Every academic who attends conferences knows that the best parts are not the formal presentations, but the informal interactions in between. Roughly speaking, the perfect conference would consist of about 10% talks and 90% coffee breaks; an explanation for why the ratio is reversed for almost every real conference is left as an exercise for the reader.
Yesterday’s talks here in Avignon constituted a great overview of issues in cosmological structure formation. But my favorite part was the conversation at our table at the conference banquet, fueled by a pretty darn good Côtes du Rhône. After a long day of hardcore data-driven science, our attention wandered to deep issues about fundamental physics: is the entire history of the universe determined by the exact physical state at any one moment in time?
The answer, by the way, is “yes.” At least I think so. This certainly would be the case is classical Newtonian physics, and it’s also the case in the many-worlds interpretation of quantum mechanics, which is how we got onto the topic. In MWI, the entirety of dynamics is encapsulated in the Schrodinger equation, a first-order differential equation that uniquely determines the quantum state in the past and future from the state at the present time. If you believe that wave functions really collapse, determinism is obviously lost; prediction is necessarily probabilistic, and retrodiction is effectively impossible.
But there was a contingent of physicists at our table who were willing to believe in MWI, but nevertheless didn’t believe that the laws of microscopic quantum mechanics were sufficient to describe the evolution of the universe. They were taking an anti-reductionist line: complex systems like people and proteins and planets couldn’t be described simply by the Standard Model of particle physics applied to a large number of particles, but instead called for some sort of autonomous description appropriate at macroscopic scales.
No one denies that in practice we can never describe human beings as collections of electrons, protons, and neutrons obeying the Schrodinger equation. But many of us think that this is clearly an issue of practice vs. principle; the ability of our finite minds to collect the relevant data and solve the relevant equations shouldn’t be taken as evidence that the universe isn’t fully capable of doing so.
Yet, that is what they were arguing — that there was no useful sense in which something as complicated as a person could, even in principle, be described as a collection of elementary particles obeying the laws of microscopic physics. This is an extremely dramatic ontological claim, and I have almost no doubt whatsoever that it’s incorrect — but I have to admit that I can’t put my objections into a compact and persuasive form. I’m trying to rise above responding with a blank stare and “you can’t be serious.”
So, that’s a shortcoming on my part, and I need to clean up my act. Why shouldn’t we expect truly new laws of behavior at different scales? (Note: not just that we can’t derive the higher-level laws from the lower-level ones, but that the higher-level laws aren’t even necessarily consistent with the lower-level ones.) My best argument is simply that: (1) that’s an incredibly complicated and inelegant way to run a universe, and (2) there’s absolutely no evidence for it. (Either argument separately wouldn’t be that persuasive, but together they carry some weight.) Of course it’s difficult to describe people using Schrodinger’s equation, but that’s not evidence that our behavior is actually incompatible with a reductionist description. To believe otherwise you have to believe that somewhere along the progression from particles to atoms to molecules to proteins to cells to organisms, physical systems begin to violate the microscopic laws of physics. At what point is that supposed to happen? And what evidence is there supposed to be?
But I don’t think my incredulity will suffice to sway the opinion of anyone who is otherwise inclined, so I have to polish up the justification for my side of the argument. My banquet table was full of particle physicists and cosmologists — pretty much the most sympathetic audience for reductionism one can possibly imagine. If I can’t convince them, there’s not much hope for the rest of the world.
Most thinking hard core anti-reductionists wouldn’t say that macroscopic behavior cannot be derived from microscopic behavior, but instead that many details of microscopic behavior are IRRELEVANT to the long-distance long-time correlations. i.e. the long-distance correlations depend of organizing principles and aspects like symmetry and dimensionality. For instance, I can predict for you the low temperature functional form of the heat capacity of the a chunk of silicon, without knowing anything about the details of the crystal bonding. The only things that matter are the crystal structure and the speed of sound in the material.
Allen,
Thanks for your thoughts, but to be honest it was a bit above my level of understanding.
One thing to add:
“What quantum mechanics in fact yields are merely the probabilities…”
I’ve heard this many times, and it’s probably true. But I think it shows the limits of both our knowledge and technology, rather than any truth about the workings of sub-atomic particles. Sub-atomic particles cannot act probabistically in reality. Everything outcome must have a cause.
An analogy would be tossing a coin. We can look at the probabilities of the coin coming up heads or tails as being 50/50 for any toss. But looking at any individual toss we would be guessing the outcome unless we have more information, such as the starting position of the coin, the direction and placement of the force upon the coin, the landing position of the coin, its weight, local gravity etc. If we had such information, and knew its effects, we could say for certain what the outcome of the toss would be. Probabilities only appear when dealing with multiple events, and while the probabilities can be clearly established, they don’t tell us anything about ‘why’ they are the way they are.
As I said before, we may only ever be able to work with probabilities in quantum mechanics, but that doesn’t mean that’s all there is. There is no reason to believe every single event has not been determined from the beginning.
