It remains embarrassing that physicists haven’t settled on the best way of formulating quantum mechanics (or some improved successor to it). I’m partial to Many-Worlds, but there are other smart people out there who go in for alternative formulations: hidden variables, dynamical collapse, epistemic interpretations, or something else. And let no one say that I won’t let alternative voices be heard! (Unless you want to talk about propellantless space drives, which are just crap.)
So let me point you to this guest post by Anton Garrett that Peter Coles just posted at his blog:
It’s quite a nice explanation of how the state of play looks to someone who is sympathetic to a hidden-variables view. (Fans of Bell’s Theorem should remember that what Bell did was to show that such variables must be nonlocal, not that they are totally ruled out.)
As a dialogue, it shares a feature that has been common to that format since the days of Plato: there are two characters, and the character that sympathizes with the author is the one who gets all the good lines. In this case the interlocutors are a modern physicist Neo, and a smart recently-resurrected nineteenth-century physicist Nino. Trained in the miraculous successes of the Newtonian paradigm, Nino is very disappointed that physicists of the present era are so willing to simply accept a theory that can’t do better than predicting probabilistic outcomes for experiments. More in sorrow than in anger, he urges us to do better!
My own takeaway from this is that it’s not a good idea to take advice from nineteenth-century physicists. Of course we should try to do better, since we should alway try that. But we should also feel free to abandon features of our best previous theories when new data and ideas come along.
A nice feature of the dialogue between Nino and Neo is the way in which it illuminates the fact that much of one’s attitude toward formulations of quantum mechanics is driven by which basic assumptions about the world we are most happy to abandon, and which we prefer to cling to at any cost. That’s true for any of us — such is the case when there is legitimate ambiguity about the best way to move forward in science. It’s a feature, not a bug. The hope is that eventually we will be driven, by better data and theories, toward a common conclusion.
What I like about Many-Worlds is that it is perfectly realistic, deterministic, and ontologically minimal, and of course it fits the data perfectly. Equally importantly, it is a robust and flexible framework: you give me your favorite Hamiltonian, and we instantly know what the many-worlds formulation of the theory looks like. You don’t have to think anew and invent new variables for each physical situation, whether it’s a harmonic oscillator or quantum gravity.
Of course, one gives something up: in Many-Worlds, while the underlying theory is deterministic, the experiences of individual observers are not predictable. (In that sense, I would say, it’s a nice compromise between our preferences and our experience.) It’s neither manifestly local nor Lorentz-invariant; those properties should emerge in appropriate situations, as often happens in physics. Of course there are all those worlds, but that doesn’t bother me in the slightest. For Many-Worlds, it’s the technical problems that bother me, not the philosophical ones — deriving classicality, recovering the Born Rule, and so on. One tends to think that technical problems can be solved by hard work, while metaphysical ones might prove intractable, which is why I come down the way I do on this particular question.
But the hidden-variables possibility is still definitely alive and well. And the general program of “trying to invent a better theory than quantum mechanics which would make all these distasteful philosophical implications go away” is certainly a worthwhile one. If anyone wants to suggest their favorite defenses of epistemic or dynamical-collapse approaches, feel free to leave them in comments.
I entirely agree that consciousness has nothing to do with it and my essay, kindly linked to and reviewed by Sean, takes brief aim at that view. A long time ago I wrote an article called “Pathological industries of the quantum” which sought to shaft the quantum consciousness viewpoint in more detail but I never tried to publish it. I think that there is nothing more to it than “Here’s something we don’t understand; here’s something else we don’t understand; hopefully there’s a connection between them.”
Sean:
No indeed, I may not demand a unique answer to that question, but if I assume that there isn’t one then I’ll never find it if I’m actually wrong and there is one; whereas if I assume that there is one then I stand a chance of finding it…
Re the transition from quantum to classical I go with Nico van Kampen’s view, which I think cleans it up. I try to explain that too in my essay to which Sean links above, although in a fairly compressed way. I corresponded with van Kampen (who died two years ago at a grand age and wrote a book on my earlier field of plasma physics) and I thanked him for his explanation, but we then each accused the other of mysticism regarding Copenhagen (him) vs hidden variables (me).
On the subject of the origin of |psi|^2 as probability, I think this was cleared up by Steve Gull and Yoel Tikochinsky in J Phys A vol.33 p5615ff (2000); from memory this approach has been taken further by Philip Goyal.
Sean, if by “dynamical collapse” you mean dynamical models as in: “arxiv.org/pdf/1107.2138.pdf”, then I go for it.
