever you wanna call it, is a slightly more broad scope kind of set of claims where you're saying that, that is the way that we should think about gaining new knowledge, you always start with some credences and you always update them. Now there's many, many details that are worth trying to get into here. Like when I say new knowledge, new data, what counts as new data? Is it literally new facts about the world that we've been empirically measuring, or can a new insight count as new data in some sense. And I think that the clear answer is, Yes, new insight definitely counts as new data. If you realize that your proposition is actually predicting something that is true, even though you didn't originally realize that, then that should increase your likelihood in that particular... Your credence, if you like, in that particular proposition.

0:07:09.9 SC: So the question I take it is that the usual... Maybe I'm not sure Krete Luka if I am force feeding or forcing your question into a framework that I understand, but the usual question is about the priors. So a Bayesian starts with prior credences, you have to start somewhere. And then you update them and everyone agrees on the updating the priors are sort of philosophically difficult. Where do they come from? I take it that is the basic question here...

0:07:42.4 SC: Yeah. So they come from human beings inventing priors, as I joked, I forget whether it was in the big picture or one of my other books, everyone is entitled to their own priors, no one is entitled to their own likelihoods. The likelihoods are the functions that tell you the likelihood of getting certain data given some proposition being true. But everyone's entitled to their own prior. So where do they come from? They come from the fact that we are human beings embedded in the world, our brains are not blank slates, we have models of the world, we have the manifest image, we believe in three dimensions of space around us and gravity and all sorts of things like that, continuity over time, of various course features of the world, and that brain, as part of the physical universe has opinions, it just has opinions, whether you like it or not. Even if you give somebody a proposition that they have never contemplated before, they can come up with a prior on whether that they think that proposition is true or not. Different people will have different priors, the hope is that they can collect enough data so that their priors go away.

0:08:49.2 SC: That's always the hope of Bayesian epistemology, which is a fancy way of saying that we do science to the world, that's how we make progress. We gather data, and it doesn't matter what our initial opinions were, if those opinions become flagrantly in conflict with the data, we get rid of them. So philosophically, you might not like that idea that our brains come up with these priors in different ways, in fundamentally subjective ways, I just think that that's it. There's no better way to do it than that. There's no out there in the world objective handle that we have. I think that this is part of my own intellectual journey. I was a person so many years ago who was as foundationalist as anybody who really thought that we should go looking for absolutely solid grounding for all of our beliefs, including beliefs about morals and aesthetics and so forth.

0:09:45.0 SC: And the more and more I think about it, the more and more I read, the more and more I exist in the world and try to make sense of it, the more subjective, I believe that some things are. The physical world is not subjective, there's a real honest world out there. But when you say, "Okay, how do these little agents called human beings develop knowledge about the world?" There's gonna be a necessarily subjective feature there, there's not a rock-hard foundation on which to build an unbreakable edifice of pure knowledge, maybe we'd like that to be true, but I don't think it is.

0:10:15.0 SC: Anonymous says, "If you take our observable world and retrodict without a past hypothesis, what are some concrete ways your retrodiction would look like the future, in ways you retrodiction would look like the real past. I eat as I smelled but the rotation of the Earth reverses, do stars shine, etcetera." Okay, so the set up for this question is the arrow of time question, we think that entropy is increasing towards the future for two reasons. One is because starting from today, we start with some coarse grained information about the world. We don't know the microstate of the world, we don't know every atom and molecule and what they're doing, but we know some coarse observable features of it, and we have a probability distribution of what the micro-states could be doing within that macroscopic set of constraints.

0:11:02.5 SC: And so you can from that predict the future in some probabilistic way, okay? Now you could also try to predict the past, but in fact, what we actually think happened in the past is utterly different than what you would get just on the basis of predicting from the current macrostate. We think the entropy of the universe was lower in the past, and so we assumed that the early universe started with very, very low entropy, that's the past hypothesis. And then we condition-lize on that, when we make predictions, if you will, about the past. We don't just say, starting with our current information. We say, starting with our current information and the hypothesis that the past had very low entropy, what do we reconstruct about the past? And this is so ingrained in how we think that it is very difficult to break out of just assuming that past hypothesis. And so in particular, if you didn't have it, this is the question asked by Anonymous, if you didn't have the past hypothesis. If you only had information about the current macrostate of the world, what would you predict about the past and future? And the important thing here is this division of knowledge into micro states and macro states. So the Earth going around the Sun has a macrostate, and let's imagine that that macrostate is just defined by the center of mass of the Earth where it's located, how it's moving and maybe it's rotation or something like that, it's already...

0:12:24.8 SC: You're already noticing that the level of coarse graining is important for some people, astronomers, it's usually okay, you just treat the Earth as a point going around the sun. For geologists, it's not good enough, you need to take care of all the mountains and oceans and things like that, but we're being astronomers right now. Okay? So that... There's is a macrostate because we're ignoring details of what all the molecules and the particles in the Earth are doing.

0:12:49.5 SC: And when you say, I take the current macrostate and evolve it backward in time without a past hypothesis, what happens is to evolve backward in time, you just imagine reversing the momentum. Right? Reversing the momentum of every object and evolving it forward in time is the same... Gets you the same kind of answer as just evolving backward in time. So for imagination purposes, it's useful to think about reversing the momentum and that macrostate of the Earth has a momentum. It is moving around the sun, the center of mass of the Earth. And so that would reverse. So that's just a fancy way of saying that if the Earth is moving around in a certain direction toward the future, it would still move backward toward the past. The Earth moving around the sun is a physical system that has very small numbers of moving parts to the Earth and the Sun, as long as you can ignore some very, very tiny title effects and out gassing and things like that, and it's very, very predictable. There's no entropy increase or decrease as the Earth goes around the Sun, there's entropy increase or decrease because of radiation and things, but we're ignoring that for right now.

0:13:56.7 SC: So you can easily retrodict the Earth going backward. That's no problem at all. You've reversed that momentum. What you don't do is reverse all the microscopic momenta, you're not allowed to do that, 'cause you don't know what they are, 'cause you only know the current macrostate. So roughly speaking, if all you knew is the current macrostate, if you wanna know what you predict for the past, it is exactly the same as what you predict for the future. Okay? Except for these macroscopic momenta being reversed. So in particular, you predict that toward the future, the sun is shining. What does that mean? That means that there is radiation that is leaving the sun and escaping to infinity, escaping to distant space. So if you had a little meter that was counting the flux of electromagnetic radiation, you would get a lot of flux going from the direction of the sun out into the opposite direction. If you retrodict the past without a past hypothesis, you predict the opposite of that, which is you predict radiation flowing from the sun into the past, if that makes sense. It's equivalent to saying You predict radiation coming toward of the sun.

0:15:08.7 SC: Okay? If you had a little meter there in the past, it would detect a strong amount of radiation coming toward the sun from empty space. And you say to yourself, "Why in the world... How does it know? How does that radiation know to go towards the sun?" But the point is without the past hypothesis, the current moment in the history of the universe is very, very special. We do not live in thermal equilibrium, we are in a relatively low entropy state compared to thermal equilibrium. So that's why entropy can still increase toward the past, but without the past hypothesis, entropy also... Sorry, I said increased toward the past, I meant, that's why entropy does increase toward the future starting from now, without the past hypothesis, it would also increase toward the past in exactly the same way. So the reason why this radiation focusing in on the sun, knows to do that is because the sun right now is in a very special low entropy state, all things considered, if you don't think that there was an even lower entropy state before that. Of course this seems weird because we have an intuitive feeling about how cause and effect works, and the arrow of time is built into that, but you've erased the arrow of time toward the past by saying, we have no past hypothesis, so you're gonna get some weird behavior.

0:16:30.0 SC: Dan Pi says, "Given the fuzzy nature of the term emergence, strong, weak meaning almost the opposite of each other, do you think there could be room to somewhat expand the meaning of the much less used word consilience to capture what is usually meant by weak emergence? Understanding that it usually refers to agreement between academic disciplines, it has a strong overlap with agreement between levels of reality and reconciling different ways of speaking about the same reality." I think that consilience is related and a fine thing to think about it, but it's not the same, it doesn't capture the same meaning as weak emergence because consilience would be completely possible if there were no higher levels. It's compatible with the idea that there's just one level that you can talk about. The statement of weak emergence is the statement that there are additional patterns that we can sort of grasp and make predictions using using only macroscopic information.

0:17:24.2 SC: Right? You don't need, in the example we just gave, to know all the details about all the particles in the Earth to predict how it is going to revolve around the sun, and that is an example of weak emergence. Of course, ex post facto, there is consilience with thinking about the Earth as a point with its center of mass versus thinking of the Earth as 10 to the 50th atoms and molecules, but there's an extra fact that is conveyed when you say there is a weekly emergent higher level description. So I don't think that it's a good substitute for that kind of vocabulary.

0:17:56.5 SC: Carlos Nunez says, "What's your view on the trade-off between free speech and misinformation. Is it okay for platforms to restrict freedom of speech, if that has a considerable positive effect on social welfare?" It's hard to answer these questions. They are important questions, but it's hard to answer in the abstract, I think it's... There's a temptation, similar to what I just talked about a second ago, there's a temptation to find a simple rule and just apply it absolutely, and unthinkingly once you've made up the rule. But the real world is a little messier and more complicated than that. I mean, if you take this question at face value, is it okay for platforms to restrict freedom of speech? Platforms can't restrict freedom of speech, they can only restrict what you do on that platform. Right?

0:18:38.3 SC: Freedom of speech was never supposed to be the freedom to say whatever you want on any platform you chose. No one ever had the right to say, "I would like to print something on the front page of The New York Times." The New York Times has some legal obligation to print it. Okay? There is a difference now than in the past, that we do have the technological capabilities to allow people, anyone to use a certain platform, but we never do allow anyone. There's always people who are banned from the platforms for misbehavior of one form or another, and that's perfectly legal and perfectly legitimate. So it would be nice in terms of simplicity and clarity to say, everyone can say whatever they want, but no one ever says that, nor should they say that.

0:19:25.1 SC: So you have to do the hard work. You have to do the hard work of saying, okay how do we balance the consideration of letting people have as much free speech as we can possibly get away with, with considerations of both social welfare and the rights of the people who make the platforms. Right? I mean, the true Libertarian response to this would be, make your own platform if you don't like it. And I don't think that's a completely convincing response either because... It's easy to say that it's hard to actually do it. There are lock-in effects, there are monopolies, there's a whole bunch of issues going on that we can't sweep under the table. But at face value, yes, it is okay for platforms to kick people off of them, if there are good reasons to do so. Now, clearly delineating, what are the good reasons, etcetera. That's hard work, and there's no way we're gonna make it anything other than hard work, we need to do that work.

0:20:19.3 SC: Andrew Jaffe says, "In any of the many-worlds, is there a better trade than the Harden for Simmons trade, what do you now think of the Sixers chances for winning it all this year." So those of you who do not follow basketball might not be aware of the epic trade that was made by former Mindscape guest, Daryl Morey, president of basketball operations for the Philadelphia 76ers. Ben Simmons one the Sixers, All-Star players became unhappy for various reasons that I will not go into demanded to be traded. And James Harden another All-Star player who was playing for the Brooklyn Nets and previously had played for Derry Mori in Houston, also became unhappy at the same time, and so the two teams traded their headaches for each other.

0:21:03.6 SC: And I think... I'm very biased as a Sixers fan, but I think the Sixers years came out of that trade great. I could not imagine it really working out better. I'm sad because we lost two really good other players in Seth Curry and Andre Drummond as well as a couple of draft picks, but James Harden and Joel Embiid and Tyrese Maxi are just perfect complements to each other. I do think that the Sixers years will have a learning curve, I don't think it's all gonna be... They're not gonna go undefeated, let's put it that way, between here and the play-offs, especially on the defensive end. I think on the offensive end, it's just gonna work perfectly, and that's something that I've never said about the Sixers since 1983. But we've really had a killer offensive scheme in place. But the early returns are that unsurprisingly to me, James Harden and Joel Embiid who are both All-Stars and basketball geniuses, work really well together, so optimistic. If we can stop other people from scoring we will go very far, so I do think... I actually think that the Sixers have a very good chance of winning it all this year.

0:22:11.8 SC: I think that the only team I would clearly put ahead of them is Phoenix, if they get Chris Paul back, then I think the Phoenix deserves to be the favorite team to win it all this year, but the Sixers are right up there.

0:22:25.6 SC: Okay, I'm gonna lump together, group together, two questions, one is by Sandro Stocky, who says, "I'm amazed by the length and quality of the Ask Me Anything episodes, the number of questions left here by Patreons... " Patrons. Is it Patreons. It's probably Patrons, I think, Sandro, you're correct. "Just seem to go up and up. Can you tell us about your process for making an AMA episode, how much time does it take you to select and edit the questions, to record them, to prepare the audio material for upload, etcetera." And then Frank Layman says, "In your AMA instructions, you explicitly note, I am not a huge fan of special relativity puzzles and paradoxes, I'm curious, what is it about these kinds of scenarios you don't like fielding?" Okay, so two questions, two meta questions about the AMA process itself.

0:23:10.3 SC: So thank you, Sandro. It's a good way to get your question chosen by first saying how amazing the podcast is, that's always a very... It's a strategy worth trying... Let's just put it that way. I think that I'm impressed by the quality of questions by both their variety, they're not the same things over and over again, and by the depth, it's a fun mix of different things. I like the trivial fun questions, and if I don't answer your trivial fun question, it's not because I'm trying to diss you or anything like that is just well I don't have a good fun answer to give you, that's all. So the process is we're getting, I don't know, between 100 and 200 questions per AMA each month. And so I cut and paste all of them from the Patreon post into a text file, and then I go through them all, and I just read them and decide which ones I have a possibility of saying anything interesting about and deleting the ones that I don't. And with a rough idea of how long the thing should be, I think that the long-term equilibrium here is between two and three hours for the length of these. I can't do three and a half or four hour AMAs every month. I just don't have it in me.

0:24:20.8 SC: But given that constraint, and so it does take some time to do that, it takes a few hours... The copy and pasting is easy, but reading them all, grouping questions that belong together, putting them in a sensible order, thinking about what my answers are gonna be that takes a few hours, then recording is pretty easy. Look, I'm not writing out answers, I'm just talking off the spur of the moment, given that I've answered... I've read the question ahead of time, but otherwise there's no preparation or anything like that. As I also say in the AMA instructions, I'm not gonna answer questions that involve me doing homework, so there's not that much extra effort, it's... The amount of time to record is the amount of... Is the length of the episode plus, I don't know, half an hour, you know, just for... 'Cause there will be some interruptions, the phone rings, whatever, I have to do a little bit of editing, noise reduction in Audacity and things like that, and then posting is another, I don't know, at most 20 minutes or something like that. So that I've gotten down to a science otherwise, I could not keep doing Mindscape on a regular basis if I didn't get the recording editing posting down to a pretty efficient system, then I would not be able to work very efficiently. So all in all, between recording and editing and things like that, and in choosing the questions, it's not a full day's work, but on that order, roughly speaking.

0:25:47.7 SC: Frank says, "What about special relativity puzzles, paradoxes why not?" Well, part of it is because there's not a lot of intellectual progress made in talking about special relativity, puzzles and paradoxes, I completely recognize that there's plenty of people out there who are not experts in special relativity and for whom these questions are endlessly fascinating. I get it, but I don't actually think of my own role or the parts of this role that I enjoy the most as being a physics a professor. I like being a physics professor, but I do that already. I want to move the frontier of knowledge forward, not just clean up the frontier of knowledge in the regime we're already in.

0:26:32.0 SC: So special relativity puzzles and paradoxes are not... It's not a real puzzle or a real paradox. It's just that we don't understand it because we're so used to speaking in ordinary pre-relativistic language of taking space and time as separate things. As soon as you say, I have a rod that is one meter long, boom, you're already not thinking relativistically, because real rods are not one-dimensional things, there are four-dimensional world volumes and you've already cheated by saying I have a rod one meter long. As soon as you start thinking in space time terms from the start, most of these special relativity puzzles and paradoxes just evaporate. And that's a journey we all gotta go on on our own. And it's just sort of a little redundant and not new and fun for me to go over that. This is not Quora or Reddit or something like that. This is not a, Let's solve our favorite physics puzzle kind of thing. I have immense respect and appreciation for that kind of activity, it's just not what I'm interested in doing here.

0:27:35.8 SC: Benjamin Zand says, "Does the coordinate system we choose for the metric in general relativity tell us something about the location of the observer. For example, where is the observer in the original coordinate system used in the Schwarzschild Metric?" No. Coordinate systems had nothing to do with observers. And again, this is something where I just talked about, the intellectual transition from Newtonian spacetime to special relativity. Here's the transition from special relativity to general relativity. In special relativity, it's called relativity because different observers measure different things, okay? And it's all okay, the real physical stuff is invariant, but different observers measure different amounts of elapsed time between different events and things like that. But there's still a very simple space time that you're in, Minkowski space there's a lot of symmetries.

0:28:25.1 SC: And so this idea that an observer can construct a coordinate system by sort of sending out signals all around and building a little system of rods and clocks is still perfectly valid in special relativity. In general relativity it's just not, you just generally can't do that. You can send out two light signals and they could intersect at some point in the future or whatever, or there's a great deal of arbitrariness in how you might imagine doing that. So it never was true, even in special relativity, even in Newtonian Mechanics, that there was some relationship between observers and coordinate systems. But for certain approximations in certain circumstances, it made sense to act as if it were true.

0:29:09.8 SC: So we're always talking about the reference frame associated with an observer and there's a kind of complicated construction that is in the back of your mind when you say that. In general activity, that's just no longer a useful thing. So we're more honest in general relativity, we just say You have a coordinate system and you also have maybe observers and they have nothing necessarily to do with each other, in particular, if there's multiple observers, they're all gonna be moving in different places in the coordinate system. So no, the origin of the coordinate system shouldn't in any way be associated with an observer in any particular relationship.

0:29:44.8 SC: Tara Lumaghi says, "Are there mathematical objections to super determinism as opposed to just philosophical ones?" So Tara, I'm gonna apologize ahead of time. I'm gonna use your question, not really to answer it, but to make a point. And the reason why I'm not gonna answer it is 'cause I don't know, I don't really know what the objections to super determinism are. Well, sorry, I don't know if there are mathematical ones in particular. There could be, so I imagine that what you would mean by that is that there is some inconsistency or some mathematical hurdle or objection you have to overcome to write down a fully coherent and consistent theory of super determinism, and maybe there's some obstacle to doing that.