Sean,
it will be good exercise for you 🙂
Who knows if there are causeless causes (‘fundamental laws) or if, instead, reality acts more like John Wheeler’s participatory universe, where universe brings into being observers which bring into being universe which brings into being…in a never-ending self-reflexive loop.
Daniel (#49 & #52),
You should study up on Bell’s theorem, which essentially rules out the perspective you are proposing; at least as an interpretation of quantum mechanics.
To summarize the results: The logical implications of the view of reality you are taking imply a specific inequality for a particular quantum-correlation experiment. However, the straight-forward calculations of quantum mechanics violate that inequality.
Tests of this inequality that have been done, to date, support quantum mechanics. Some people do not think that the experimental tests so far have completely nailed down the coffin lid on disproof of the inequality; but no one claims that QM can be consistent with it.
@47 Pete – I think the results of the paper should not be dismissed so easily, and are worthy of consideration in the discussion. The fact that, with full knowledge of the microscopic description of the system, one cannot compute certain macroscopic observables in the model would certainly suggest that knowledge of the microscopic laws is not enough – is that not contrary to the point of reductionism? Do we have different working definitions of reductionism in mind? I am under the impression that reductionism suggests that, in principle, if we know all the microscopic laws and initial state of the system we can compute any macroscopic observable at a later point in time. The paper seems to suggest that this is not the case, at least in the system considered. It may be true that the values of macroscopic observables we can observe are constrained by the microscopic laws (e.g., due to symmetries of the interactions, the ranges of interactions), but if we can’t in principle compute exactly these observables then I wouldn’t consider reductionism to have done its job.
As for the fact that this is an infinite system, although our real physical universe is perhaps finite and discrete at a certain microscopic scale, our models of the universe typically are not. We typically assume an infinite volume universe or a continuum limit for our models, and the results of the paper may apply to such models. This would force us to get around this issue by building finite-volume, discrete models, but we must then assume that, like phase transitions, the result described in the paper only works for infinite or continuum systems. Perhaps we can in principle do this. So, maybe your objection stands. However, maybe someone can make a non-computability argument in a finite system, and then the infinite system limit isn’t a problem for the paper’s argument. I don’t know if the latter is impossible or not.
Now, these are not arguments to claim that reductionism is necessarily false, only that serious consideration to the possibility that relying on only computing things from knowledge of the microscopic laws and initial conditions is not enough to provide a complete description of the macroscopic universe.
It seems people are confusing reductionism with scale. That is, macroscopic=f(microscopic) is only a specific kind of reduction, and is also not universal. Something macroscopic can indeed be fundamental. The simplest example that comes to mind is a structure made of building blocks. It’s shape is completely independent from the properties of the block.
@ 54 Neal,
Regarding Bell’s theorem see: Patrick Hayden & David Deutsch
http://arxiv.org/abs/quant-ph/9906007
“All information in quantum systems is, notwithstanding Bell’s theorem, localised. Measuring or otherwise interacting with a quantum system S has no effect on distant systems from which S is dynamically isolated, even if they are entangled with S. Using the Heisenberg picture to analyse quantum information processing makes this locality explicit, and reveals that under some circumstances (in particular, in Einstein-Podolski-Rosen experiments and in quantum teleportation) quantum information is transmitted through ‘classical’ (i.e. decoherent) information channels.”
If my understanding is correct, Bell’s theorem assumes a single outcome. Under the MWI interpretation each outcome occurs. That makes all the difference.
But can reductionism explain this story from NPR?
http://www.npr.org/2011/04/22/135121360/a-boy-an-injury-a-recovery-a-miracle
@ 58 Phil,
Well, the boy says that “I was driving for a lay-in and then I got pushed from behind the back, and I hit my lip on the base of the basketball hoop.”
Unless he means the stand or the pole holding up the basketball backboard and hoop, the first miracle was someone that short jumping that high.
Perhaps. But that’s not the point of the story. Read the whole thing.
@ 60 Phil,
OK, I read the whole thing. What’s the point? God of the gaps? NPR’s reporting? The Church’s trial? I agree with the guy who said it’s a “joke” — though of course not for the family. Sorry, I’m not sure what point you’re trying to make here.
@ 61, See my comment #58 for the point I’m trying to make.
@ 62 Phil,
Your point is a question? Can reductionism provide an explanation?
If you mean can reductionism explain the boy’s recovery, then the answer is most certainly yes. Just because our understanding of the physical world doesn’t as yet provide an adequate answer (I’m assuming this, maybe it does even today, with enough investigation and piecing together of the admitted medical puzzle), that doesn’t mean answering it is impossible other than through positing a deity. In fact, I would suspect this type of “miracle” is ultimately more amendable to an easy explanation in the reductionist sense than many of the difficult issues raised on this particular thread.
If you mean did the boy recover as the result of a miracle, then the answer is no. That is a perfect example of a bad explanation since it can be used to explain anything: why he recovered, why he died, why he’s still in a coma and the like: God did it.