Many-Worlds is a nonsense, I tryed to understand them but … it was an impossible mission, as they explain nothing from nothing.
On the other hand, dynamical models are capable of solving the quantum measurement problem and many other issues related to QM superposition principle. But be careful, Sean, if you focus too much in the collapse you are going to get lost. The complementarity principle here has to do with the paths visivility vs. interference patterns; thus, no room for collapses nor (perfectly mathematical) unitary evolution.
Take a look at Kocken-Specker for another nail in the coffin for HV.
Dear Bill James
I deal with Kochen-Specker (KS) in my essay linked to by Sean; please look at it. All that KS does is show that the hidden variables are at a deeper ontological level than the variables of quantum theory. Hardly surprising given that they have to be nonlocal and acausal.
Anton: “The predictions of QM violate causality in some situations and have been verified experimentally.” – could you please provide examples of this? I’d be interested to know what you mean exactly by a cause and an effect.
For example, I don’t think many physicists would consider the EPR experiment to be acausal because it doesn’t involve any kind of transfer of information between the measurement events. If something I do can’t, even in principle, transfer information to a thing that happens, then I don’t know how I could say I caused that thing.
If you picture each particle as a separate object with certain properties, and insist that those properties are physically real aspects of each object, then I would agree that you’re stuck with seeing EPR as acausal. That would seem to me to be a metaphysical choice, and metaphysical choices shouldn’t be the basis for a claim about a theory that doesn’t require them.
Bob,
I thought I’d done that explicitly in my essay, with the Bell analysis and the statement that the order of observation is not Lorentz-invariant. Also the Wheeler delayed-choice scenario. And the experimental verifications of these scenarios in the references. If these aren’t clear then please do say more.
The opposition to probabilistic predictions has long confused me. It’s not possible to produce a prediction in Newtonian physics of a real experiment that is not probabilistic either, for the simple reason that there’s always some uncertainty in the inputs. For most experiments, uncertainty in the experimental apparatus is far larger than the quantum uncertainty anyway. That quantum mechanics places a lower limit on the uncertainty we can possibly achieve is, for nearly all applications, an irrelevant detail.
It feels like people that object to quantum uncertainty (or the number of worlds in the Many Worlds interpretation) do so because the philosophical implications make them uncomfortable. I have no patience for that kind of thinking any longer. Nobody’s discomfort changes reality: it’s just an emotional mask that hides the more objective methods of induction (e.g. counting the number of assumptions or free parameters).
Hi Anton, yes, I read your essay. It’s very interesting. It doesn’t address the question I asked, as far as I can tell; that’s why I asked.
I’m claiming that one would only interpret the results of those experiments as violating causality if one adopts particular metaphysical assumptions that are not a part of and not required by the theory. To me, that suggests it’s those assumptions that violate causality, not the experiments and not the theory.
Imagine the most absurd universe you can think of. There exists googles upon googles of universes just like that, except that the stars in the sky are arranged to look like an image of the cover of Sean Carroll’s latest book, but with my name as the author, with one word misspelled. And there are still googles of universes like that. Many more than the ones that host a Boltzmann Brain.
Thats my problem with the MWI.
But much, much worse, like when I try to justify eating a hamburger to my vegetarian nephew, is that I realize in the debate against the MWI theory, logically, I have the weaker position.
Sigh.
@Joseph Marino: [[Since you are on the subject of alternate interpretations of QM, Dr. Carroll, I’ve been interested in learning more about Two-State Vector Formalism for a while, now, as I find the idea of retrocausality to be extremely interesting; unfortunately, I’ve had a great deal of difficulty finding any information on TSVF geared toward laypersons.]]
Instead of focusing specifically on TSVF, I would explore time-symmetric (‘retrocausal’) interpretations of QM in general. Two key proponents are Huw Price and Ken Wharton.
Huw Price: http://arxiv.org/find/quant-ph/1/au:+Price_H/0/1/0/all/0/1
Ken Wharton: http://arxiv.org/find/quant-ph/1/au:+Wharton_K/0/1/0/all/0/1
A good layperson-friendly overview: http://arxiv.org/abs/1307.7744
See also this recent online conference: http://www.ijqf.org/forums/forum/quantum-foundations-workshop-2015/retrocausality-and-transactions
Advantages of the time-symmetric approach:
1) it’s the only realist psi-epistemic interpretation
2) all entities live in spacetime (no weird ‘configuration space’ ontology is necessary)
3) EPR-Bell scenarios are explained without invoking nonlocality
4) Retrocausality is already implied by CPT symmetry in combination with the quantized nature of light (see Price/Wharton paper)
IMO, it’s the best alternative to the Everettian approach currently on the market. 🙂
Jason: probabilistic prediction is fine provided you regard it as provisional, but isn’t it the job of scientists to improve testable prediction? That means tighter probability distributions, with delta-functions as asymptote.