0:30:32.3 SC: And the reason why I don't know, and I don't... I think it's okay for me not to know is I'm not really... And I don't pretend to be an expert in foundations of quantum mechanics as a field. That might sound weird because I write a lot of papers in the foundations of quantum mechanics, but my angle within that field is I think that the many-worlds interpretation is right. And I think that given that many-worlds interpretation is right, there's still lots of foundational questions left to be answered about probabilities and structure and all sorts of ontological and metaphysical and epistemological questions.

0:31:07.0 SC: So it's a full employment for a whole bunch of people to work in that field, but I'm not actually paying attention to the discussion around other interpretations of quantum mechanics or formulations thereof. And as I'm always very quick to say, this is a bet that I make, how to spend my time and it could be completely wrong, I could be wrong. I don't think I'm wrong, but it's very, very possible. I'm not being absolute or certain about it, but we always have to do this in any endeavor that involves spending time on something intellectual, trying to understand how things go, you have to take some things as, "Alright, I'm gonna assume this is right and I'm gonna build on that."

0:31:50.9 SC: If every single academic, whenever they did a research project started with zero assumptions, and I'm not... Tara, I'm not saying that you're saying anything like this, I'm just giving my background feeling about it, but you would never make any progress. Right? If you always said, "Well, let's not assume that we know what the foundations of quantum mechanics are." That's a perfectly valid thing. There are people who are experts really in the foundations of quantum mechanics as a field, and they can tell you the relative differences between the pros and cons of pilot wave theories and epistemic theories and many-worlds, and all these things, super determinism. I just... And I'm not spending time trying to do that.

0:32:33.0 SC: And I don't make assumptions about other things that other people think are perfectly settled. I think that inflationary cosmology might be right, but I don't think it's a 95% chance. I think that the chance that inflation is right is substantially less than the chance that many-worlds is right. Many other physicists would flip that and put it the other way around but there you go, that's it. You'll have different people with different opinions. That's how you make progress. So I don't really know the answer to your question, Tara, sorry about that. But I'm letting you know why I don't know it.

0:33:02.5 SC: Brad Malt says, "How is it possible that we were able to observe the cosmic microwave background? It has had 13.4 billion years to travel to us, but with the expansion of space aren't we more than 13.4 billion light years away?" So there's a simple answer to this and a complicated answer. The simple answer is, the cosmic microwave background doesn't come from some location in space, it comes from everywhere in space, it is what was happening everywhere in the universe, 380000 years after the Big Bang, the universe was re-combining the electrons and protons were joining back together. So from everywhere there was light being given off, there was radiation being given off. And so if you start today and trace light cones backward, it doesn't matter where we are, it doesn't matter how old the universe is you will always reach a point in the past that was glowing, okay, at the recombination surface at the surface of light scattering, and that will be sending light to us that we can observe.

0:34:02.6 SC: Okay, so that's the simple answer, but the reason why I wanna answer this question, is 'cause there is a more subtle thing here about we being more than 13.4 billion light years away, it's again, it's relevant to this question of our intuition, Newtonian versus special relativity versus general relativity. What does it mean when you say, we're more than 13.4 billion light years away, when you're in an expanding universe, okay?

0:34:26.9 SC: What they mean by that, people say that and it's true. And what they mean by it is if you could extend a line through a space-like surface of the universe, in other words, through a surface of constant time since the Big Bang, and you extended it out to the point where the thing that we see in the microwave background, that atom that we see emitting at the microwave background is now sitting, that distance along the space-like surface is more than 13.4 billion light years because the universe has been expanding. At the moment when the light was emitted that the analogous distance between where we would have been and where that atom was actually emitting is much less than 13.4 billion light years away. So that's because there's not really any good such thing as the distance between two different observers in an expanding universe. There's different distances that you can draw at different times, so you just have to not think that that quantity is important, you can measure it, you can define it... You can't even measure it. Sorry, you can't measure it, but you can calculate what it would be, but kinda who cares? So if you have some reason to do that, fine.

0:35:40.3 SC: But it's not a quantity that has any essential meaning to us, the distance between two points on the space-like surface defined in some particular way. Okay? What matters? And relativity are light cones. Those really exist. You can trace back the path of light and everyone agrees on that, that's not relative to some observer, some coordinate systems, some slicing of space, time or anything like that. And so the robust statement is starting from us here and now, trace backward in time on light cones, you will hit the surface of last scattering somewhere, that is the cosmic microwave background that we observe.

0:36:18.0 SC: When a group... Two questions together, one is from Ken Wolf who says, "If the simulation hypothesis posits that we can never tell for certain that we're not in a simulation, then is an assertion that either we are or not just a statement of faith. Is there anything that differentiates this from statements of theology? And the Noble Gas says, "I was surprised at how seriously Chalmers in his recent book takes the idea that we are living in a simulation. To me, this idea seems to recreate theism from a technological standpoint. Do you see it this way as well? And as someone who has stood against theism, does the growing acceptance of the simulation idea in philosophy circles bother you?"

0:36:53.7 SC: So for those of you who don't know, David Chalmers, former Mindscape guest, recently came out with a book, Reality Plus, where he really, really takes seriously the idea that we could be living in a simulation. And his major goal in that book to boil... It's a wonderful book, I very much encourage you buying it, he's really just a terrific writer, and this is the... Of all the books he's written, this is the one that is most aimed at a non-expert audience. It's still full of full strength philosophical arguments, but it doesn't assume a lot of the linguistic background that experts would have. So it's very, very readable. But his primary concern is not to argue that we do live in a simulation, but to ask, if we do, is what we're experiencing still real, right? And as a good poetic naturalist should do, I don't think he's a poetic naturalist, but he says, sure, it's real. It's as real as anything else. So that's his main philosophical point that he's trying to make. Okay.

0:37:50.9 SC: So both of these questions here from Ken and from Noble are saying, "Doesn't this smack of theism and the existence of God somehow." And amusingly, if you read the book, Chalmers says, "I'm a really good atheist, but this whole simulation argument thing has made me rethink that." Because in some sense, if we do the simulation, it is like having God, it's not the same kind of God as the traditional theological Christian God, but some higher being that actually wrote us up in their little computer simulation somehow.

0:38:25.7 SC: So look, I don't care if it is theological or not, I care if it's true. Right? And the same thing goes for theology. When you say that I am not theistic or I don't like theology, it's not that I sort of have objections to contemplating the possibility, it's that I have contemplated the possibility and I don't think the evidence supports that hypothesis. I'm perfectly happy with other people also contemplating the possibility, and also I could be wrong, new evidence could come in and convince me that I'm wrong. I think that I do... My hackles get raised a little bit whenever people compare a certain idea to theology as a way of dismissing it via by guilt, by association. Right? Don't tell me whether something is like theology, tell me if it's right or wrong. What is your argument for or against it?

0:39:21.9 SC: I once gave a talk, you can find it online, it's actually quite gotten quite a few views. I gave a talk in Oxford Conference on philosophy... Sorry, on cosmology and theology, I think. And so I gave the talk with a title, "God is not a good theory." And the whole point of the talk was to say that we can use all of the usual ways of evaluating scientific theories about the world to evaluate theism.

0:39:50.3 SC: But there was a typo in the conference program where my talk was entitled, "God is not a theory," rather than "God is not a good theory." So that ended up being the exact opposite of my point. My point is that theism, the simulation argument, the multiverse, many-worlds, all of these things, these are perfectly legitimate scientific ideas and you should judge them, okay? You should not dismiss them by using dirty words against them. Now, when it comes specifically to the simulation argument, I try to do this, I try to judge it as an argument, and I say... I try to be a good Bayesian, as I said before Bayesian epistemology. I try to say what would I expect the universe to look like if we lived in a simulation, and I try to compare it to what the universe looks like. And to me, the world that we observe around us, does not look like it would if we lived in a simulation. And this is the crucial Bayesian point, which is that it's not that we look at the world, and again, this works... This is exactly analogous to what you would say about theology, so in that case, the analogy is pretty good. It's not that you look at the world and say, can I explain this by positing the existence of God or positing the existence of a simulation.

0:41:10.0 SC: That's not the right move. The right move is to say, let's imagine that we are comparing our expectations from a purely naturalistic self-contained universe versus a theistic universe versus a simulation, what would I expect in each of those cases? So it's not sufficient to say, "I can explain the world, I want the theory to explain what I do see about the world." To say that, "Oh yes, this is exactly what I would have expected. And it's not what I would have expected." As I said before, the resolution in terms of pixels of our universe, as far as we know, it's infinite, we have no idea, but it's certainly really, really, really good, way, way better than it would need to be for any simulation. I see no reason why a simulator would want to cook up a universe like ours. That's not to say they couldn't, but if I'm being a good Bayesian, and what I'm supposed to ask is, "Is this what I expect?" And it is not.

0:42:05.2 SC: Marian McCauley says, "I was thinking how entropy is increasing, but knowledge and complexity seems to be increasing in lockstep as a function of the self-referential nature of the universe. So in computational terms, the universe and therefore humans can abstract anything to create new computational primitives or objects ad infinitum. Godel's and Turing's observations can therefore be considered the primary and most important feature and not a bug at all."

0:42:32.4 SC: So, I don't know, whether Godel's and Turing observations and for that matter, Tarski, I would throw him in there also. I don't know whether they should be features or bugs. They seem to be true facts about mathematical logic. And also I'm not quite sure when you say the universe and therefore humans can abstract anything to create new computational primitives ad infinitum. I'm not quite sure, I wanna go that far either, I mean, it's the ad infinitum that worries me there. I do think, and I've said this before, and I'm not an expert at it, so you shouldn't take my word for it. But I do believe that there is this kind of phase transition in reasoning, in cognitive capacity when a brain or an information processing system of some sort gains enough capacity to be a Turing machine, right? To run any sort of Turing available, computer program that you might wanna run, and as Turing showed, this is a lot of computation, essentially all the computations you would ever want to do. There are limitations on what such computations can do, like the halting problem, you cannot prove that a certain computer program will halt, etcetera, etcetera. But in the world of computations, there's a universality class that all computers of a certain strength can do all the computations.

0:43:50.1 SC: Now, there's still computations we can't do. That's why I'm a little bit averse to the ad infinitum at the end of your sentence, Marian, because we have finite resources in space and in time, and there's some computations that are literally impossible to do, like the halting problem, for example. So I think I know what you're saying, but I would just sort of edit that a little bit with the ad infinitum there. And the other thing that I'm not quite sure about is you say entropy is increasing, but knowledge and complexity seem to be increasing in lockstep. That I just think is not true. If I take a book and I burn it, entropy is increased, but knowledge is not increased, information, good old accessible information or complexity has not increased in any way. I think the reality is that entropy is increasing, complexity, information kinda come and go, right? There's pockets of them and they can disappear, and there's no law of nature that says that those things must increase in the same way that entropy is going to increase. So I think the relationship there is a little bit more delicate and nuanced and I think that it's a little bit too quick, a little bit too glib to just attach them to each other in some correspondence. We need to think harder about what the relationships are there.

0:45:06.2 SC: Deepthi Amarasuriya says, "If you could redesign the familiar format of the undergraduate physics curriculum, what changes would you implement in the content delivery and assessment?" You know, I don't have a great set of answers to this 'cause I have not been teaching undergraduate physics for a while. I taught one undergraduate course in the last 15 years, one quarter of one course, so one quarter in the sense of one term in the quarter system that we have at Caltech. So I'm not an expert in all of the details there. I have certain vague feelings. I do think that as it is with any curriculum, the curriculum in physics tends to lag behind the times a little bit, right? Usually, the curriculum that we teach now is what we really needed to be teaching 30 years ago, and not what we need to be teaching now or 30 years in the future. The obvious example here is how we teach quantum mechanics, and that's what's motivated me to think about writing a quantum mechanics textbook. Things like quantum information, decoherence, entanglement, quantum computing are not mentioned in a lot of undergraduate quantum textbooks, and there's no good reason for that, whereas we beat to death perturbation theory and Clebsch-Gordan coefficients and a whole bunch of things. So that one course, I think could be improved by quite a lot.

0:46:22.3 SC: The curriculum as a whole, I think that there's a lot of... Certainly, there's a lot of smart undergraduates who were zooming through the curriculum that I had when I was an undergraduate, so that they're like taking String Theory in their senior year or whatever, they've already taken quantum field theory in their junior year, which seems dizzyingly fast to me. There's no reason why general relativity should not be part of the undergraduate curriculum, maybe not as a required course, but I would like to see it at least be optional for everyone. I did introduce undergraduate GR course at University of Chicago, and that was very, very popular. It's a very, very accessible subject for undergraduates. There's no reason not to teach it. I think in the... The first year is always the crucial one, right? And I do... It kinda depresses me that the first year for many physics students has a kind of weed out the weak feeling to it, which I don't like, maybe there's a better way to do it than that. But honestly, I don't know what the better way is given constraints of resources and numbers and things like that, so I don't have any good suggestions there.

0:47:26.4 SC: I do wish that we could... Well, let me be specific about this. For physics majors, you have to just go through a lot of drudgery [chuckle] in the early days of your physics curriculum, right? You need to learn the inclined plane, and the electrical circuits, and that stuff, that is important. And so it takes time before you can get to the fun stuff of relativity and quantum mechanics and [0:47:48.8] ____, or what have you. So I don't think you should actually sort of put relativity or quantum mechanics in the first semester of your first undergraduate course, but maybe there is some way to get first-year undergraduates acquainted with some of the research being done in the department, whatever that is. Like little seminars or a one-credit course or something like that, and a lot of places do this. I just think it should be a regular thing. Let's make sure that people are excited by the prospects of doing this research themselves. For people who are not going to be physics majors, I think we do them a dramatic disservice by very often just offering them a course that is a watered-down version of the course we offer to physics majors, right?

0:48:36.9 SC: If you're not going to be a physics major, then why not learn a little about relativity and quantum mechanics? You don't need to learn about circuits and inclined planes necessarily, maybe a little bit of that is useful too, but I think that the purpose is completely different. If you're just trying to teach people physics for the sake of physics, rather than teaching them for the sake of a pre-requisite that will be useful when they get to other physics later on. I don't know. Those are not very coherent thoughts, but those are the thoughts that I have right now.

0:49:06.6 SC: Peter Benham says, "Is there one set of quantum fields to house all the many-worlds or does each one have its own?" I have no idea what the words to house mean [chuckle] in this case. Fields live in space-time, okay? Spacetime, and forget about quantum mechanics for a second, we have space-time and at every point in space-time, there's a set of fields. A value of the electron field and the gluon field and the gravitational field and so forth. In many-worlds, there's a set of worlds and each world has its own space-time and its own quantum field, so the fields are in the worlds, not the other way around. And space-time is in the worlds, not the other way around. That's why you can't say where other worlds are located. There is no space in which they exist. There's a separate question is whether or not it's the same set of fields in all of many-worlds? Let's put it this way. In the simplest versions of many-worlds without thinking too hard, it's exactly the same quantum fields and laws of physics in all the worlds. I do think it is possible to have slightly more sophisticated versions, but I don't think it's a necessary part of the theory.

0:50:19.3 SC: Jim Murphy says, "What's your view on how pornography affects society, especially in its modern, highly accessible form? Do you see it as dangerous?" Well, it's a tricky question. I mean, it's dangerous, but in the same way that many things are dangerous. So pornography is dangerous, in the same way, that driving cars is dangerous or drinking alcohol is dangerous. They can be misused and cause a lot of deaths. I think the number of deaths caused by cars and alcohol is probably way bigger than the number of deaths caused by pornography, and yet they are perfectly allowed and very easily accessible. I do think that and maybe... I'm not an expert on this, the psychology here, so I probably should say nothing. But my vague feeling is that there's some sense in which pornography can be addictive in a way that alcohol can be addictive. But again, that doesn't we ban alcohol, we just try to give people, number one, the freedom to choose and hope that they make the right choice. And number two, hope that they use it responsibly, and number three, some resources if they do get addicted to it. I wish that society did all those things anyway. It doesn't always measure up to those hopes, but that would be my hope.

0:51:27.9 SC: Do I see it as dangerous? It depends on what you mean by dangerous. I guess there's a danger, a potential danger in the sense that people sort of become immersed in pornography and lose the ability to connect with regular human beings in the same way. That doesn't sound like a huge worry to me, and even if it were, I still think that there is sort of an individual choice that I would err on the side of. But I'm not an expert, so maybe there's some deeper worry there that I don't know about. The other set of dangers, which has been well talked about is, of course, it gives people a sort of degraded image of women. When we talk about pornography, it's usually men looking at pornography of women, and that can have all sorts of effects on how they think about women more generally. And this was a bigger deal and it's something that was talked about a lot more, I guess, probably in the '80s than it is today, but it's still out there. And I think that this is a case where it would be important to separate the symptoms from the real problem. I think if we lived in a society where women were treated more equitably from the start, then you could very easily imagine non-deleterious forms of pornography, they'll be perfectly okay. In other words, I don't think it's the pornography, that is the trouble.

0:52:53.8 SC: It's that the problem is that the women are not treated equitably or thought of equitably in our society. That's the real fundamental problem. So I would not put a Band-aid on pornography and claim victory there, I think that's not really the way forward.

0:53:07.1 SC: Saad Ahmed says, "Have you ever been taken by feelings of nationalism or patriotism in the past or now, I suppose?" I guess, probably no is the short answer if I'm trying to guess what you mean by that. I mean, I might root for the Dream Team, [chuckle] US basketball team in the Olympics, when they were the Dream Team, back when Michael Jordan and Larry Bird and Magic Johnson were playing for them. These days, I don't care as much about the Olympics one way or the other, but sports and things like that are completely harmless or almost completely harmless versions of nationalism or patriotism. I think that the US is a big, complicated country with a big complicated history, and my version of patriotism is to both appreciate the good aspects of its current existence and its history, and very much appreciate its bad aspects as well. I am very much against whitewashing the bad aspects of our history. I think that teaching how horrible we have treated the rest of the world is really, really important. And I think that's part of the ability to do that, to the extent there is such an ability, is part of what makes a country strong.