If you mean do some people believe the boy recovered as a result of miracle, then the answer is yes. People have a multitude of bad explanations for what happens around them. Over time those explanations have gotten progressively better, and (with some luck) they will continue to improve.
“If you mean did the boy recover as the result of a miracle, then the answer is no.”
How do you know this?
How do I know that an ET didn’t do it? How do I know you didn’t do it? You’re taking the view of a “God of the gaps”: say something is uncertain and then attribute it to God. Over history that explanation has been used to support all manner of incorrect ideas. We didn’t know the nature of the Sun — so it must be a Sun God and on and on. These are simply bad, dead-end, explanations because they can be used to support any theory anybody wants to posit, and they don’t lead to progress in discovery real answers. What would convince you? If tomorrow a doctor emerged who presented a well-documented, solid, scientific account of what caused the boy to recover, would you then change your fundamental view? Or, would you just point to other things of which we are uncertain and attribute them to God? I suspect the later.
How do you know God doesn’t exist? Reductionism?
No, not reductionism alone, though as I said, over time this approach has led to more and more areas that were once the province of myth, spirits and God coming under the domain of science. However, what’s even more important is, as I have tried to explain, the nature of good and bad explanations.
So you know God doesn’t exist because of reductionism and something else? What the something else? I thought reductionism is all you need to explain anything.
I said, several times, what the “something else” is. In addition to a reductionist stance, you need a good grasp of good and bad explanations. Not those that can serve equally any crackpot assertions, like Ram, the God of the Sun, caused morning to rise each day upon the world (or allowed this remarkably good jumper to recover). You know you’re not resonding to anything I’ve said. Why is that? Anyway, I think everyone, including Sean, would like to see this particular discussion come to a close. Have a nice Easter my friend.
When arguing with fellow physicists about this, the best strategy is to invoke Uri Geller. Everyone will then agree that limits on new forces based on fundamental physics can be used to rule out paranormal effects (this was discussed on this blog some time ago). If one wants to allow for some room for people to not be strictly described by the fundamental laws of physics, then that room cannot exist at the single particle level, anomalous behavior is assumed to exist in the correlation functions of vast numbers of particles.
Now people are especially motivated to propose such exceptions to the laws of physics because they don’t believe that when they think of something, the thought processes strictly follow the laws of physics. Then this leads quite naturally to loopholes allowing someone to read your mind, because we now cannot rule out that the collective behavior of large number of particles in someone’s brain can be influenced by what is happening in your brain, even though at the single particle level, no strange new forces are acting. It is just that there exist new, as of yet unknown laws, for the way some large numbers of particles interact and these will manifest themselves precisely in mental thought processes. 🙂
@ 69, If a doctor came up with a natural explanation, and had evidence to back it up, that explained the boy’s recovery, then I will disbelieve the miracle explanation. Until that happens, I’ll keep my mind open, and so should you.
Happy Easter to you too.
I know this was a passing remark incidental to the point of this post, but I wanted to say students can benefit from the current structure. Undergrads, grad students, beginning postdocs – these people, unlike established faculty (like Sean), don’t have a bazillion people they know at the conference. They’re not going to be included in any of these productive side conversations. They’re going to be hanging out with anyone from their institution (if the conference is big enough that there are some others there). The talks are a place for them to hear other ideas.
And sure, maybe they should be out networking. But the established people already have a full schedule talking with people they already know. So as nice as they may be, they’re not going to be looking for chatting up young students they don’t know (unless the student is really extraordinary, and has made a splash with some major publications).
Not so open your brains fall out, I hope. Really, this “open mind” business is a really boring theme from people who use it simply to mean “I have no evidence or coherent theory to back up what I’m saying, but I would like to deflect any criticism you might make by accusing you of narrow thinking”.
*sigh*
Well, you might say that I DO have evidence, namely, the lack of any evidence of natural causes for this boy’s recovery. They prayed, and then the boy was healed, completely stumping the doctors. The explanation being a miracle sounds more credible, at this point in time, than an explanation from natural causes. Of course, if evidence is found of natural causes for his recovery, I will tend towards THAT explanation. Until then, I will tend towards the explanation that he was healed by a miracle. You want some sort of sign that God exists, well there you have it. What more do you people want? There’s more to reality than reductionism, but if you keep on with your “narrow thinking”, you’ll never see those instances of there being anything outside of the natural.
Phil (#74):
Like the Bible says with fruits, scientists use the fruits that they have, instead of inventing new fruits. They compare what they experience with the fruits that they already have to figure things out.
So one can look at that recovery and come up with hypotheses and if someone wants to call that ‘G_d’, then more power to them, but that isn’t an explanation, especially since the word itself can be used to mean anything.
So scientists limit themselves. And try to be very specific in that “in this experiment, at this time, at this location, under these conditions, we found such and such to apparently be the case…”
And yes, they are subject to tribalisms, anything human is. Hopefully, they will follow the evidence wherever it leads, no matter how uncomfortable it makes them.
People have to love to learn to live with being limited…or go crazy denying it 🙂