@phylophysique: Thank you very, very much! That is incredibly helpful!
Early on in the process of writing simple computer programs for games (as a hobby), I learned that adding randomness (or pseudo-randomness) to a game-world is often essential. For one reason, in a completely deterministic game-world, there may be traps which the game can fall into and never be able to get out of (except by the player rebooting the game). Adding a small random element gives a way out of these traps (after hundreds of tries which take milliseconds of real time). Also, a game which is too predictable is not fun for long.
Anyway, I think a universe with a small random element is the best kind, and I personally would not want to live in one without that element (but it should be small, so we can learn how to make approximate deterministic predictions which are useful).
My approach to understanding (and discussing) Physics is to first focus on the “great experiments”: What was done and what was shown. This includes not only physical experiments, but also the great gedanken-experiments. Then, to the limit of my modest mathematical knowledge, I try to explore and comprehend the relevant theory. I am awed by the amazing web of physics theory, where the brightest nodes are the great experiments.
I was gobsmacked to realize that, prior to reading the linked post, I had not heard of the “insanely great” Stern-Gerlach apparatus, clearly a massive gap in my awareness and education. (Or, possibly, evidence of forgetfulness. But let’s not go there.)
I would greatly appreciate future pointers to discussions that link key concepts and the associated key experiments (drill down through the turtles), especially in the context of current thinking, and where the “line” presently rests between what in current physics is known experimentally and what is not.
Got me some edjumakashun today. Thanks! And I’m wondering if there’s a Stern-Gerlach apparatus operating nearby… This, I gotta see.
Theoretical physics is hard. It was hard for me at first, reading about it in books for laymen. It was really difficult to absorb with a cold eye of scrutiny. Most of us are now raised to be good little scientist, and we are supposed to adhere to concepts of logic and reason. I feel like a lot of theoretical physicist get a bad wrap, because it is just so damn weird people don’t know what to believe. Then I believe strongly in the validity of most of all the concepts in the Standard Model, despite it’s quantum weirdness.
Here is my secret. Most books about theoretical physics explain Special Relativity at the start. Then when it got to topics about quantum mechanics, I would put down the book and ask myself how that could be Lorentz co-variant. If you assume that quantum weirdness is an emergent property of Lorentz co-variance that is the hidden variable acting as a mechanism behind the quantum weirdness, it makes a lot more sense.
Then pieces of the puzzle can start falling into place. Then through abductive reasoning, you can find that it is a very strong possibility. It would all just fit in too well to be just a coincidence. It would even make the hidden variables be non-local.
The only problem with this is that it doesn’t seem to work out mathematically, and you have to be a crank in order to understand quantum mechanics. Either that is true, or I have completely lost my mind from reading too many books about theoretical physics. Well, I did just say I understood quantum mechanics…
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@JasonDick You said:
“The opposition to probabilistic predictions has long confused me…It’s not possible to produce a prediction in Newtonian physics of a real experiment that is not probabilistic either, for the simple reason that there’s always some uncertainty in the inputs…It feels like people that object to quantum uncertainty (or the number of worlds in the Many Worlds interpretation) do so because the philosophical implications make them uncomfortable. I have no patience for that kind of thinking any longer. Nobody’s discomfort changes reality: it’s just an emotional mask that hides the more objective methods of induction (e.g. counting the number of assumptions or free parameters).”
1) Please don’t confuse something epistemic (our inputs can never be infinitely accurate), with whether or not the system is ontologically deterministic itself.
2) I have no patience for individuals that blindly assume “Well hey, of course the universe is indeterministic!! QM says so!” No it doesn’t, and the fact that you would endorse something so close to magic is beyond me. What generates this indeterminism? So something just comes from nothing and affects the system? Are you kidding me?
@Ken K: All of the “googles of universes” would still have to obey certain universal (“multiversal”) laws of physics. One example, either:
1. Regardless of the imaginings of many television writers, it must be impossible to cross between universes. If it were possible, then the Fermi Paradox would apply.