0:54:26.4 SC: You should do that, and different countries have different success rates at doing that. I think the United States is kind of mediocre at that. The US does tend to perceive itself... The average American, if that's even a sensible concept, is way more sanguine about America doing bad things to the rest of the world than they should be either currently or in the past. But I can still appreciate the values that the United States was founded on, and by that I mean the sort of aspirational values, not the reality of what was going on back in the 18th century, 'cause that was obviously very messy and compromised. But I can accept that and at the same time think that the people who started up the United States were onto something good when they thought that the authority of a government comes from its people, not from God or from someone having more power than anybody else. We had a long road to... That is nowhere near finished yet to actually achieve that ideal, but I think that's a good thing. Something that's perfectly okay to be proud of. Realizing that we were not the first, we were not the best, but it is something we did right.

0:55:42.3 SC: So I'm not out there waving the flag or anything like that, but I think the nuanced view of the history of a country is an important thing. This is not the United States, so it's not quite apropos, but there's this wonderful meme that has gone around for years of how people in the UK view the UK and how people outside the UK view the UK and inside, it's like this cute little bulldog puppy, and outside it's like this terrible ravenous wolf. The United Kingdom, England, and Great Britain, they've invaded everywhere. And if you ask them, they're like, "Just bringing civilization everywhere. Shouldn't they be thankful?" I don't think that big powerful countries bringing civilization elsewhere has really been a successful from the point of view of the people whose civilization is apparently being imposed upon them as the imposers would like to believe. So this is all a very complicated stuff. I think that again, simplifying it is the one bad thing that you can... Over-simplifying it is the one big mistake you can make.

0:56:46.6 SC: Justin Bailey says, "I used to see you quoted in New Scientist often for various cosmology-related articles, how did you get on the list of scientists to call? Do reporters just cold call you? Yeah, there's no magic bullet or a special procedure to get called by reporters. It depends on the situation, and it usually sort of accumulates over time. Sometimes you meet reporters at conferences, APS meetings, AAS meetings, AAAS meetings, or what have you. Sometimes reporters go to meetings like that and meet scientists and then get to know them. Sometimes the scientist has done some work that is associated with the press release, and therefore they get known that way, or sometimes the scientist just has a public presence, blogging, Twitter, these days, whatever, writing popular articles.

0:57:35.1 SC: There's various ways that a journalist might get to know the name of a scientist. And then the journalist is going to very, very naturally have their favorite scientists to talk to. Scientists are not all equally adept at explaining science to a wider audience, or speaking in non-jargon terms, or even the slightly more subtle skill of providing a juicy quote, right? A quote that is both accurate but also makes things sound exciting rather than boring. Now, ideally, a journalist will try to spread the wealth, right? They will try to talk to various people, different people for different articles, different kinds of diversity along various axes, but life is short, you don't always get there. Sometimes you just want that juicy quote and you go for the same person over and over again.

0:58:23.4 SC: In a related question here, Scott Lewicki says, I'm gonna relate this even though it's not obviously related. "Frequently in your episodes, you will reference a previous Mindscape Podcast guest when talking to the current cast. There's often some great discussion that comes from this comparing, you're contrasting the views of more than one guest. Have you considered inviting back two or more previous guests and creating a panel discussion that you could facilitate? If so which guests would you bring together? And what would be the theme?" So I've considered things like that, but as you'll notice, I have informally instituted a policy where I do not repeat guests other than myself. [chuckle] That's a special dispensation for solo episodes, right? But other than that, I never have the same guest on twice. And a number of previous guests have asked to come on, in fact, people who I think would be great repeat guests. But this is something I thought about quite a bit, and I decided that the value added by... This goes back to the previous question. The value added just by forcing myself to spread out and not just have the usual suspects over and over again, is more than the value added that I would get by having a favorite set of guests and going back to them over and over.

0:59:38.8 SC: This is not to say that there are not very real benefits of having a favorite set of guests going to them over and over again. There's a sort of institutional memory that gets built up from previous discussions, you know ahead of time, the person is gonna have good things to say, etcetera, etcetera. But I do think that... A lot of people do that. A lot of podcasts have their favorite guests, they go back to, again and again. I do try to be different, to try to differentiate in some ways. And part of the spirit of Mindscape as I see it, is really about exploring the ideas. It's not about our favorite set of personalities to interact with. And again, this makes it a slightly quirky thing. So if you want me to spin it this way, you the audience for Mindscape are an elite group. [chuckle] You are willing to listen to a bunch of episodes that are driven, not primarily by the fact that you've already heard of the guest before. I suspect that for most people listening, many of the episodes, most of the episodes, I don't know, are with people you've never heard of before, but you would like to listen to this episode just because the topic is good, or even maybe the topic doesn't naturally appeal to you, but you have an assumption that there's some reason why I picked that person, there must be something worthwhile.

1:00:58.9 SC: And of course, I usually do have reasons why I pick the people. They don't always work out. Most of my guests, I think are very, very good, but there is certainly a spectrum of success, but you gotta do the experiment, right? You have to try different things. There's a comfort to going to the same restaurant every Wednesday and ordering the same thing, but then you might miss some things elsewhere on the menu, or at other restaurants. And given my own personal preferences, I tend to want to be more experimental, and given that plenty of other podcasts do it differently, this is one way to be different. So reluctantly, in some cases, I have stuck with the policy of not inviting guests back. Now, I make no promises that I will continue to stick to that policy, and part of it is also there's a rich get richer kind of thing. The kind of people you invite back or people who are like smooth talkers, who are good on podcasts, and those people get to talk in plenty of places, they don't really need Mindscape all the time. And sometimes I have people on the podcast who are less naturally good at talking, but still have interesting things to say, so I think that it's important to get to those people.

1:02:08.7 SC: No matter how wonderful a person is, and no matter how much you love listening to them, there was always a time when you had never heard of them before. There was always the first time when you heard of them. So I think that the possibility that the next episode is going to be some brilliant, magical person who you've never heard of before is a big thing that I try to keep alive, which would be less likely if I had the same people over and over again. Now, that's not exactly what you said. I mean, Scott, you're asking about having panel discussions with previous guests, things like that. I've thought about lots of things. I've thought about having a conference where you get people in, previous guests in the same place in the real world back when we would get together in the real world. I guess most of Mindscape's existence now has been in a pandemic, hasn't it? Maybe that's not exactly true, but it is getting there. And I thought of having different formats for different episodes with different numbers of guests and things like that. It's all... Number one, it's more work, [chuckle] because as I said, I have the current system down to more or less a machine that I can get it over with pretty quickly. There is a lot of behind the scenes time that it takes to schedule, to get people microphones, to get the transcripts done, all that stuff.

1:03:28.4 SC: And it becomes exponentially more complicated when there's more than one person at a time involved. So I haven't really come up with a great way to expand the format that would not be way more work for me with any obvious tangible benefit. If the benefit were huge, then maybe I would do it. But especially because many of these are on a remote, right? Many of these interviews and having multiple guests is even harder when you're doing things remotely. We don't see each other, as well it's harder to interrupt and to ask questions in real time. So I'm not leaning toward doing that at this time, but I do keep the possibility open, and I'm certainly open to suggestions about how to be creative with the format.

1:04:16.0 SC: Andrei Dinu says, "You explained in the past that the state of the universe could be described by a vector in a Hilbert space. The evolution of the universe is equivalent to the trajectory of this vector in Hilbert space, however, the state of a system with variable number of identical particles is described by a vector in Fock space, which is the direct sum of several Hilbert spaces. How is this last space called and why do you not refer to this space when you think about the universe as a whole?"

1:04:40.0 SC: There's a lot going on here. This is a technical level question, but I think it's interesting enough to the broader audience that I thought it was worth talking about. The point is that when you do quantum field theory, one of the reasons why quantum field theory is so cool is because even though when you quantize a single non-interacting field, what you get is a set of particles with a definite number of particles or some superposition of different numbers of particles, but when you let the field interact with itself or with others, that number of particles can change. So whenever you have a situation where particles are created or destroyed through interactions, field theory is a way to sort of summarize what's going on there. And one way of thinking about that is to construct what is called Fock space, which is to say there's a part of Hilbert space where there are no particles, the vacuum, empty space, then there is the one particle, Hilbert space. So you excite the field just enough to have exactly one particle, and that particle can be doing different things. It has a wave function, it has all the different infinite number of possible wave functions.

1:05:43.8 SC: Then there's another part of Hilbert space that has two particles, and all the way up, and then you add those all together because the wave function for the quantum field will be a superposition of zero particles, one particle, two particle, etcetera, and that sum is called Fock space, F-O-C-K, after Vladimir Fock, the Russian physicist and mathematician. So two things to say here, one is Fock space is still a Hilbert space. It's not a different kind of thing. It's a particular kind of Hilbert space that you construct by adding together these individual Hilbert subspaces, but it's still Hilbert space, so it's still perfectly okay to call it Hilbert space. Secondly, thinking of field theory in terms of particles is not completely comprehensive. It doesn't always work. It works when you can think safely about tiny perturbations in the field, right? Tiny fluctuations look like particles. So that generally refers to the perturbative regime of the field theory where you can just start with the vacuum and then perturb it by adding a particle or two, watching them interact. In more general circumstances, like when the Higgs field just smoothly evolves from zero to its expectation value in empty space, you cannot easily describe that in terms of particles at all. So the Fock space description is just not very helpful. So Fock space is a specific kind of Hilbert space that is only relevant in specific circumstances. It's not a more general concept.

1:07:12.1 SC: Jonathan Goodson says, "When you were a member of the World Science symposium... World Science Festival symposium on quantum mechanics, the moderator asked the panel, 'Will the scientific community reach a consensus within the next 100 years?' As I recall the other participants said, 'Yes,' but when it was your turn, you opined the consensus will be achieved within 50 years. What was your thinking in giving that response? And was it anything more than confidence in MWI and the ultimate competency of your peers?" I mean, part of it, just to be slightly flippant about it, is that 50 years is my go-to amount of time to make predictions, 'cause I will probably be dead. [chuckle] I'm not sure, or maybe I'll get lucky, but at the least it's a period of time when I cannot be held responsible whether I was right or wrong. So it's a good number to pick. But also yes, I am kind of optimistic that we are making progress on the foundations of quantum mechanics. Like I said, I particularly or I specifically think that many-worlds is going to be the right answer, but even if it's not, I still think we're making progress.

1:08:11.3 SC: I still think that we have a lot more IQ points worldwide trained on the problem of understanding the foundations of quantum mechanics than we had in previous decades. And I don't think it's an intractable problem either. So I think that there will be a consensus about it sooner rather than later.

1:08:28.8 SC: David Harrington asks a priority question, remember, to those of you who are do, priority questions are questions you're allowed to ask once in your life, and you can drop them into the AMAs on Patreon, and I promise I will answer them. I don't promise I will give you a satisfactory answer, [chuckle] but I will definitely answer that one way or the other, so choose your priority questions wisely, 'cause you're on your honor to only ask one ever in your life. And David says, "I have since reading Lee Smolin's book on Universes From Black Holes, been bugged by a simple question. Where does the energy come from? In Smolin's hypothesis, a black hole of only a few solar masses would create a full-fledged universe. Where does all that extra energy come from?" The short answer is that the energy of the universe is zero, at least in this model.

1:09:15.4 SC: This is just a fact of general relativity. That in a closed universe, in a universe whose spatial slices are something like a sphere or a torus or something like that, the total energy is zero, which you can roughly informally, but not precisely, think about as saying that there is a positive contribution from the energy of matter, from stuff, you've matter, radiation, dark energy, what have you, and a negative contribution from the energy of the gravitational field, the curvature of space-time. That's a rough informal thing. Really, what you should think of is, we're talking about cosmology and the whole universe, there's no reason at all that your intuitive notions of energy should even apply in this case. But at a formal mathematical level, there is a quantity that is conserved in general relativity, which looks energy-like and for a closed universe, it is exactly zero. Even more formally than that, the point is that you can, in general relativity, quantum gravity rather, you can imagine bubbling off a baby universe, as I've written about in my paper with Jennifer Chen and Alan Guth and Eddie Farhi and others wrote about years ago, in a way that costs exactly nothing because it has zero conserved quantities.

1:10:30.8 SC: So not only zero energy total in this universe, but zero angular momentum, zero electric charge, all of those things. So there's no obstacle to having quantum processes that create as many of these as you want. That's sort of the secret at the heart of the mechanism that Jennifer Chen and I proposed for making more and more entropy in the universe. If you can make more and more universes, each one of them adds a little bit to the entropy of the whole shebang, you can just increase entropy without bound.

1:10:58.8 SC: Matt Rapaport says, "It occurs to me that the act of observing or measuring of a particle requires hitting that particle with something like a photon, and then having the photon bounce back into a detector. I'm wondering if the act of hitting the particle during an observation might change the particles properties such as its momentum? If you wanted to measure the particles position with increasing accuracy, you would wanna use photons with smaller and smaller wavelengths, thus higher and higher energies, is this a reasonable way for a layperson such as myself, to understand the Heisenberg uncertainty principle?"

1:11:29.3 SC: Well, I kinda wanna say yes and no here. If you just want sort of an intuitive answer in a way that it kind of connects with your Newtonian feeling about the world, or your classical mechanics feeling about the world, yes, to measure the position of something small requires a small wavelength, requires a lot of energy, therefore, you're gonna have to kick the particle a little bit. But if you're a little bit more careful, if you're a little bit more trying to understand at a deeper level, that's not the Heisenberg uncertainty principle. The Heisenberg uncertainty principle has nothing to do with measurements or observations. I guess I shouldn't say that. It has implications for measurements and observations, but it's not about measurements and observations. The Heisenberg uncertainty principle is a feature of the states of particles, the states of any quantum system, whether or not they are observed. In quantum mechanics, the momentum is related to the position in a complicated way, because there is no such thing as either momentum, or position. There's a wave function. Momentum and position are observables associated with that wave function. And they are what we call complementary observables.

1:12:39.4 SC: And what that means is that if you have a wave, that is a wave function, if you try to compress that wave in space in position, okay? So this very, very carefully localized around some particular point in space, then the complementary feature of it, the momentum gets spread out all over the place. So if you have a sine wave for position, wave function, you will have a delta function for momentum. And vice versa, if you have a delta function for position, you have a sine wave for momentum, and if you have a bell curve, something that is spread out, but only a little bit, then you can have that for both at once. These are all statements about the wave function of the particle and how it has to be. It has nothing to do with measurements, again, it has implications for measurements, but it's not about measurements. So another way of thinking about it at a much simpler level is just think about a two-dimensional Hilbert space. So forget about position and momentum, think about spin, right? Think about the spin in the Z direction of some particle. It could be spin up or spin down. Now, the tricky thing is, you naturally think of spin up is pointing vertically up and spin down is pointing vertically down, but in Hilbert space, in this space of all possible quantum wave functions, these two possibilities are perpendicular.

1:13:56.8 SC: You are either spin up or spin down or you're some combination, but they are orthogonal to each other, so you make a plot of spin up horizontally and spin down vertically or something like that. And that's all with respect to the Z direction. And then if you ask about spin in the X direction or Y, let's just pick one, pick X. The X spin can be figured out in terms of the Z spin, but the way to figure it out is that the axes are rotated by 45 degrees. So the spin up with respect to X-axis is tilted at 45 degrees with respect to spin up and spin down in the Z-axis. So what this means is if a particle has a spin that is in a pure state of Z spin, so it's either pure spin up or pure spin down, it can't also be in a pure state of X spin. It's going to be an equal combination, an equal superposition of spin up and spin down in the X direction, just because the axes are tilted with respect to each other. It's a mathematical fact, not related to how we observe it or anything like that. That's the uncertainty principle.

1:15:10.9 SC: Samuel Cohn says, "I've heard you mention that the Hilbert space of the universe is large but finite-dimensional, how do you reconcile this with the commutation relation between the momentum and position operators? It's an elementary exercise that in a finite-dimensional space, if the commutator of two operators is a multiple of the identity, then the commutator is zero." Yeah, that's true. And just to be super-duper careful here, when I say things like the Hilbert space of the universe is finite-dimensional, that's a speculation. We don't know that for sure. We are saying that we have good reason to believe that the Hilbert space of our observable part of the universe is finite-dimensional. It's not an absolute statement that we know the answer to. But as you might guess, if you have a finite-dimensional Hilbert space, finite-dimensionality is really, really big, like 10 to the 10 to the 120 dimensions. That's pretty close to infinity for a lot of local purposes, so you would be very, very surprised if some persnickety mathematical fact that distinguish between finite and finite-dimensional Hilbert spaces really mattered.

1:16:19.0 SC: And indeed, in a finite-dimensional Hilbert space, you can construct analogs of position and momentum that are not exactly the same, but they have the same kind of commutator, the position and momentum do, and then you can take a limit as that number becomes really, really big, in the dimensionality of Hilbert space, they become more and more like position and momentum. So in fact, I did this with Ashmeet Singh, who was a student here at Caltech, we wrote a paper on doing exactly this, and I will read you the title of the paper, Modeling Position, and Momentum in Finite-Dimensional Hilbert Spaces via Generalized Pally Operators. Pretty good, huh? You asked a question that I actually wrote a paper about. So you can go to the archive and look for that paper, Modeling Position and Momentum in Finite-Dimensional Hilbert Spaces via Generalized Pally Operators. So it can be done. Obviously, I presume that you know a little physics here, if you're asking questions like that, so you should be able to read the paper and see what we have to say. It was just a... It came out in, what? 2020. Not too long ago. So there you go.

1:17:17.4 SC: Anonymous says, "Do you have any advice for casually talking about academic or intellectual interests and hobbies without coming across as bragging or trying to act superior? How would you describe the middle way between heavily editing yourself to make people comfortable on one extreme versus refusing a responsibility to read the room on a basic level on the other extreme?" So I just wanna make this question a bit more general because I think it's a question that's nothing to do with intellectual interests or hobbies or acting superior. It's just a general question about how do you talk about things you care about that the rest of the room may or may not, okay? If those things happen to be intellectual or whatever, that's great, and if they're not, that's also great. Maybe you like watching the rodeo, maybe you like knitting, and maybe no one else who you're talking to does, or maybe they do, and you don't know it, right? So I think that it's no different than if you like knitting versus if you like quantum mechanics, perfectly, honestly.

1:18:17.6 SC: The ways in which you might get a negative reaction differ in details. If you like knitting and someone is in... The whole room is full of macho people who would look down upon that, they might be condescending, whereas if it's full of a bunch of people who are anti-intellectual and you like quantum mechanics, then you might get defensiveness kind of reaction. But the general strategy is the same. Mainly, on the one hand, you should simultaneously be proud of your interests, you should not apologize for them, you should be able to express enthusiasm for things you're enthusiastic about, and at the same time, recognize that if other people aren't interested, then this just isn't the room to talk about that. You shouldn't force it on them, whether it's knitting or quantum mechanics. Some people are gonna be interested, some are not. Try to discover who those people are by maybe mentioning that you're kind of interested in this stuff, and if they're just not, then move on to something else. And if you're unable to talk to them about other things, if you're unable to find any overlap between what you're interested in, and what they're interested in, either then there's some issue with you, or more likely you're just in the wrong room, [chuckle] and you should go to a room where you can talk about stuff that you both agree are interesting.

1:19:33.8 SC: James Maddox says, "In the standard model, what is a mixing angle? They seem to determine strength of interactions and relate closely to symmetry and unification, but do they have a physical interpretation?" Yeah, they do have a physical interpretation. I mean, I don't wanna spend too much time because again, this is a technical or physics question, but basically think about quarks, okay? You have the positively charged quarks up, charm and top, and I might not get this right, which is positive and which is negative. Up, charm, top and then down, strange, and bottom, the negatively charged quarks. And roughly, they're in pairs, up and down are a pair, charm and strange are a pair, top and bottom are a pair. What does that mean? That means that the up quark when it interacts, when it either transforms, when it gives off a W boson, so it changes its identity, usually the up quark is gonna change into a down and the down is gonna change into an up, and vice versa. But not all the time. So the up quark is actually going to change into some linear combination of all the negatively charged quarks. So you have an up quark which is charged plus two-thirds, it gives off a W plus, right? A positively charged W boson, so it converts into a minus one-third charged quark. But it's not purely a down quark, it's a combination of up, sorry, of down strange and bottom. There you go.

1:20:58.2 SC: And that which combination it is, that's what the mixing angle is telling you, the precise amount by which you get these different combinations. Same thing is true with neutrinos and leptons and so forth. Roughly speaking, this is all just saying that there are different properties that quantum fields have, and the properties don't always march in lockstep. So in the neutrino world, for example, though the important fact is that there are mass states, there are... I should say the other way around. You may have heard that in the world of neutrinos, there are electron neutrinos, muon neutrinos and tau neutrinos. And what that means is, these numbers are conserved. So when a tau lepton decays, it's gonna have to give off a tau neutrino and then maybe like a muon and an antimuon you want, or something like that, Okay? No, that can't be right. [chuckle] Conserved charge, if a tau decays, it'll have to spit off a muon and then an antimuon neutrino, so muon number is conserved plus a tau neutrino, so tau number is conserved.

1:22:05.6 SC: Okay. But, what it turns out to be the case is that the states of definite mass are not purely electron neutrinos, muon neutrinos or tau neutrinos, they are mixed together. And figuring out what exactly that mixture is, is a very high priority thing that we're trying to do in the world of neutrino physics right now.

1:22:26.2 SC: Jake McNeil says, "Scott Aronson suggested that, during a lecture attended, the quantum computing might be a useful method of teaching core concepts of quantum mechanics. Do you think that might be a good approach to introducing quantum mechanics, especially for those with more of a computer science background rather than a math and physics background."

1:22:41.8 SC: You know, it could be... My brain is thinking these days about teaching physics students quantum mechanics, so that's what I know and care the most about. For computer science students, it might be different, there is a sense in which quantum computing is a generalization of classical computing, you replace bits with qubit and NOT gates, etcetera, with their quantum gate equivalents and so forth, and you have this whole new thing which is that states can be in super positions and then you have to read out the outcome with the measurement that collapses the wave function, but otherwise it is a generalization of the whole idea of bits and computing.

1:23:22.7 SC: So you could teach things that way. Sure. Absolutely. You're never gonna get to the hydrogen atom that way though, [chuckle] you're never gonna get to the simple harmonic oscillator or quantum tunnelling or a whole bunch of other interesting phenomena. So I think, honestly, my current thinking is to be hybrid about it, given that I am interested in how to teach physics majors, I take that they come into it knowing some classical mechanics. They know a little bit about positions and velocities or momenta of particles. That's how they're trained to think, a ball rolling around in a potential on an inclined plane, and the usual traditional way of doing quantum pedagogy is to take that classical system and quantize it to replace positions and momenta with wave function and go on from there. And I think that's fine. I think it's a good thing to do, but you instantly get into difficulties or at least sticky wickets, mathematically speaking, because the Hilbert space of a single particle is infinite dimensional, and infinity is harder than two...

1:24:27.3 SC: Qubit has a two-dimensional Hilbert space, which is a lot easier to deal with. So conceptually, qubits are a lot easier way to introduce quantum mechanics, the problem with them is they don't connect with anything you've heard of in classical mechanics, there's no equation of motion for a qubit, classically. Okay? So I think you can do both. I think you can say, "Here's a classical particle, let's quantize it. Oh, we get wave function. Oh, we notice that wave functions are vectors in a Hilbert space. Oh, we notice that there are much smaller Hilbert spaces than that, like two-dimensional Hilbert spaces," and then you use that two-dimensional qubit language to introduce a lot of the concepts of quantum mechanics, so just do both. That's what I would like to do, I would like to do both.

1:25:11.3 SC: Anonymous, these are all different anonymouses, this is not one anonymous asking many questions. Anonymous says, "The collection of homeostatic chemical processes we call life self-propagate in the direction of the arrow of time, because this is the direction where entropy increases. The intelligent computational systems based on these chemical processes we call our minds thus experience the arrow of time. As a whole, the entropy of the universe increases, but there exist regions where entropy decreases, could there be homeostatic chemical processes that propagate in the reverse direction in these regions, life in the reverse direction.?" So no, the answer is no. [chuckle]

1:25:48.8 SC: But it's a little bit tricky to explain why, and in fact, this might very well be something where I just don't understand it well enough to give you the simplest answer here, but let me explain to you why I'm quite confident that that is the right answer. The second of law thermodynamics applies when you have a closed system, and you say a closed system that starts in a state of low entropy will with enormously large probability evolve to states of higher entropy. There are ways to have systems spontaneously decrease in entropy, namely they're not closed systems, they're open system. So my favorite example, you put a bottle of champagne in the refrigerator and it will lower its temperature, and if you calculate the entropy afterward, it has a lower entropy, just 'cause it's lowered its temperature, that counts as lowering its entropy.

1:26:41.2 SC: But the point is that even though we say, and it is true, we correctly say that the arrow of time is due to the fact that entropy is increasing, that little glib motto slides over some important details, okay? [chuckle] So the details matter. And actually, this came through a little bit in the podcast with David Wallace, where we were talking about the arrow of time that, sure, entropy is increasing, but there's more to it than that, entropy is increasing in a particular way. So think of it this way... So roughly what I wanna say, just to get to the answer of your question is, if I put something in a refrigerator, its entropy will go down because it's a closed system, but there's no... It's an open systems, sorry.

1:27:22.6 SC: There is no sense in which the arrow of time is reversed inside that bottle of champagne, and the way that you can see this is, think about a very typical thing that we use to illustrate the increase of entropy. If you have a cup of warm water and you put an ice cube minute, the ice cube melts and you get a cup of cool water and entropy is increased along the way, okay? But if you take that cool water and now you put it into a refrigerator, it's not gonna... It will lower in entropy, if its coolness is not quite as cool as the refrigerator, it will lose, it will radiate photons and heat out to its environment, its entropy will go down. But it will not spontaneously form into an ice cube plus a glass of warm water just from sitting in the refrigerator. The whole thing is just gonna cool down, okay? So there are differences in the details of the way in which entropy increases or decreases in a closed system naturally increasing entropy versus an open system leaking entropy out into the world around it. And there's details there upon details that I'm not gonna get into, but the short answer is, you don't expect a reversed arrow of time in an open system that is going downward in entropy.

1:28:36.1 SC: Jim Watson says, "Regarding cosmic red shift you to expanding space, time, where does the energy loss from the photon go as it is red shifted." Two answers to this, depending on what level that you care about, one answer is energy is not conserved. In an expanding universe, the total energy of stuff, of matter and radiation, etcetera, is not a constant number because spacetime is changing underneath it. Okay? I wrote a whole blog post about this. If you go and Google 'energy is not conserved,' you'll probably get my blog post about this. The longer answer, which I have to give... Usually I stop there, the longer answer 'cause I have to give it now, 'cause I've already mentioned that in general relativity, there is a conserved energy that includes the energy of the gravitational field. Okay?

1:29:18.4 SC: So the energy that is not conserved is just the energy of the stuff inside the spacetime. If you try to attach an energy to spacetime itself, you can do that, it's tricky, there's details, there's mathematical subtleties, but you can do it and that number is conserved. So in that way of thinking about energy, 'cause there's no single way of doing it, there are different ways of doing it. In that way what you would say is that there is a transfer of energy between spacetime and the photons. If it's photons, they lose energy, which is absorbed by spacetime, if it's dark energy, dark energy increases its total amount of energy in a certain region of space as the universe increases. So energy can either go up or down in stuff, and in either case, spacetime responds appropriately.

1:30:09.5 SC: Rue Phillips says, "David Chalmers refers to you in his new book, Reality+, he believes we are in a pure simulation. His credence comes from statistical analysis. If it is possible for someone in our universe to create a pure simulation, then it will be much more likely that are sims, because it is much easier to create billions of Sim worlds, than the universe to create billions of physical worlds with life. What are your credences on these concepts, and what if anything is Chalmers neglecting in his argument for us probably being sims?" I'm not gonna give a full account of this because I think these are subtle issues, but what I really think is that people tend to misuse anthropic reasoning in this case, and this is something...

1:30:53.2 SC: I don't wanna be too mealy-mouthed about it, but I'm not completely sure that my opinion is the right one, but it is my tentative way of thinking right now. As I said before, the simulation argument, there's a step... If you take the simulation argument to just say, maybe we live in a simulation then that's fine. That's completely true, maybe we do. But if you take it to say we probably live in a simulation, well, then you're assuming some measure on the space of who we could be, and people tend to use some kind of principle of mediocrity or, typicality or whatever you wanna call it. We are randomly selected from the set of all possible people, intelligent beings in the universe, and I think that's just wrong. I don't think you should assume that we are randomly selected from the set of all people in the universe, there's many ways in which I am not randomly selected from the set of all intelligent observers even here on Earth, much less in the whole universe. So I think that step just doesn't work, what I would rather do, as I said before, is to ask the question, "What would the universe look like if it were simulation? And I don't think it would look much like our actual universe does.

1:32:00.4 SC: To be a little bit more clear about that typicality point, here's the way that I like to put it. I'm borrowing language from other people, and I forget who it is, so I can't give credit. Sorry about that. But it seems humble when you say, "I think that I'm just a typical observer in the universe," that's why it's literally sometimes called the Principle of mediocrity. But you don't know what a typical person in the universe looks like. You don't know about the space of all possible observers in simulations and elsewhere and space or whatever, you have no idea, right? So really, when you're assuming that you are just a typical observer, you're actually assuming the typical observers are like you, and that's not humble at all, [chuckle] that's sort of maximally arrogant. You're assuming that you can infer some facts about all of the observers in the universe, just on the basis of your local parochial experience of the world. So I think that's wildly unwarranted by anything that we know about reason or logic or experience or anything like that. I do think there are ways to still make anthropic-like arguments, I think that it's okay to say that models of cosmology that make it more likely that observers like us would exist...

1:33:14.2 SC: Observers exactly like us. So forget about typically, observers exactly like you, okay? Models of cosmology that make it more probable that a person exactly like you would come into being should be preferred in a Bayesian sense over models that have low probability of you coming in to being. That's the kind of thing that I would think is okay to say without making any assumptions about your typicality in the cosmos.

1:33:39.7 SC: Joe asks, "Have you ever used Linux on a desktop, laptop or server? If so, what did you think of it?" So yeah, I did when I was at the University of Chicago for several years, I had a Linux desktop machine. It was fine, I'm not... My attitude towards these things, operating systems and so forth is, there's no right or wrong. Some are better than others for different purposes, but different users and different sets of needs are going to be better served by different operating systems. So if you're really into it... [chuckle] If you're really into operating your operating system, getting into the guts of it and changing things around to please your whims, then Linux is great, you can tinker with it. If you just wanted to work and forget about it, if your intellectual energies are focused elsewhere, then Linux is not the operating system for you. So I'm very happy with the Mac these days, I don't love being beholden to the Mac ecosystem overall, but the things that they do are good enough for me that it works fine. And there is a cost in switching back, so the iPad, iPhone, MacBook Pro combined system works quite well for my own needs, and so I have no motivation to contemplate switching.

1:35:00.2 SC: Jeff B says, "As I listen to your interviews with guests, I'm always impressed by your ability to come up with questions that cut to the heart of a topic, do you believe this is something that you're naturally talented at, or was it a skill that took practice?" Well, thank you, Jeff, for the nice compliment, like I said, I am not above including questions here that involve the compliments, that to begin with.

1:35:18.8 SC: So I'm not sure though, to be super duper honest here, I'm not sure that I have a special ability to come up with questions to cut to the heart of a topic. What I do think is that there's a simple feature of Mindscape, which is that it's just me, [chuckle] I am the one choosing the guests, booking them, interviewing them, whatever, and my motivation for doing it is not primarily greed or fame, it's 'cause I'm interested in what these people have to say, that is literally my primary motivation. I started the podcast 'cause I wanted to talk to these people and hear what they had to say, learn from them. So I think that gives me a leg up. I'm not a professional interviewer who's handed a guest and some talking points and asked to talk about them, if I'm inviting them on the podcast, there's something that they know that I would like to know. [chuckle] So I'm just being sincere in my questioning because I'm actually trying to get at what it is they have to offer. There's one aspect that may or may not be relevant here, which is that you do get trained as a scientist and not just a scientist, but as an academic more broadly, you get trained to understand things in such a way that you could do research on them, right?

1:36:32.1 SC: You know, it's one thing to be handed a book or a paper and say read it, it's another thing to be handed a book or a paper and say, read it, and there will be a test on it, okay? So you're gonna be a little bit more careful reading it, if there's gonna be a test. It's a whole another thing to be handed a book or paper and say read it, and then do your own research and write a follow-up paper or a book, that's just a whole other level of understanding, and that's just what you're trained to do as a professional academic. So, I do try to understand things in such a way that I could afterward...

1:37:03.7 SC: It's certainly not true for all the podcasts I do, that I could then go off and do research in these areas. But it's the beginning of a start to understanding things well enough to be able to do that. So I'm not gonna be satisfied with words that sound like I understand it, I really need to understand it well enough to think that I could sort of use the ideas myself at a research level. Even, it's not true, as I just said, that I could actually start doing research, but it's the beginning of that process.

1:37:35.5 SC: Patrick Hall says, "You've spoken extensively on the importance of increasing interdisciplinary projects between Philosophy and theoretical physics, what branch of philosophy do you think can benefit the most from collaborating with theoretical physics? Do you think the problems of metaphysics can be solved with theoretical physics?"

1:37:51.0 SC: I think that this is... Like it's a kind of a hodgepodge, I guess. I don't have a systematic theory of what kinds of philosophy can benefit from physics or vice versa, but there's a general kind of obvious set of ideas, right? I do think that philosophy is continuous with physics, they're not really separate things, they're both attempts to understand the world, and probably you can throw in Mathematics and a bunch of other things that are in some sense continuous. It's we human beings, especially university administrators who end up drawing these bright lines between these different fields, but if there's a philosopher thinking about what is the correct formulation of quantum mechanics, and there's a physicist thinking about what is the correct formulation of quantum mechanics? They're doing the same thing.

1:38:36.3 SC: They're asking the same question. Okay. Whatever department they might be in. So the kinds of problems that... Forget it, I won't necessarily accurately answer your question, but the kinds of problems that I think are most interesting at this intersection are questions where our physics knowledge needs clarification. Okay, so it's not just we need more data, but we need more clarity of thought, and there's plenty of ideas like that in cosmology, in quantum mechanics, in statistical mechanics, in entropy and so forth, that's sort of... I'm answering the inverse question, what can physics ask up for philosophy? What philosophy can get from physics is more like... Well, two things, one is they can be inspired by discoveries in physics, right? It's too easy in certain areas of philosophy to sort of lazily think that features of the world you're familiar with are necessary. Right.

1:39:42.8 SC: There's an argument about whether Immanuel Kant thought that it was necessary that space had three dimensions, [chuckle] he wasn't always clear, so it's not obvious what he thought. But it's not necessary in any logical or mathematical or physical sense that space had to have three dimensions, it's a feature of our world. So even the existence of space itself is something where I think a lot of philosophers just take for granted, and you will hear them say that we couldn't have, I don't know, interactions or structure or memories without spatial locality, which I think is obviously not true, 'cause I don't think spatial locality is fundamental, so that's an area where you can really learn something from listening to the physicists, I think. And finally, you can just be inspired in the sense of being given new questions to ask.

1:40:30.5 SC: Philosophers invent things like the Sleeping Beauty problem or other thought experiment kinds of things, and physicists come up with real questions about Boltzmann brains and the multi-verse and you might think those are very speculative, but they were not invented to be cool philosophy puzzles, they were invented because they might actually apply to the world. And so those new puzzles that come in are directly germane to metaphysical questions. You read David Lewis, and a lot of the stuff that he did is pretty directly resonant with modern physics, even though he wasn't pretending to actually do more physics himself.

1:41:08.6 SC: Rob F says, "As a lay person, it seems strange for me that the square root of minus one is of such fundamental importance to quantum physics and by extension to nature, can you help me understand why this imaginary number is of such importance versus any other type of number?" I do think that there's kind of two levels of answering this question, it's sort of the math level and the physics level. The math level is, why were you ever motivated to invent imaginary numbers in the first place? And I think that's a very natural answer coming just from the natural progression of mathematics toward greater generality and abstraction, like if you have an equation like two plus three equals five, that's good. You can understand that, no issues, and then you try to generalize it. So you say, well, what if X plus three equals five, I'm not gonna tell you at X is, but then you can solve and you can figure out, you can solve that equation X must equal two okay? And you're still very happy... This is... We're talking about 3000 years ago. You could still have had that conversation.