2. MWI is wrong. (I suspect this to be the correct answer.)
Hi Anton. You said:
“I entirely agree that consciousness has nothing to do with it and my essay, kindly linked to and reviewed by Sean, takes brief aim at that view.”
I myself did make a very negative review against the book “The Quantum Enigma.”
http://www.amazon.com/review/RH8W198ZKZFVU/ref=cm_cr_rdp_perm
My knowledge of physics is layman and humble. I am highly interested in the consciousness issue. And try as I might, I cannot see good connections between consciousness and Quantum Mechanics; I could not find any in the book afore mentioned.
You also said:
“I think that there is nothing more to it than “Here’s something we don’t understand; here’s something else we don’t understand; hopefully there’s a connection between them.””
Sean Carroll said pretty much the same thing in a debate on the issue of life after death, if my memory serves me well. The debate is in the url below:
https://www.youtube.com/watch?v=lzCYva2aYCo&index=62&list=LL-WSR1zfcO5C7nzhBKExfAw
I must say that the debate itself, IMNSHO, was very bad and misinformative. And this is true for all the four debaters. I cannot understand why people agree to debate things they know so little about… (Moody lives in his own private shelf regarding this subject. Alexander is mesmerized by his own NDE, without truly having come to grips with it, although already profiting from it… Novella did not say anything enlightening that I can remember. And Sean, well; he is a good physicist…).
But Sean did say something pretty much similar to that phrase of yours above. Even though I think that there is a huge probability (and I mean Huge Indeed!) that there is no connection between QM and the Consciousness issue, I do not think this mystery-mystery assertion does justice to the question. In fact, I think it is misinformative and counterproductive. Also, it is unduly derogatory against all those who try to find a connection between these two issues. Different people see connections between QM and Consciousness due to a plethora of different reasons. Some do embark on the mystery-mystery bandwagon. Some, like the authors of “The Quantum Enigma,” try to follow a more descriptive step-by-step rationale, which I think traces down to a von Neumann-Wigner interpretation of QM that actually tries to pin down the causation chain of the whole issue. Some see qualitative similarities between, on the one hand, the picture of reality that QM seems to show us and, on the other hand, basic features of the conscious experience (I think philosopher David Chalmers and also physicist Roger Penrose have arguments along these lines).
One thing that I myself find particularly intriguing (even though I do think it is most likely utterly inconsequential) is the fact that, on the one hand, the only causeless phenomena that “Science knows of” are some quantum events, and the fact that, on the other hand, the only effectless phenomena that “Philosophy knows of” is consciousness. It is indeed tempting to tie the two and make some sort of Ouroborus Universe…
https://en.wikipedia.org/wiki/Ouroboros
That would make a very elegant Universe indeed, where not only quantities are conserved (mass/energy, etc) but also the causation chain itself would be… “conserved” (i.e. self contained). Elegant as it might seem (or, some may say, aberrant…), as the state of the art is it fits more fiction than fact.
Sean, do you have a favored (non-pragmatic) argument for favoring ontological simplicity (of some sort) in our theorizing about the world?
I think the justification is ultimately pretty pragmatic. If you have two theories with equal empirical success, the ontologically simpler one gives you more understanding for less input.
I am sure I have a naive understanding of it, but I cannot get my head around how a double slit experiment can generate another world. I believe we must assume that the World’s we do not observe must for sake of argument contain approximately the same amount of matter and energy as the one we persist in. I just find it an incredulous burden on the poor electron to birth a universe for sake of Occam’s razor.
Hi Anton,
It’s nice to talk to you. I’m sorry for the delay, I wrote that and almost immediately went to sleep and got busy the next few days.
I don’t think it’s finished at Quantum Mechanics, but that there will likely be additional tiers of physics. We have a long way to go and will of course spend a lot of time trying to figure out the consequences, but there must ultimately be something to drive QM to behave the way it does which doesn’t really fit QM or Classical. I wouldn’t at all suggest string theory, if only to annoy Greene and Suskind, but it’s a damn fine candidate so far; ignoring that it’s the ONLY candidate exploring such insane mathematical descriptions this far. It’s somewhat valiant because the more productive thing to do is fully realize QM before moving. Of course String Theory is an attempt at unification, but I think it will uptimately fail at that but pleasantly present an underlying truth which noone was really looking for.
Just as we found that classical mechanics really shares physics with quantum mechanics, I think we’ll find something beyond both of these and come to the realization that physics can be divided into three primary branches. Complete speculation, but my speculation has a certain charm to it 🙂