1:42:09.3 SC: But then someone says, "Okay, wise guy, what about if X plus three equals 1, what are you gonna do then?" And you can say, "Well, you know what are we gonna do?" We're gonna invent negative numbers, and I know that now we just take those for granted, but back in the day, that was a big deal. You would say, "If X plus three... " Sorry. Yeah, X plus one equals five, then X has to equal... If you say X plus three equals one, then X has to equal minus two, and you can sort of intuit your way into that, like there are... You could have money or you could have debts, so debts are kind of like negative money, and imaginary numbers are invented the same way. You say, X squared equals four, cool, so X could be plus two or minus two. But what if X squared equals minus four?

1:42:57.2 SC: Well, you could just say, there's no solutions, that's okay, but maybe you like the idea that every time you have an equation with X squared in it, any time you have a quadratic equation, there are two solutions, maybe you like that idea. That's tricky, 'cause if X squared equals zero, the only solution is zero, but then you talk yourself into thinking that you have zero two different times. And more generally, if you have X squared equals minus four, you could say that X equals plus or minus two times the square root of minus one, two times high. So you invent imaginary numbers that way. And that might be just not very useful mathematical abstraction if it weren't so useful, so that's the second level of the answer to your question. Why does this mathematical construction find so many uses in physics? That's a more tricky one because you never need imaginary numbers, you never absolutely, absolutely need imaginary numbers. You could always just replace any discussion of imaginary numbers with separate discussions of their real parts and their imaginary parts, you're allowed to do that, it's just much less convenient. So the question becomes, why is it convenient to talk in the language of imaginary numbers? So I'm gonna try to give you an answer. [chuckle]

1:44:13.7 SC: We'll see whether it actually works or not, so here's my attempted answer. Think of the double-slit experiment. Okay? Think of an electron wave function, it's a wave that's passing through two slits, and on the other side, it interferes. So what are the features physically, that you want to have happen? And forget about observations and decoherence and all that stuff, we're just thinking of the simple wave goes through two slits and get an interference pattern on the other side. So one thing is, it's clearly got a wave, right? It can't be particles if you're getting an interference pattern on the other side. There needs to be a contribution to what you're seeing on the other side, which is partly a positive part and partly a negative part, so they can... Some places cancel out, that's what it means to get an interference pattern, so that's why waves are the natural place to look, the wave could be up or down, it could be positive or negative. So you might think, "Okay, I'm gonna invent something called the wave function is gonna be real valued, but it could be positive or negative."

1:45:14.2 SC: But then you say, "Well, if I observe the particle somewhere along the way. Okay? Then I need a probability of observing it," and for various reasons, you want that probability to look like the wave function squared. Okay? If the wave function is a real number and the probability of observing it is the wave functions squared, and that wave goes up and down, so it's positive then zero and negative, and zero and positive, etcetera. That means that the probability of finding the particle at all seems to be oscillating between zero and one, that's not what you want, you want the probability of the particle being somewhere just to be one all the time. So this is a job for imaginary numbers or for complex numbers, more generally. If you say that the wave function squared equals one, I mean, if it's really the integral of the wave function squared, but hopefully you know what I mean. If the wave function squared overall has to equal one, but you also wanted to go up and down and be able to interfere, that's what complex numbers can do because it's not really going between positive and negative, it's circling around with constant magnitude in the complex plane. Okay? That's an attempt, I don't know if that attempt worked. That's an attempt to explain how negative numbers become... Or imaginary numbers become very, very convenient in real world physics situations.

1:46:37.3 SC: Anonymous says, "What are your thoughts on the current graduate student employment crisis? As an undergraduate student, I was blissfully unaware of the extreme number of steps one has to take and road blocks that are in the way when one wants to work as a PhD scientist, grad school, postdoc, little or no control over the final location. Does the academy have a responsibility to make prospective students aware of what they're likely walking into, even though it doesn't benefit the academy? Are there any creative solutions you thought of besides moving the bottleneck from getting a job to getting into grad school?" I do think that we absolutely have a responsibility to make prospective students aware, and I try very hard to do it. Every student who is either a prospective student or one who has arrived and wants to work with me, we have the talk, [chuckle] and the talk involves saying, "The odds are against you," you get a PhD from the best place in the world, and the odds of getting... Becoming a tenured professor is still small.

1:47:33.8 SC: Well, maybe one in four. I don't know, that's the number I heard once in my life, and I think that's in the right ballpark. It's not 1%, but it's not 90% either, it's somewhere in between. I think we do need to let people know and then let people choose whether or not they want to do it anyway, I don't think the solution is to just let fewer people get PhDs. For lots of reasons. One thing is, there's more reasons to get a PhD than just to become a tenured professor somewhere. Getting a PhD is a useful thing. It's education, it's a degree, you can become a smarter, better thinker by getting a PhD. And so it's not like you've completely wasted your time if you get a PhD and then don't end up being a professor. But I do think you should make that decision yourself, right?

1:48:23.4 SC: So if we... Think about it this way, if the graduate schools just stop taking as many students, that means the graduate schools are deciding for all those people they're rejecting that they shouldn't get a PhD, because maybe they won't get a job. I don't think that should be the graduate school's decision, I think that should be the student's decision, they should make the decision with all the information they can possibly have, but it should be their decision to make. The overall problem, honestly, is just not solvable, if you define the overall problem as. There are more people who would like to be tenured professors than there are tenured professorships. That's just a feature of the arrangement of society and the way that we distribute our wealth and things like that. Okay? That's not going away any time soon. And to sort of conflate that fact with some statement about graduate school admissions is a mistake. There's a lot more people who wanna be professional basketball players, than there are room for professional basketball players. I think that's not going away any time soon.

1:49:30.9 SC: There is one tweak I would make to the system that I think is pretty obvious, which is not, we should have fewer grad students, but that we should have fewer postdocs. As you say, in fields like theoretical physics, anyway, you spend five years getting a PhD and then you get a post-doc, which last for three years, just doing research, trying to buff your resume, your list of publications so you can apply for faculty jobs. And these days regularly people get two or three or even more postdocs. And that's much less defensible, I think as a system, a PhD is an education.

1:50:09.6 SC: You're in school, you're getting a degree, postdocs are just sort of training programs for researchers. And if you spend five years getting a PhD and then six or seven or eight years as a postdoc, it's hard to then switch into a completely different field. So I actually think this was... I give credit to Kim Boddy, who was a graduate student of mine when she first applied for postdocs, she said, "I wish they were a fewer postdocs out there," because of exactly this reasoning. And I had never thought of it before, and she's exactly right. She actually made it. She's a professor now at the University of Texas. So congratulations to Kim. But I get the logic, professors love postdocs because they're trained, they can do research, they help make professors really, really productive. I'm much less convinced that it's good for the postdocs themselves, it's a small tweak. That's what I would do. I'd provide more funding.

1:51:05.8 SC: In a world of grant funding and institutional funding, I would put more of it to supporting grad students, less of it to supporting postdocs, even though I like having postdocs around. They're pretty awesome.

1:51:18.7 SC: Anonymous says, priority question. "Would it be possible to calculate the minimum size the universe would have, assuming it's infinite to have all possible interactions take place, this would be assuming all possible outcomes are realized in many-worlds." So this is always the danger with priority questions, I have no idea how to answer this question. Sorry about that. I don't even know what it means, to have all possible interactions, I literally don't know what that means. Is that all possible interactions between two particles at a time or all possible configurations of all particles. And I have no idea how that is associated with the size of the universe at all. And further more, I don't know how many the interactions there are or anything like that Sorry about that, I just had zero idea of how to answer this question. I don't think there's any... To try to be a little bit more constructive. I don't think there's any relationship between the number of possible interactions and the minimum size of the universe at all. But I don't know, I might be wrong because that seems to depend on features of the laws of physics that I don't know the answer to.

1:52:22.1 SC: Sid Hab says, "On Quora recently someone as why gravity has been so difficult for science to reconcile with quantum theory. Victor Toth the physicist who often responds to questions such as this referred to semi-classical gravity. While he called semi-classical gravity an ugly kludge, he also noted that in all regimes that's accessible to us, semi-classical gravity provides answers that agree with experiment. What exactly is semi-classical gravity? Is it a step forward towards solving the problem of quantum gravity?" Yeah.

1:52:48.8 SC: Semi-classical gravity is just gravity when you quantized it, but don't push it too far. Okay? So when I talk about the core theory, the core theory includes both the standard model of particle physics and quantum gravity, but that quantum gravity is restricted to weak field gravitation. You can just take the ordinary classical dynamics of general relativity and turn the crank on quantizing it. Where that breaks down is where you go to higher order interactions with gravitons running around loops and so forth, and even more importantly, in black holes or cosmology, singularities, the Big Bang, stuff like that. But, okay, don't include that stuff. If you wanna know why the Earth goes around the sun or why apples fall from trees, you can quantize gravity in this weak field, not very dramatic regime perfectly well, and that's same classical gravity. The problem is, no, it is not a step forward towards solving the problems, 'cause all the problems are in the regimes where semi-classical gravity doesn't really apply.

1:53:47.5 SC: Cooper says, "I've heard David Chalmers and other proponents of the hard problem of consciousness completely dismiss emergence as a viable answer to consciousness. In fact, this dismissal appears to be one of their primary arguments against physicalism. However, it's not as if we have finished the work to comprehensively describe every element in the emerging ladder between quantum field theory and say, a chair. And yet I don't hear philosophers fretting about what it's like to be a chair. Do you think there is hypocrisy here in the philosopher's attitude towards emergence?" No, I don't think it's hypocritical. I don't agree with it either, so it seems strange for me to defend the formulation of the hard problem of consciousness, but it is an argument that makes sense. It maybe not be right, but it's not cheating in any way. The argument is supposed to be the whole point of drawing the distinction between the hard problem of consciousness and the easy problems, is that the hard problem is supposed to be a different kind of problem than describing a chair or something like that.

1:54:44.2 SC: Okay, so of course, you're correct that we've not described all the emergent levels in between quantum field theory and chairs, but it seems that all of those levels are sort of connected in pretty straightforward physical ways, atoms are made of particles, molecules made of atoms, all the way up to chairs made of whatever. Whereas the claim is that consciousness is not like that, and the reason why it's not like that is because it has this ineffable first-person experience what it is like to be something kind of thing. There is nothing that is like to be a chair, that's a different kind of problem. So the argument is supposed to be that you can have all the emergence want, you will never reach consciousness because it's a different place to be than just being a chair. Now again, I don't believe that argument, but I don't think it's necessarily anthropocentric or special or anything like that, it's just... I just don't... I think it's a failure of imagination more than it is a being too hypocritical or anything like that.

1:55:51.1 SC: Jimmy Summer says, "Does intuition tell you that the universe began with the Big Bang or some eternal cyclic model? It seems in the former, the universe has to come from nothing and the latter, the universe doesn't have to come at all, but only because it was always here. Should one seem more likely than the other, do our intuitions even mean anything when it comes to these kinds of questions?"

1:56:08.6 SC: I don't think our intuitions should mean very much honestly, when we are talking about the beginning of the universe, what does my intuition know about anything at all? Having said that, there's two little footnotes to that statement about intuition. One is that, of course, our intuitions can get trained, right? We get an intuition just from biology and from our experience of the world, but as we learn more about theories of the universe that are beyond our everyday experience, our intuition can grow to encompass the way that those theories work. The other thing is that we need, as we talked about before in the discussion of Bayesianism, you need some kind of prior on something. So if you don't know very much about The Theory of Everything or quantum gravity, but you do know that the either the universe had a beginning or it didn't, Bayesian reasoning says, you gotta put a prior on, the universe had a beginning or the universe didn't. I think that the right thing to do in those cases where there's no empirical difference to us today, and there's very, very little theoretical guidance is to be pretty open-minded. So take whatever priors you want, but I think it makes sense to have priors that are not too wildly different between the universe lasted forever and the universe had a beginning. Both are very much on the table.

1:57:27.7 SC: Daniel O'Neill says, "As a physicalist, how do you explain suicide having lost to close family members... Member to suicide, I find it hard not to think of it in dualistic, non-deterministic terms as an incorporeal mind choosing to destroy its own body." I'm sorry to hear about your family member. It's always a terrible tragedy when that happens. I shouldn't say that, I should say, it is often a terrible tragedy when it happens. I am someone who believes that people should be allowed to end their own lives under precisely the right circumstances. When they are of sound mine, they discuss things with their doctors, and so forth. So there's different ways in which that kind of thing can play out. But there's absolutely no question, a lot of circumstances under which people are in depression or something like that, whether it's external circumstances or their neurological signals failing them that causes them to commit suicide when maybe a day later, they wouldn't have. And that's a completely different situation, I've also known people to whom that has happened.

1:58:38.1 SC: I don't really think that there's any issue here about physicalism versus dualism, to be honest. If you're a dualist, like you say, you can imagine the mind choosing to destroy the body, if you're a physicalist, the body is deciding to destroy itself. So the question is, are you the kind of physicalist who thinks that you can come up with an explanation of free will and making decisions and things like that. So I am that kind of physicalist, so when people do things to themselves, whether it's suicide or something much less dramatic, I don't necessarily need to interpret it in terms of any dualistic terms.

1:59:12.5 SC: Related question, Casey Mahone. "What are your thoughts on euthanasia?" So I just gave them. I think that it should be allowed, but I think it should be controlled. You really wanna make sure that people are doing this in the clear light of day as it were, not because of some temporary chemical imbalance or temporary condition that they're in or whatever. But if you're facing terrible diseases that are not gonna go away, I think that there's absolutely a place for that in a well-formulated society.

1:59:43.0 SC: Anonymous says, "We have a lot of information from history and a lot of smart people on the planet, why is it that we can't get these smart folks to figure out a solution to what's going on in the Ukraine. Smart folks found a decent vaccine for COVID-19, why can't we just put an end to war?" Well, the glib answer is finding vaccines is way easier than finding end to war. Human level questions are always gonna be much more complicated. But also I think the question is a little bit misplaced in the sense that there are people who wanted the war. There are people who started the war, it's not like everyone agrees, we should find a solution to it. The reason why we have wars is because people have incompatible desires, right? Some countries wanna control other countries or just want... Think that they've insulted or whatever it is. Whatever the economic, social, political, religious motivations are, they're incompatible with each other. So it's nothing different than people... Well, it's a little bit different, but it's related to the fact that people get in fights, people get in arguments. People do this all the time, it's part of the human condition. And so I don't even know if there is such a thing as an end to war, as long as we are human beings. What we can try to do is minimize war and make it not be that bad. Right? I do think that when countries get to be prosperous and democratic, trading with each other, they are less likely to go to war.

2:01:08.6 SC: There's no absolutes here, there's no hard, bright lines between when countries will or will not go to war. But look, The United States and Canada are not gonna invade each other any time soon. They might annoy each other, but they're not gonna send troops to control each other. And France and Germany are not gonna do that. France and Germany is a much bigger... Much better example here. Nobody thinks that France and Germany have any non-trivial probability of invading each other any time soon, but they've invaded each other a lot over the last few centuries. This is real progress that those are two countries are not gonna do that. So progress is possible. Okay? We're very, very far away from some Utopian situation like that, but we can work to construct an international order where invading other countries just isn't done that often. It won't be 100% but we can work to it. It has nothing to do with being smart. It's not like there's a puzzle that we're solving like finding a virus or something like that. It has much more to do with motivation, values, like I said, and those are trickier things to deal with.

2:02:14.8 SC: Russell Wolf says, "Last month, you answered a question from Pablo's Papa-Joju about having multiple conceptually different models of physics, and mentioned the possibility that the ultimate theory might include multiple models that each have different domains of applicability. As you were describing that, I started to wonder if quantum mechanics and relativity are an example of this scenario because they use very different language, but agree in the classical limit. But then you finished by saying, we're nowhere near this becoming a realistic question to worry about. So what's the difference between the hypothetical you were describing and the situation in physics Today?" Well, there is an overlap between the regimes described by gravity and the regimes described by quantum mechanics. So you said relativity. Relativity and quantum mechanics are 100% compatible. I think you mean gravity, which is classically described by general relativity, but we don't have a good full theory of quantum gravity yet. As we said, we have a semi-classical theory, but we don't have the full theory yet, but it's not hard to look at regimes where quantum mechanics is important, and gravity is important. My favorite regime is the sun.

2:03:19.5 SC: The sun causes gravity, it also causes heat and light, both of these are very important to our lives here on Earth, that heat and light are generated through quantum mechanical processes. You cannot consistently describe what the sun does by not including both quantum mechanics and gravity. Now you sort of use different languages when you do that, but it's the same physical situation. So I was imagining a situation where different physical situations are described by different models, and those sets of physical situations don't overlap, but for gravity and quantum mechanics, they definitely do overlap.

2:03:54.7 SC: Liam McCarty says, "My understanding is that an interpretation of a theory is so called because it doesn't imply any difference in experimental results compared to other interpretations. If so, I'm curious how you pick one over the other. Is it based on Occam's razor, or do you interpret such an argument to advocate for the many-worlds of quantum mechanics?" So I guess the short answer here is you're probably implicitly going on the idea that we are deciding between different interpretations of quantum mechanics, but we're not. That is just not the modern discussion that we have in the foundations of quantum mechanics. I will often talk about the many-worlds interpretation because that is the label that was given to it back in the day, but it's a theory. It's not an interpretation of anything. It's a physical theory. It has a set of things, in this case, the wave function of the Universe. It has a set of rules for what happens to those things. In this case, it obeys the Schrödinger equation. Okay?

2:04:51.3 SC: It's an ordinary physical theory. The Copenhagen interpretation is in some sense an attempt to interpret something, but it's unclear what it's interpreting or how it's doing it, but many-worlds compared to like super-determinism theories or pilot-wave theories or whatever, these are just separate distinct physical theories the word interpretation there is just old-fashioned and doesn't really apply anymore. If you did have a situation where you had a single agreed upon physical theory, but there were different ways of interpreting it, then it's just up to you. Go nuts, right? If you think that Newtonian mechanics is equivalent to Lagrangian mechanics or Hamiltonian mechanics, the same exact physical happenings described using different words, I don't think there's any right or wrong there at all, you just use whatever is most convenient for the situation you're in.

2:05:41.9 SC: Kevin O'Toole says, "Whenever I hear the word decoherence in quantum physics, I can't help but think it's named backwards. If an electron starts in a state totally uncorrelated with anything else, then evolves into a state where it's highly correlated with many other particles, the latter seems distinctly more coherent. A measured particle seems more coherent than an un-measured particle. In what sense is it intuitive to think of decoherence as a process of becoming less coherent?" Yes, that's perfectly fair. I get exactly where you're coming from. The reason for the lingo is that the issue of decoherence first drew notice in the context of, you start with two particles that are entangled and then you measure one of them or one of those two particles becomes decoherent. It becomes entangled with the rest of the world. So imagine you're trying to build a quantum computer, okay? So you have qubits and you want them to remain entangled and do their thing, so you put them through gates and they evolve according to the gates and the Schrödinger equation, while remaining entangled in the appropriate way. It would be a shame if some photons came along and bumped into one of your qubits, and then that qubit became entangled with those photons, but it becomes un-entangled with the other qubits in your quantum computer.

2:07:00.7 SC: That's why it's called decoherence, because within the set of entangled things, measuring one of them or entangling one of them with the environment, decoheres it or disentangles them with everything else. It's not the best word. I agree on that, but sometimes we're stuck with the words that history gives us.

2:07:20.7 SC: P. Walder says, "Within discussions around the concept of panpsychism, the nature of matter is frequently queried. In particular, Philip Goff suggests that physics on a fundamental level only describes what matter does and not what matter is. Can you give an explanation of what matter is?" I'll be honest, I don't think this distinction makes any sense between what matter does and what matter is. What matter is is matter. The stuff of the universe. I don't even like to use the word matter, because that has some pre-existing baggage that it comes along with. I think there's the physical universe, okay, and we're looking for ways to best describe it. I've argued that our best current description is as a vector in Hilbert space, but other people will disagree, that's fine. But it is whatever it is. I'm not even sure it would make sense to ask what matter is or what the universe is. It's the universe. It's sui generis. It is by definition a unique thing, okay? Even if it's many-worlds, and what we mean by the universe in this sense is all the worlds together. There's nothing like it.

2:08:19.9 SC: How in the world would you explain what matter is in terms of something else? Right? I just don't know what that even means. I do know what matter does or I know certain things that it does, that's all of physics, all of science is what matter does. So that makes perfect sense to me. I think that the desire to explain that matter is something is just a leftover from a pre-scientific way of thinking about things.

2:08:46.7 SC: Mishi Stern says, "I recently heard your interview with Daniel Dennett. You discussed the Manifest and Scientific Image. My question is, as the years go by, do the things in the realm of the Scientific Image move to the realm of the Manifest Image? What once was considered essential becomes a useful superficial description from molecules to atoms to neutron, protons, electrons to quarks to leptons, etcetera." So I think yes and no, it's gonna be one of those yes and no answer questions here. The Manifest Image is never quarks and leptons, that might be the best image we have.

2:09:17.7 SC: But the Manifest Image is supposed to be manifest, that is to say it's supposed to be right in front of our eyeballs at all times. Okay? The Manifest image is supposed to be the world that we instantly see when we look around, tables and chairs and computers and microphones and things like that. Your scientific image gets better and better, you realize that the... Things are made of atoms and quantum fields and so forth, that doesn't change the Manifest Image at all, and in fact, I honestly think that the whole idea of the Manifest Image is under-appreciated. I think that sometimes we skip over it when we think about interpreting things philosophically or scientifically, we go from...

2:09:58.5 SC: We try to say that this is the world at the fundamental level, and we kind of imagine that we apprehend that world directly, but we don't. Everything that we see is moderated through the Scientific Image, even sorry... The Manifest Image rather. Even if you look at a picture of... A crystallite graphic picture of some atoms in a solid, you're looking at a picture, you're looking at a photograph, you're not looking directly at the atoms, even if you're staring through a microscope, you're staring at some dots on a screen. So I think the Manifest Image actually plays an important role in how we interpret the world, we're constantly comparing the parts and features of our best scientific practice to the Manifest Image. So I don't think it really changes over time, it might change a little bit if you learn this and that, and it's easy to flip a the switch and go, "Oh, the Earth goes around the sun, not the other way around." That's fine, but the fact that there's something called the Earth and something called the sun, those are both part of the manifest image, and they're not going anywhere.

2:11:01.6 SC: Napoleon's Corporal says, "I recently read somewhere that Bell's theorem has been called the most profound discovery of science. One of your strengths is explaining challenging concepts so that they're understandable to non-scientists. Would you explain the details of the test experiment that supposedly proves the violation of locality, your opinion of the test and the result and how that fits into the many-worlds concept?" I don't think it's actually very complicated. Bell's inequality just says, Imagine that you have two sets of observations that are separated, okay, so there's space like separated, they cannot signal back and forth to each other, and in the back of your mind, you have something like two entangled particles and you're gonna measure them in some axis up or down.

2:11:45.5 SC: But not always along the same axis, you're gonna measure them at different angles. And what Bell noticed is that in quantum mechanics, because of entanglement, these things could be really highly correlated, okay? Now, classically, they could be correlated also, but given things like the uncertainty principle and so forth, there's an upper limit on how correlated they could be if there was no wave function that spread across the distance, right? If there were only objects with definite values at different locations of space, there's an upper limit to the amount of correlation because you're not... You're not specifying ahead of time and what observation you're gonna make it, you can always just say like, I pick a particle that is spin up and I know the other one is spin down, but if it's just classical, then yet... You need to tell me what happens if I measure it along a different axis. In quantum mechanics where there's a superposition, you have a very definite answer to that, but you have to invent some theory for what is going to be the measurement outcomes if you measure it along a different axis, and what Bell proved is that that theorem can never be as correlated as it would be in quantum mechanics, because of the fact that in quantum mechanics, the wave function spreads across these two particles, even though they're very, very far away.

2:13:03.1 SC: So that is interpreted as evidence for locality, but look, as I said before, I think many-worlds is right. So to me, this is not a profound result at all, it's a very simple consequence of the fact that the wave function describes the world. Bell's theorem seems very profound if you were going to doubt that the wave function describes the world, wave functions are not local, that's just how they are, they describe what is going on all over the place at the same time. Okay? It's profoundly non-local. So if you already thought that quantum mechanics was many-worlds Bell's theorem is... You're given Bell's theorem, you go, "Yeah, sure." That's not extra profound, it is already part of the profoundness, 'cause I already believe that the wave function is the whole thing. There you go.

2:13:48.4 SC: Perry Ramwelski, says, "I often tell people that if you re-wound time, all the things that happened would still happen in the same way. Recently a friend pushed back and said it wasn't correct because of Heisenberg uncertainty principle. I think that's a misunderstanding of the uncertainty principle. Which of us is correct?" It's not the uncertainty principle, for sure, that's not what is going on as we already discussed, the uncertainty principal before, but it's actually a difficult question to answer because as many... As often it happens for these questions it depends on your favorite formulation of quantum mechanics. So if you are a Copenhagen quantum mechanics person, then no, what would happen if you re-wound the world would not be exactly the same because there is a truly random element in the laws of physics.

2:14:34.7 SC: Okay, when you observe something, it truly collapses in an unpredictable way, likewise in objective collapse models that have nothing to do with observers, like there are GRW models and Penrose's models and so forth, where the wave function really does collapse randomly. And if you thought that was the be-all and end-all of the laws of physics, that if you re-wound the tape it would not play the same thing. Now in something like a pilot wave theory in Bohmian mechanics that is deterministic, okay, but the determinism is governed by some hidden variables that you don't have access to. So if you re-wound the tape starting with the same values of the hidden variables, then indeed you would get exactly the same history played back. And then as usual, many-worlds is in this middle position where the wave function of the universe evolves in exactly the same way. But there's many, many universes right, there's many, many copies of the Universe, and it's not clear what you mean when you say, my universe would be the same, there's a lot of universes and they'd be different from each other. One of them would be the same as yours. The other ones would be different, okay? Nowhere in any of those words did I mentioned the Heisenberg uncertainty principle, because this all has to do with measurement, which as I said before, isn't about the uncertainty principle.

2:15:51.1 SC: Tim Ryan says, "How is the bass playing going? Have you explored any music theory, it can be very fun and rewarding." Yeah, the bass playing, was going really well before I went to Boston for my sabbatical in the fall, and I didn't bring the bass 'cause I was trying to focus on other things, and since I've gotten back, I've just been swamped with other stuff, it's really... I have too many things on my plate right now and part of the reason why this AMA is a little delayed. So I fallen off on the bass playing. I was playing it every day, at least a little bit, and it's not like that anymore. It is fun and rewarding. I like doing it. I wish I had more time to do it. I have every intention in the world of finding more time to do it at some point in the future, I'm not quite sure what that point will be.

2:16:32.1 SC: Tom says, "I really enjoyed the Arvid Ågren episode on the Gene's-Eye View of Evolution. In your experience, does the I would die for two brothers or eight cousins rubric have explanatory power for how people treat others in the world? E.g. Is the lower degree of genetic overlap a primary explanation for the West historically devoting fewer resources to Sub-Saharan African... Africa than to other Eurasian populations?" I think that it's worth saying about that idea that you would die for two brothers or eight cousins, that our unconscious is not that good at math.

[laughter]

2:17:10.8 SC: So even if there's something to that motto, it's certainly not true that we really follow that at a careful quantitative level. Rather how I would interpret that is saying that evolution kinda trains us to favor our family and maybe even... Well, as is often true with evolution, evolution doesn't actually change our traits, right? The thing about The Selfish Gene theory, The Gene's-Eye View, that certainly is correct, is that what is passed on from generation to generation is our genome, the pressure, the selection pressure acts on traits that we have as organisms, but then the result of that is that certain genes get passed on to the next generations and other ones don't, so the genes that get passed on is going to... Are going to give us certain traits and those traits might be... Be a little bit more concerned with your relatives, right?

2:18:16.0 SC: But I don't know how genes would even be able to tune themselves to such a degree where they would say, care as much for your own life as for two brothers or eight cousins or anything like that. It's much more vague than that. So I absolutely think that that kind of selection helps explain why we are more likely to do things for people more like us, closer to us. I think as Nicholas Christakis said back in his podcast episode, we have a weak in-group bias, so all else being equal, we are going to draw a circle around people like us and people not like us and prefer the people like us. And that's true in many many ways, and that makes perfect evolutionary sense, but I wouldn't get too precisely quantitative about it.

2:19:04.1 SC: Paul Turek says, "Gary Marcus said that for an AI have common sense, it needs certain mental faculties we have including to quote him "a cost benefit system", which I think is innate. You seem to agree or at least not object. Yet in your May AMA, you question questioned the idea that an AI will have values. You were replying to a question about Stewart Russell's argument that AI presents an alignment problem because AI's values might not align with ours. Have you changed your mind about whether or not artificial general intelligence will probably have values?"

2:19:34.9 SC: So the point I was trying to make is that, I mean, an AI will act in certain ways. Okay? And that the way that the AI acts can certainly be accounted for in terms of a cost-benefit system. The point I was trying to make was that that kind of cost-benefit system that the AI might end up having need not be recognizable to us as a set of values. Okay? If I throw a rock outside the window, it falls down, but I don't say it values being down, it values being at a lower elevation, I say it's just following the rules of gravity, okay? So I'm open to the possibility that AIs will act in such a way that we could sensibly take the human-centered concept of values and apply them to AIs, there's no obstacle in principle to that.

2:20:23.1 SC: I just wanna be open-minded about it, I'm also open to the possibility that AIs will not be recognizable as things with values, they will be recognizable as things that do things, and that those things can be accounted for by cost-benefit analysis, but it may or may not make sense to talk about them as having values.

2:20:42.6 SC: Rosi Amed Ahmed says, "Why is Schrödinger's equation constructed such that it only has a time derivative. If time and space are essentially the same, why single out one coordinate?" Well, Schrödinger's equation is part of quantum mechanics, time and space being the same is a lesson that we get from relativity, and in quantum mechanics, as it was originally formulated in non-relativistic quantum mechanics, they were different, time and space. Schrödinger's equation is a formulation of quantum dynamics that does treat time and space differently. So you can ask, Is that incompatible with the lessons of relativity and the answer is yeah, it works... It did some work in there and this is again special relativity, okay, not general relativity. We're not talking about gravity, we're just talking about the speed of light being the speed limit and so forth. It's 100% compatible, but it's sort of spiritually intention, if that makes sense. What I mean is that whenever you write down a quantum mechanical state as a wave function in some frame of reference in a relativistic theory, so you have the standard model of particle physics that is a completely relativistic theory.

2:21:53.0 SC: I can pick a reference frame. I can say, "Here are my coordinates on spacetime, here's my reference frame", and with respect to that reference frame, I can construct a quantum state and it will evolve according to the Schrödinger equation. Okay, so what I've done is I have broken the manifest... Sorry, I've taken the Lorentz invariance, the invariance with respect to different coordinate systems, and I have made it non-manifest by choosing a coordinate system. This is what we do all the time. We choose coordinate systems all the time, but we know that that's just a choice that we made, then we describe what's happening in that coordinate system, but the underlying dynamics, if your dynamics are relativistic, they don't care. You could use a different coordinate system and get the same physics. Same thing is true in quantum mechanics, you could choose different coordinate systems, you would describe the quantum state differently, but it would still have a Schrödinger equation that evolved it forward in time. So that symmetry between space and time can be hidden by a choice that we arbitrarily make but no physical results depend on that arbitrarily choice that we made.

2:23:05.2 SC: Nicholas Walker says, "When is the book out Based on Biggest Ideas, and will it be e-reader friendly?" It's scheduled to come out in September of this year, 2022. It's supposed to be e-reader friendly, there's definitely going to be electronic editions. We are working hard to make sure the equations come out right. I am not there in the design department of whatever the electronic book seller is or anything like that, so I'm not the one to complain to if they don't, but we're trying. We certainly want it all to be operational. It's a challenge that my publisher who publishes trade books is not used to, but they recognize the challenge and they're working hard at making it all work.

2:23:49.9 SC: Claudio says, "I thought I had an understanding of the cause of Hawking radiation from black holes. However, lately I heard some conflicting versions that made me realize that my version, pairs of particles popping out into space, one of them falls into the black hole, the other falls in another direction is pure BS. Can you give us an updated no clickbait explanation for the origin of Hawking radiation?" So I wouldn't say that that's pure BS, in fact, that explanation you just gave pairs of particles popping out into space has also been given by Stephen Hawking in his popular writings, right? So he knows what the real explanation is, but it always depends on what you mean by real or correct, 'cause there's different levels here. Okay?

2:24:32.8 SC: Here is a set of statements that are true and they may or may not satisfy you. If you have a black hole and there are quantum fields, so you're in a world that has quantum field theory and there's a black hole configuration, then, if you imagine converting... Exchanging that black hole for a slightly smaller black hole plus some outgoing radiation, that configuration, slightly smaller black hole plus outgoing radiation, has all of the same conserved quantities, same energy, same angular momentum, same charge and whatever. And a higher entropy. Okay, the conserved quantities are important because you'll never get evolution from a state with one electric charge to a different electric charge or something like that. But within the configurations at the same conserved quantities, you expect physical objects or whatever you want to call them, to evolve into states of higher entropy, and that's exactly what the black hole is doing. Okay? There you go. That's a reason to expect the black holes should evaporate, should give off radiation.

2:25:37.9 SC: It's not quite the physical mechanism beneath it, if you want to understand the that physical mechanism beneath it, and you don't... And you correctly think that the story about pairs of particles fluctuating in and out of existence is a little bit too hand-wavy and clickbaity, you have to admit that there is such a thing as quantum fields. And quantum fields evolve with time, and this statement of particles and anti-particle pairs popping in and out of existence is a colorful metaphorical way of expressing the fact that quantum fields live in superpositions of zero particles, one particle, two particles, etcetera. And the particular superposition of the quantum fields in the vicinity of the black hole event horizon is unstable, it tends to leak out particles, the existence of particles outside the black hole grows with time, and the size of the black hole shrinks with time under evolution according to the Schrödinger equation. If you wanna know more details than that, then you need the math, then you know, read Hawking's paper or read a good text book on it, you really gotta dig into it, but it is exactly what is predicted by the theory of quantum field theory in curved spacetime, there you go.

2:26:53.9 SC: Matt Hickman says, "What do you think the odds are there's an extinction level event for humanity in the next 100 years? Do you think we're doing more or less enough to prevent such a thing, or should we be doing more?" Well, I think there's different kinds of extinction events, I think extinction level event is hard to imagine, honestly, it's not zero certainly, but even a major thermonuclear war wouldn't be... Wouldn't render humanity extinct, it might wipe out advanced technological civilization if it were bad enough, but it wouldn't render us extinct, maybe it would be so catastrophic that 100,000 years in the future, we would all have died out, so maybe you'd count that as an extinction level event. But mostly, I think that... I'm more worried about really bad events that are not quite extinction level. Like if only a million people died, I think that would be bad. If 100 million or a billion people died, that's all the worse. Right? So I think we should worry more about those events than probably we do.

2:27:57.8 SC: And, it's easy to understand why. Human beings are just not meant, not built to appreciate risks that occur on time scales longer than a human lifetime. Right? So there's a 1% chance of a billion people dying because of some event per century, things that happen once per century, are just not things that human beings are good at preventing, we're not even good at preventing things that might happen next year. Right? So I do think we could be better at worrying about nuclear war, biological warfare, accidental or terroristic use of nuclear weapons and biological weapons, big solar flares, terrible pandemics, things like that, asteroids hitting the Earth. Asteroids are actually a pretty small number, but again, it's pretty cheap to worry about it compared to the other ones, so I do think we should be doing more, but it's not like a huge amount more, it's not... I don't think we need to spend large fractions of our GDP worrying about those things, we need to spend a small but prudent fraction on them.

2:29:04.2 SC: Eric Chen says, "What is the largest cardinality of infinity used in modern physics? Do infinite sets with cardinality greater than that of the real numbers have any use in physics?" So you may have heard, for those of you who are not experts, that there's different levels of infinity, the number of integers is infinite, but it is less than the number of real numbers, which is a bigger Infinity, and which Infinity we're talking about is the cardinality of the set. And there are bigger infinities than the number of real numbers.

2:29:33.8 SC: So roughly speaking, Eric, physicists don't care about this stuff at all, that to a first approximation, the difference between different kinds of infinity is just irrelevant to physics. Now, there are certain corners of physics where they're a little bit more mathematically careful, where countable versus uncountable, namely integer level infinities versus real number level infinities do matter to them in certain corners of mathematical physics, especially quantum field theory and quantum mechanics. So they care about those things, but there's no experimental difference, there's no empirical result, it depends on whether or not the reality of the situation is countable or uncountable, as far as I know. Beyond uncountable, beyond just the number of real numbers... The cardinality, of real numbers, I know of no use in physics, but maybe I wouldn't... Maybe there is some in some deep, deep corner of mathematical physics that I'm not aware about, but anyway, it does not percolate into most working physicists consciousness.

2:30:35.7 SC: Pete Faulkner says, "Listening to your Wondrium course on time, and I heard you talk about CPLEAR, which was an experimental particle physics experiment, and the demonstration of time asymmetry in the weak force. Could this time asymmetry be in some way an explanation of the matter-antimatter asymmetry we see in the universe?" Well, it could be related, but it's probably not the explanation for two reasons.

2:30:57.4 SC: Number one, what we see in the experiments like CPLEAR, which looks at kaons and antikaons, that's a time reversal invariance violation from the standard model of particle physics. And that violation just numerically seems to be too small to play an important role in explaining the matter-antimatter asymmetry in the universe. The other point is that to explain the matter-antimatter asymmetry as Sakral pointed a long time ago, you need more than just time asymmetry, you need time asymmetry, Baryon asymmetry, kind of obviously, and you need departure from thermal equilibrium and need you them all in the right place at the right time, working together in the right way. So it's impossible just to point to one of those violation of time asymmetry and say, "That's why there is this difference between matter and anti-matter." You need all three at once, Baryon symmetry, time asymmetry, thermal equilibrium violation. Maybe you have that in your universe, probably you do, since there's more matter than antimatter in the universe, but we don't know which of the many, many specific scenarios for that asymmetry is the right one right now.

2:32:08.4 SC: Oleg Ruvinsky says, "You mentioned in the past that you love Iain Banks's Culture series, what are your favorites in it and why?" I think my favorite is Excession actually, I can never... Look... I'll be honest, I don't think that his titles are great, so I can never remember which plot goes with which title of the books, except for like easy ones, like The Player of Games, but Excession is the one that places the most emphasis on the minds... These giant AI spaceships, they're talking to each other, telling jokes and everything. I just like that. That's why it's my favorite book, that's a kind of a cheap answer, but there you go.

2:32:44.9 SC: Rob Greyber says, "You recently had two podcast guests who talked about language, specifically the mathematics and analytics underneath human vocabulary, language and stories. Number 174 with Tai-Danae Bradley and number 181 with Peter Dodds. Listening to both episodes, it seems Bradley laid out a theoretical explanation of language and Dodds does a sort of experimentalist application of some kind of approach like that. I'd be curious to hear your thoughts on this field of study generally. Is this analytical study of language and stories just a descriptive exercise about an emerging language of our culture, or does it have some power to help us understand what deeper General AI, for example, might look like?" I'm not quite sure if I understand the two options here, they seem both completely compatible to me, it can be a descriptive exercise about an emergent aspect of our culture and have the power to help us understand what deeper General AI might look like. Emergent aspects of culture or anything else aren't arbitrary, there are reasons why certain things emerge and certain things don't. So the fact that we use language in certain ways that the entropy that we can assign to different words or phrases or sentences has certain structure, certain patterns, this is not arbitrary.

2:33:58.6 SC: There are reasons why it is like that, so it... Both is a descriptive exercise trying to understand how we actually talk, the information that is conveyed, how we use language to sway people, make persuasive arguments, toy with people's emotions, and also give us some insight into how AI might itself use language. Like I said before, it would be a little bit presumptuous to imagine that AI is just like us, I especially think that... I forget whether I've talked about this on the podcast or not, but the fact that artificial intelligences are generally these days, not embodied, they don't have bodies, they're just in software, and they certainly don't have the kind of complicated biological bodies that you and I have, I think this matters a lot. I think our bodies are crucially important to making us who we are as human beings, we are not just software that is working on any different machine that you wanna run it on, but... Okay, aside from that, I do think that there's probably regularities and similarities in how general intelligences will speak to each other, but I'm open, I'm willing to do the experiment there too. So it's... If we find ways that human beings use language that can be mathematically studied, it's a hypothesis to say that AGI will also have those features and then we can go test that hypothesis when we actually get it.

2:35:25.1 SC: Phil says, "Is there a deeper reason why quantization works so well? Why would replacing classical observables with operators give such good results, or maybe I should ask this the other way around, since quantum mechanics is more fundamental." Yeah, in some sense, you should ask it the other way around. The question is, we have quantum mechanics, why is there a good classical limit? Okay? And that's a non-trivial question. Again, one of the recent papers that Ashmeet Singh and I wrote together is pointing in the direction of answering that question. Other people long before us have thought about it, why and under what circumstances is there a classical limit to quantum mechanics, but there is... But your question is actually a little bit deeper than that, because even if there were a classical limit, even if you have theory A and under the right circumstances, there is a limit to that theory that looks like a different theory theory B, okay? The question we're asking here is, how can you ever reconstruct theory A just given theory B? Reconstruct the full theory from the limit. In principle, there's no reason at all why you should be able to do that. To me, the limit might only give you a tiny hint of what's going on in more general circumstances.

2:36:36.6 SC: So that's why I think you shouldn't expect that every single quantum theory... In fact, it's certainly not true that every single quantum theory comes about by quantizing a classical theory. The weird thing is that in our experience, we've done pretty well in finding out what the quantum theories of nature are by starting with a classical theory and quantizing it. That's the weird thing, why are the theories that work for us in that particular class of theories where you can reverse engineer the full theory from the classical limit? That I have less strong ideas about, I'm really not sure why that is true. Maybe there's a good theory for that, and of course, I also think it's failing in the case of gravity, so that's... That would have to be a thing to consider when you're inventing the explanation to this puzzle.

2:37:25.4 SC: Voler O says, "A bit of a dark question, but would you rather survive a nuclear exchange or be amongst the first to go?" I think it's pretty easy to say I'd rather survive, right? Yeah. Most of human history, times were tough, times are still tough for many people right now. The fact that you live in these circumstances where times are tough does not take away my motivation to live and try to make things better. In fact, you know, it's easier to know what to do to make things better when times are really, really tough, 'cause you just have to make people survive and help out each other. And I would want to be around for that.

2:38:00.3 SC: Robert [2:38:00.6] ____ says, "In my system of values, my moral system, I think everything is acceptable as long as no suffering is brought by that action, suffering is what gives an act its moral worthiness. However, using this framework brings me to a very taboo situations for most people, like the situation where a pedophile is satisfying his or her sexual fantasies doing during a video chat with a parent who bathes their baby, let's say. The parent gets the money, the pedophile get sexual satisfaction without hurting anybody, and the baby is just completely unaware of anything like this happening. In my own system of values, this whole situation is not immoral, I've been trying to analyze it to see if I'm making a mistake anywhere, but I don't see anything wrong with it. However, most people would be appalled of my conclusion and think I'm insane. Do you see anything wrong here, is there any argument I could use to come up with a conclusion of this situation is wrong?"

2:38:45.8 SC: So I think that the situation here... There's two things going on. One is that sure, many people's morality comes very much from instinct rather than from a well-worked out rational system, and that's not even necessarily a bad thing. It's not ideal. I would prefer if everyone were completely rational, but I don't think that as I've often said that morality is a simple matter of just being rational, you need some starting point and your intuitions, your inner feelings are the starting point. I think that morality comes about by starting with some moral inclinations or intuitions that we have and trying to make them into a rational system, I think there's a mistake to be made by inventing a rational system and then saying that even though this disagrees with my intuitions, I nevertheless. I'm gonna stick with the system, 'cause the whole point of the system was to systematize your intuitions.

2:39:42.6 SC: Okay. But that's one aspect. The bigger aspect that you're asking about is, are there arguments that you're not considering that might make this situation immoral or moral rather? I can imagine there would be situations like this in some very, very broad sense, which I think could be perfectly moral, the particular one that you're writing about, I think it's pretty easy for me to see where it could be argued to be not moral.

2:40:08.9 SC: I think that the basic lesson is that it's a little bit too simple to do philosophical thought experiments of this form and neglect features of the real world and features of the real world matter in these circumstances. In particular, both the parent and the pedophile in this circumstance, you have to be sure are not going to do anything that actually does cause harm to people. I mean, it's a little bit weird for a parent to be pimping out their baby to give cheap thrills to a pedophile and imagine that the parent doesn't do anything else that we might find objectionable. I think that's gonna be the origin of a lot of people's worries there, but more importantly... And this is really the heart of the matter to me. I don't think it's fair to say the baby is just completely unaware of anything like this happening. I think that it is okay to be troubled by things you would think are bad even if everyone is unaware of them.

2:41:08.0 SC: Right? And in particular, in the case of this baby, maybe they will grow up and find out about it and be very, very disturbed sometime in the future. You can certainly not know for sure that that won't happen, right? So it's just much easier, safer, a better moral choice to not put the baby in that kind of situation where the baby has no agency to give consent for anything like that. So to me, that kind of argument is a perfectly good reason not to allow something like the situation you're talking about.

2:41:42.4 SC: Steve Pilling says, "What do you think of the black hole as fuzz ball or ball of string model? It seems to avoid problematic issues with the singularity where Sir Professor Roger Penrose says that space and time come to an end." You know, I don't know a lot about it. I've tried to understand it. For those of you who don't know, there is a model that is most associated with Samir Mathur of Ohio State University, where he tries to... Let's put it this way, if you think that information gets out of black holes eventually, if you think that the laws of quantum mechanics are purely information conserving, including processes such as black hole evaporation, and you think that String theory is the right theory of the world, then you need to believe that black holes can be described in the context of String Theory in a way that is perfectly happy to just obey the Schrödinger equation for evolution, right?

2:42:36.8 SC: There have to be a set of degrees of freedom in Hilbert space that interact with the outside world, etcetera, etcetera. Then the question becomes, what are those degrees of freedom? How do we think about them? And so, Mathur has described a way, or proposed a kind of way to think of the black hole as a fuzz ball, as a set of strings that are sort of tied up together and wound up in different ways. My impression, and I've tried to understand this and not quite succeeded, because I think that in part... 'Cause no one understands it, in part because of my limitations, but it's not a complete description. So, Samir is able to describe what would happen in certain very, very, very special circumstances of, you know, perfectly extremal black holes in supersymmetric situations, etcetera, but not give a completely generic understanding of an ordinary black hole that you might find in our galaxy or something like that.

2:43:30.1 SC: So it's hard to know what to think of the proposal, 'cause I don't think it's fully fleshed out yet, or maybe it has been since I last paid attention to it, but that's my impression. I do think that the general idea has to be on the right track, again, if you think that information is conserved coming out of black holes, which I think is likely, but I'm not 100% wedded to it. There have to be some degrees of freedom in there, it's almost like, I don't see how you can object to it, [chuckle] right? I mean, people sometimes read about this and they're acting as if they're translating it as if there's not really a black hole, because instead there's a bunch of strings behind the event horizon. That's just not the way I would think about it at all, it's saying that what is behind the black hole is a bunch of strings, you know? It might be perceived to an in falling observer just as ordinary space time inside a black hole, but in String Theory, the world is made of strings.

2:44:22.3 SC: So, there's a specific configuration of those strings that makes up a black hole that is different than the configuration you find that makes up empty space or the Earth or something like that. So, something like that, even if we don't know the details yet, is gonna have to be true, if String Theory is on the right track.

2:44:41.4 SC: Ezra Parzybok says, "What are your thoughts on preppers or prepping for a disaster, personally?" You know, nuanced thoughts, I hope. You know, I'm in favour of being prepared for disasters. Look, I live in Los Angeles, there are real disasters that happen around here, whether they're brush fires or earthquakes or mud slides or droughts or whatever. So we are not very well prepared for that kinda thing, but we have our little earthquake kit, okay? You know, we have some water and some food and first aid stuff, flashlights and things like that. That makes perfect sense. I mean, why would anyone object to preparing for potential bad things happening to you?

2:45:20.5 SC: Now, of course, the answer to that, why would anyone object? Is that some people take it too far. They fetishize the idea of preparing for disasters that are extremely unlikely. There's a bigger discussion to be had here about the whole way we think about really bad possibilities that happen rarely, right? A low probability event, but it would be really, really disastrous. This goes back to questions we've already talked about in the AMA. I think that those kinds of questions are intrinsically difficult. I don't think we have a well-formulated clear theory of how to deal with them, and the reason why is because it's not just a matter... Let me put it this way, when you have things that are of fairly ordinary probabilities between 1% and 99%, let's say, and the consequences would be pretty bad or pretty good, but not overwhelmingly good, not like end of the world or ascend to heaven kinda stuff, but somewhere in between. And then roughly speaking, you can multiply the probability by the utility plus or minus of that event happening and work on the basis of that, okay? And be kind of a consequentialist about the whole thing.

2:46:29.8 SC: When the probabilities become 10 to the minus six, or 10 to the minus 12 or something like that, but the consequences become cosmically good or bad, it's no longer just a matter of multiplying the probability by the utility. Because maybe there's an error bar on your probability, right? You don't really know. And who knows what the space of possibilities is. You know, I love this... One of the gems of wisdom I took from the podcast interview with Martin Reese was in the context of the Large Hadron Collider turning on and potentially swallowing the Earth, right? And physicists worked out all the probabilities and they said it's possible, but it's very, very, very unlikely. And people said, "Well, it's destroying the Earth, even if it's possible at all, you shouldn't do it." And Martin Reese's response was, "Well, it's possible, but unlikely that you get free energy forever," perpetual motion machine, out of science that comes out of the LHC. It's possible, unlikely, but possible.

2:47:29.2 SC: And the point is that the space of very, very unlikely events is something that we don't have a good handle on, plus or minus. So anyway, this is getting far away from the preparation question, but I wish we had a better set of rules for being rational in these cases of extreme uncertainty and extreme risk combined together. And that's kind of what is going on in the prepper community, where they really... Yeah, there are people out there who treat prepping for a big natural disaster as something like that should take up an hour a day of your time, [chuckle] which is probably way more than it deserves, honestly. So there's some happy medium in there to be found.

2:48:14.1 SC: Okay, Holographic Cosmology asks a priority question. "We use two eyes to focus on one object's position to create the illusion of depth. We didn't always have this ability, it had to evolve. Is it possible that we're looking at space wrong, could we be missing depth or other information that we need two or more eyes capable of looking in two different positions at once in order to find?"

2:48:35.0 SC: You know, never say never, I would say, but my strong feeling is no, that we're not missing something analogous to depth in the same way. And the reason why is because we've gone far, far, far beyond what our two eyes can tell us about space. We understand a lot about space, we're able to do experiments in it, the inverse square law, behavior of gravity and electromagnetism depends crucially on the fact that space is microscopically three-dimensional. There's many, many pieces that go into our current understanding of space, any one of which would go wrong, if we were missing something dramatic, like a whole new sense of depth or something like that. So, our eyes were really useful back in the day, but we're not dependent on them in the same way to get our best scientific image of the world these days.

2:49:22.5 SC: Lewis B says, "Following up on the previous answers regarding falsifiability as a criterion for science, in a beyond falsifiability world view, where does the hypothesis of a supernatural God fit philosophically? I know you consider it a bad hypothesis, but is it a scientific one? The supernatural and Gods are typically dispensed with as non-scientific because they are non-falsifiable, but it wouldn't seem... But it would seem you don't have this luxury. Is positing a God somehow less scientific than hypothesizing what is beyond the edge of the observable universe or inside a black hole?" So two things, one, I think you should read more carefully [chuckle] or read the paper I wrote on beyond falsifiability, 'cause the point is not that there was some idea that we agreed on that scientific theories need to be falsifiable and we're changing that idea. That is not what's going on.

2:50:14.2 SC: What's going on is that there was this idea from Popper that involved falsifiability as a demarcation criterion between scientific and non-scientific, and it never was accepted. Philosophers of science never had a period of time where most of them were onboard with this idea, because it turns out that demarcating science from non-science is more subtle than that. But at the same time, they were appreciative of what that idea was trying to get at. And so, it's not a matter of saying, "We don't need falsifiability anymore." It's a matter of saying, "Okay, falsifiability is a step in the right direction, but we need to do better," and we're continuing to do better, that's the beyond that we're talking about in this sense. We want theories that are empirically judged, and want theories that are definite in what they say about what happens in the universe.

2:51:04.2 SC: Okay. And as far as that is concerned... So the reaction in my paper is not against Popper, who is just a step in our understanding, a better and better understanding of how science works, but against scientists in the current era who misuse Popper by being lazy, you know? They think that there's a motto that they can put on a bumper sticker that tells them what a theory is scientific or not, and that's just not... The world is just not that simple. [chuckle] It's a little bit more complicated in that. Sorry. So those scientists need to do better at their philosophy of science. And likewise, there's a whole bunch of atheists who are similarly subject to over-simplifying things to get where they wanna go. They wanna go to the result that you shouldn't take theism seriously. And so, they say, "Well, it's not like a scientific theory, it's not falsifiable, therefore we shouldn't consider it." You've never heard me say that. I think that that is lazy and silly to say those things, okay?

2:52:05.2 SC: That's why as I said before, I had a talk saying God is not a good theory. It did not say God is not a theory. God is a perfectly good theory, it's a statement about the ontology of the world, saying that there's more than just the physical in the world. Okay? And we should judge that idea about the physical world, how? In exactly the same way that we judge any other scientific theory, one way or the other. We ask what predictions it makes, what we should expect if it was true, and we compare those predictions against the world in which we live. Okay? So I don't see any problem. I've never said that supernatural or Gods are non-scientific. I think the whole idea of what is called methodological naturalism, the idea that science starts by assuming natural explanations for phenomena, 100% wrong, that is a totally bogus, okay? What science is, is methodologically empiricist.

2:53:02.4 SC: It judges things by the predictions that those things make for the world. So I think that God makes predictions. I think that if God existed the world would be a very different place, it would be very, very noticeable if God existed. That's the whole point. That's why it's not a very good theory.

2:53:18.1 SC: Kathy Seager says, "Michael Dine wrote in his new book about Weinberg's weak anthropic principle. Just to explain the cosmological constant would require an absurd number of different universes, 10 to the power of 120 at least. But far more of other constants in nature are fixed this way. And he wrote, such a mode for explaining the world around us is just too much to swallow. Would you as a person not try invoking a huge number... A huge amount of worlds in quantum mechanics, be as hesitant as Dine regarding the multiverse?"

2:53:45.3 SC: So I actually... I mean, I read Michael's book, but I don't remember that exact line 'cause... I know this stuff pretty well. I skim sometimes, okay? When reading popular physics books. But I know that Michael Dine takes the anthropic principle totally seriously himself, including the necessary number of universes. So, he might have been either describing a point of view that he temporarily had or maybe describing the point of view of skeptics of the whole idea, but he's absolutely willing to consider this many universes. Personally, when you say statements like, an absurd number of different universes, I don't know how to respond to that. And what counts as an absurd number of different universes? I recognize the difference between one universe and two universes, [chuckle] you know? If you can get away with just one universe that would be better. I mean, in favor of that, all else being equal, but I don't think you can all else being equal, I think you have to make certain sacrifices that are too far to go in order to make that happen.

2:54:45.2 SC: But once you have two, [chuckle] then there's no difference in my mind between two and 10 to the 120, or 10 to the 10 to the 10 to the 10 to the 10 to the 120 factorial, like, who cares, it's a number, it's a big number. Don't worry about how it considers... How it sounds to be absurd or ridiculous to your puny little human brain. I don't think that's something we should worry about that much.

2:55:06.3 SC: Anita Tomasik says, "Does state of thermodynamic equilibrium of the universe in which does a state of thermodynamic equilibrium of the universe in which time's arrow no longer exists, affect in any way our four-dimensional structure of space time?" I doubt it, but I wonder how it looks like highly hypothetically, from a God-like point of view perspective of the block universe?

2:55:30.6 SC: So, I think the answer is no, if I understand the question correctly. If the universe were in thermal equilibrium, four dimensional space time would still be four-dimensional space time, except there'd be no arrow of time. So I always try to distinguish between time as a coordinate on the space time and the arrow of time, which is the feature of the behavior of matter and stuff in the universe, which differentiates the past from the future. You know, there's no arrow of space, if you're out there in space, floating between the planets, there's no difference between up, down, left, right, forward, backward. But there is space, space still exists, you don't need an arrow for something to exist. See, arrow time a feature of time, but it is not time itself. So time would still exist in thermodynamic equilibrium. In particular, if you just imagine a box of gas as a simple model, right? As we like to do, when we do thermodynamics thought experiments. If you had a box of gas in thermodynamic equilibrium, the macroscopic features of the box of the gas in the box do not change with time, you're in equilibrium. But microscopically, the particles are still moving, there's still time evolution there. So time and space would still exist in the ordinary way.

2:56:44.0 SC: Herbert Berkowitz says, "I recently saw a reference to a particle called the antineutrino." That is true. In fact, you've seen references, you've heard references earlier in this podcast. "That stopped me in my tracks, how can a particle with no charge possibly have an anti-particle that will obliviate it?" So there's a short answer to this and a longer answer to this. The short answer is, it doesn't... A neutrino does not have electric charge, but a neutrino does have lepton number, and the lepton number can be positive or negative, and the lepton number is conserved. That's why in this example of... So I had to... It took me a while to get it right there.

2:57:21.0 SC: But when a tau decays to a muon, okay? So a tau has tau number, as well as lepton number. A muon has mu number, as well as lepton number. So if a tau turns into a muon, the lepton number is the same, the electric charge is the same, but tau number suddenly changed to muon number, so that can't be right, 'cause they're both conserved, at least as far as we know. Therefore, you need to have tau number carried away somehow, and it's carried away by a tau neutrino. But that gives you extra lepton number, so you need to get rid of the lepton number to cancel it off and also to cancel off the extra muon number, and you do that by adding one anti-muon neutrino. And this is what is actually happening when you go into the details. I did a lot of this in my Higgs Boson book, The Particle at the End of the Universe, if you're interested.

2:58:15.3 SC: So, a tau actually decays into a muon, a muon antineutrino and a tau neutrino. The longer answer is the word obliviate bothers me a little bit there, because this idea that every particle has an anti-particle that is defined by the thing that annihilates it, is way too simplistic. What there are is a bunch of particles, they interact, and all those interactions are in accord with the symmetries and conserved quantities of the standard model of particle physics. It is convenient to separate particles into particles and anti-particles, but it is not a fundamental feature of nature. The existence... The fact that there is a fundamental... The fundamental feature that exists, is that certain kinds of particles that have quantities like spin, like a neutrino has, better have anti-particles, unless there is some fundamental breaking of the symmetry.

2:59:10.6 SC: Well, let's put it this way, once you have spin, you can imagine anti-particles, you don't need to have... Now, I'm hesitating, 'cause there are Majorana theories of neutrinos where you could have some kinds of neutrinos without anti-particles, but that's a whole different complicated kind of thing, which proves my point. My point is that there's not a simple distinction into particles and anti-particles in nature. I mean, photons, right? Photons, do they not have an anti-particle or are they their own anti-particle? The real answer is, it's more complicated than that. The anti-particle particle distinction is not the be-all and end-all of this way of talking.

2:59:45.0 SC: Peter Bamber says, "I understand that in general relativity time is not absolute, that the passage of time at different points in space varies because of mass energy densities between and around the points. I've also heard it said that in quantum mechanics, time is a fixed backdrop along which wave functions evolve. Are these views incompatible? And if so, is this one of the reasons why GR and QM are difficult to combine in a single theory?" So, I'm gonna say no to a bunch of things here, and it's not your fault, Peter, you've been misled by the world. It's not true that the passage of time at different points in space varies. The passage of time is always one second per second, it is never two seconds per second. I don't even know what that would mean. The true fact in relativity, whether special or general, is that there can be different amounts of time elapsed if you take different paths between the same two events.

3:00:35.4 SC: So in special relativity, that happens because one path is sort of curvy, you zoom out there in a spaceship and zoom back, and the other one is straight. Whereas in general relativity, they can both be pretty straight, as long as one of them hangs out in a strong gravitational field. Sometimes this set of words is sort of mangled into saying that the rate of time flows differently at different points, but I think that's just a bad way of thinking about it. Having said all that, as far as quantum mechanics and gravity are concerned, this is related to a problem, but this is not the problem, you know? In general relativity, there is no obvious choice of time parameter in the same way that there is in special relativity or in... Well, in Newtonian mechanics there's a perfectly obvious choice of time parameter, 'cause there's only one. In special relativity, there is a set of different choices you can make depending on different inertial reference frames, but they're all on an equal footing, they're all equally good for whatever problem you want.

3:01:33.2 SC: In general relativity, there's an infinitely bigger set of different things you can use. But again, they're all fine, you know? People in general relativity talk about many fingered time, so time can sort of... You can move your slicing of the universe in different ways in different regions. It's all fine. That's not really one of the fundamental issues in quantum gravity. It's closely related to a fundamental issue, which is called the problem of time, which is that if you just naively quantize general relativity for a closed universe with zero energy, like we were talking about, there's no time evolution at all in that theory. So you have to get time being emergent. And you can try to do that. It's tricky. There are details. That's for a whole another podcast maybe.

3:02:18.9 SC: David Boardman says, "Is there a way to describe what a low entropy universe at the time of the Big Bang looks like compared to a higher entropy situation?" If by the time... If what you mean by the universe at the time of the Big Bang is a very hot, dense, rapidly expanding state, the thing that makes it low entropy is that it is extraordinarily smooth, right? It's homogeneous, the same amount of stuff at every different point in the universe to a very good approximation. That is not what you would expect in a high entropy state, because gravity is really, really important, right? If you have a bunch of particles in space and you just let them evolve under gravity, they will come together, they will squeeze together and then become more inhomogeneous, they will not even out, because gravity sort of works in that direction. So a high entropy version of the early universe would have been wildly fluctuating from place to place, not at all small. That smooth... Not at all smooth. Sorry. That smoothness is the crucial ingredient.

3:03:20.8 SC: Samuel Benjamin says, "I've noticed from your books and podcasts that you like to use the term loosey goosey." See, now you've... Now you told me that I like to use that, now I'm never gonna use it again. I'm gonna be self-conscious, but okay. Probably you're right. Samuel continues, "Please can I get a shout out for my cats, Lucy and Goose, they're sisters who we've had since eight weeks old. Lucy is a more conventional cat in her behavior, whilst Goose is I think more like Ariel. She likes to lie in her bath after it's drained, much like Ariel's morning shower routine." So, shout out to Lucy and Goose, how you doing L and G? "What are your thoughts," Samuel continues, "on giving animals the same rights as humans? Do you think this would be sensible and/or practical?"

3:04:01.1 SC: So, at face value, if I just take your question as you've asked it, no, I think that'd be crazy, giving animals the same rights as humans. You know, ants are animals, I don't wanna give ants the same rights as humans. I don't want them to vote. I don't want them to be able to drive. There's a million ways in which I don't want to give animals and humans the same rights. Now probably, you're thinking about animals that are a little bit closer to human beings behaviorally or evolutionarily, like cats and dogs, or chimps or pigs or something like that. And I am a big believer that it's fuzzy, right? 'Cause there's no hard bright line there either between animals that deserve rights, and animals that don't, and there could be different rights that are deserved by different groups of animals. As I've sometimes mentioned before, to me, like the single most crucial thing that makes human beings special is the ability to, as a species, not every... You know, people can have brain damage and things like that.

3:05:00.0 SC: But as a species, we have the ability to conceptualize the future in a more intricate way than other species do. We have the ability to bargain on the basis of future rewards, to suggest hypothetical situations, to talk about them symbolically, make agreements with each other, contracts and all of that stuff. And that ability brings with it the ability to sort of be sad or be angry or be disturbed in some way, if our future is threatened, in ways that I don't think other animals have. Maybe they have some, and maybe I'm wrong, maybe future research shows that I'm wrong, in which case we update and we change our minds, but that's the most important thing to me. And I think that's an important distinction. All these distinctions are important. Again, I think that a statement like... I think the reality is gonna be much more complicated than that, and we need to understand and appreciate those complications and deal with them, roll up our sleeves and try to figure out what to do with them.

3:06:10.3 SC: Robert Henderson says, "My impression is that it's not necessary to get into quantum field theory on thinking about quantum theories foundational questions that non-relativistic quantum mechanics is sufficient. Is that so? And if it is, can you say why, given the questions around locality in the nature of space and time seem to be relevant to interpretation-al questions?" Well, again, yes and no. [chuckle] Is it necessary to get into quantum field theory? Look, quantum field theory is a version of quantum mechanics, okay? It's not a separate thing. It's not like the successor to quantum mechanics. It's a successor to non-relativistic quantum mechanics, relativistic quantum field theory, in particular, there's also non-relativistic field theories.

3:06:49.2 SC: But usually we take a shortcut and refer to non-relativistic quantum mechanics versus relativistic quantum field theory. And anyway, if there are foundational issues with quantum theory in general, those foundational questions matter just as much for quantum field theory and just as much for non-relativistic quantum mechanics. So, if you take the idea that non-relativistic quantum mechanics has a lot less sort of mathematical baggage that it carries around with it, then you can focus in on the foundational questions better by thinking about that context than you would in quantum field theory. Quantum field theory has its own special problems, there's extra infinities, as you may have heard. So you have to re-normalize and whatever, and when you get to the axiomatic level, it's harder to make sense of those theories, but those are separate theories that we normally think of as the measurement problem or the ontology problems of quantum theory in general.

3:07:46.1 SC: Now, as you say, there are questions about locality in nature of space and time that are common to the foundations of quantum mechanics and to relativity. So, maybe people are making a mistake by focusing on non-relativistic quantum mechanics. I think that they are making a mistake, but in a subtle and sort of sideways way. It's not that it's a mistake per se, to think about non-relativistic quantum mechanics, but non-relativistic quantum mechanics is formulated in a fixed spacetime background, the Newtonian spacetime background in particular. And so, I think it's just easy, too easy to sort of take for granted the structure of space-time that that set of assumptions gives you, rather than really thinking about what life would be like without that set of foundations to lean on, right? And so, I think that when people talk about locality...

3:08:43.6 SC: Let's put it this way, there's a lot of people in the world of the foundations of quantum mechanics who say... Make a big deal out of Bell's inequality and say like, "This is evidence for non-locality," and say, "this is the most profound result we ever have in the history of physics," etcetera, etcetera. Because it's violating locality and Einstein cared about locality a lot. And my attitude is, if you have quantum gravity, you certainly don't have locality, and you shouldn't have locality, you can't. If you think about a path integral, you're summing over many different spacetime geometries. There's no way to pinpoint a single point in space uniquely in all those different geometries at the same time. So the question is not, from my point of view as someone who cares about gravity and spacetime. The question we should be asking is not, "Oh, my goodness, physics is non-local, what are we gonna do about it?"

3:09:36.9 SC: The question we should ask is, "Why in the world does physics look local as much as it does since gravity, quantum gravity, anyway, clearly should not be local?" So that's a good question, I don't think we give enough attention to that. So in that sense, I think you're completely right. People are missing something by focusing on non-relativistic QM.

3:09:55.2 SC: Okay, the last question for today's AMA, for this month's AMA, Bagdin Navinaturu says, "Russia has never given up in the last 30 years since the collapse of the USSR in the hope that Europe should remain divided even against its will. It seems to me more than a war against Ukraine, it is a war against the free world, perhaps the most difficult test for democracy. Is it possible for people to understand what a valuable gift democracy is and to make us truly appreciate and protect it as never before?"

3:10:26.2 SC: So, look, I'm not an expert on Russian history or European history or Asian history or international relations or any of those things. So, anything I say as usual for a question like this, take with a grain of salt. But let me distinguish between two things going on here. Russia is not a democracy. You know, we live in a world where democracy has such good resonance in people's minds that even countries that are clearly not democracies pretend to be democracies. Ukraine really is a democracy. There's a little meme going around that drives this home, you know, who was the leader of Russia and Ukraine? And I think it was Belovo Russia also 20 years ago, 15 years ago, 10 years ago, five years ago now. For the Ukraine, it's different in every single segment, and for Russia it's the same in every single segment. That's the sign of not being a democracy. The opposition party never wins, that's what means you're not really in a democracy. Okay?

3:11:32.1 SC: In some very real sense, it is a threat to democracy, that a non-democracy like Russia can invade and conquer or attempt to a democracy like the Ukraine, and that is bad and we should fight against it. But the long-term way to fight against it is not to erect barriers to autocratic regimes invading democracies, but to not have any autocratic regimes, to spread democracy worldwide. So as much as it is in some sense a threat to democracy when Russia invades the Ukraine and as much as a tragedy it is in a lot of real ways, the things that worry me about democracy are not being invaded by autocracies, but internal collapses, right? There are plenty of countries that have been democracies and stopped being democracies. And there's no guarantee whatsoever that the United States or Canada, or Iceland or UK or France or whatever could not be one of those countries down the line.

3:12:28.8 SC: And part of it is that there are powerful populist forces that want to use rhetoric and technology and misinformation, and resentment and alienation among people who are not doing well in different countries to gain power in ways that have zero respect for democracy. There's no question for any fair-minded observer that the Republican Party here in the United States is much less interested in the trappings of democracy than it used to be. It used to be that as much as you might have disagreed, and I did disagree with Republicans on various political issues, we still stuck with the institutions of democracy fairly straightforwardly. You know, they would try to suppress votes by all means, but there was still some feeling that if the election went one way, you had to stick with it, right?

3:13:27.8 SC: And that's gone away and to a very large degree. Some large number of Republicans still don't think that Joe Biden won the election in the United States. That's the danger, and the real danger is that it's not just rhetoric that the people who think this way tried to overthrow the election. They sent in fake authorizations of electoral ballots to the National Archives to try to get on the record that Trump won the election in different states, even though he didn't. And they are now trying to take over state houses and judges and local election boards, so that if it happens again, they can get away with it. That's the worry that I would have about democracy, okay? I mean, democracy is falling... And this is just the one I'm familiar with, the United States. Obviously, other countries have their own problems.

3:14:21.4 SC: But democracies can very easily collapse from with inside. And furthermore, just to be fair, I don't think this is a both sides issue, it's not like both sides do it equally badly, but both sides have their problems. And to be in favor of democracy means to give up some of what you want, right? Because if you're in favor of democracy, you're saying that there's gonna be a majority vote and you're gonna stick with it even if you don't like it. Now, there has to be protection from minority rights, etcetera, and that's important, but to enter into democracy is to enter in the possibility that you will not get what you want. And there's just an increasing number of people of all political persuasions who just don't think that way anymore. They're not willing to make the effort to gain power by trying to persuade people who don't agree with them to go along with their policies, they wanna use some other mechanism.

3:15:17.3 SC: Democracy is hard. It's hard to make it work. And you know, again, you can be cynical and say, "Well, it's never worked," blah, blah, blah, fine, but it can work to different degrees, it can work more or less. And it's a lot less that we could have democracy here in the United States than we do right now, and I'm very worried that that might actually happen. What I am cheered by is, among other things in the world, I am just cheered by those Ukrainians. You know, I feel very bad for them, but those people are fighting for their country and for democracy and for their sovereignty, and they are doing so with enormous courage and in a way that just has garnered respect of the whole world. There's another footnote here, which is, of course, that we in the West tend to pay a lot more attention when white people are being attacked than when people of color are being attacked, so we do not give fair media coverage to these kinds of tragedies going on worldwide.

3:16:18.9 SC: And there are plenty of others other than in the Ukraine, but that does not take away from the tragedy that is going on in the Ukraine and the fact that their story has been very inspirational, and they brought together people around the world against the authoritarian regime that is trying to take them over. So, hopefully people start taking seriously... Yeah, some people obviously have for a long time, but more people start taking seriously the fact that democracy is not guaranteed, the fact that it's hard work, the fact that it requires persuasion and cooperation and compromise and coalition building, and you can't just stamp your foot and get what you want, that's what democracy is all about. And to take seriously the fact that the combination of democracy and capitalism can leave some people in the lurch, can leave some people not prospering, even though the GDP goes up, a lot of people are not participating in that wealth, that's a problem.

3:17:17.3 SC: And a good functioning, long-term healthy democracy will be good for everybody and that's a... Again, it doesn't happen automatically. You gotta work at it. I do think it's possible. I am optimistic about the prospects in the sense of, I do think it is possible to imagine functioning, flourishing democratic institutions in places like Europe and the United States and everywhere else in the world, that not only give people a vote, but give people economic opportunity and give people the rights that they should all have as human beings.

3:17:51.7 SC: And with that, slightly optimistic note, let's call it an end for this month, my voice is giving out, but thanks again for supporting the Mindscape Podcast. Hope next month won't be late, but you know, you never know, it's in the future. Very hard to make predictions about the future. Take care, bye-bye.