Quantum Interpretation Poll (2011)

malreux

Although one can debate the categories you offer as options, I think this poll is a great thing and should def become an official annual event for phys forum. People offer similar things at foundational conferences.

However, like everybody else, I imagine my own 'interpretation' of QM doesn't quite square with any of the options - I'd even prefer a vaguer description as an option, like 'quantum theory is a theory of local interactions and nonlocal states' to sum up my stance. Regardless, good work on starting this thread! It's cool to have a handle on what people are thinking.

lmoh

I've always wondered what the difference is between Many Worlds ( With splitting of worlds ) and Everettian MWI (Decoherence). What is the difference between splitting and decoherence such that 13 people would flock to the former and 17 to the latter?

malreux

Good question! I settled for the latter, but the distinction is vague, as stated. Does it mean that e.g. Lev Vaidman would plump for the former and e.g. Hilary Greaves would plump for the latter?

Personally, I think the only important distinction between MWI proponents is between those who thought 'worlds' had to be added to the formalism (to derive 'many exact worlds') and those who appeal to decoherence and the Church of the Larger Hilbert Space. [Note tenses]

Ken G

An example might help-- in what theory is a spot on a screen not an observable?
Yes, I take your meaning-- naive realism is not tenable, but structural realism is a kind of compromise. The best of both worlds, or all the problems of each without any solutions? Murky waters, to be sure, it contents me to say that we impose our way of interacting with nature when we try to describe nature, so we are involved in deciding what we shall regard as real.
I still don't think it's that hard to distinguish the claim "large reptiles roamed the Earth and left footprints and fossils", which is a theory (it unifies a bunch of observations and makes testable predictions) from the claim "the electron definitely goes through one slit, decided by hidden aspects of its preparation, but the hidden aspects evolve dynamically as an unobservable pilot wave that goes through both slits", which is an interpretation of the Schroedinger equation (and adds nothing to the observations that we can use the Schroedinger equation to predict). I think the problem is, you are talking about how we interpret observations, but how we interpret observations is what a theory is because it involves being able to predict those observations. I am talking about how we interpret our theories, not our observations, so it does all begin with a distinction between what we observe and how we understand and predict what we observe. Your point that such a distinction can be problematic is well taken, but that doesn't mean it is invalid to see value in the distinction, the distinction is just not as clear as we might like.
Presumably he was checking the novel predictions, the other half of good science.
I doubt anyone holds that this is the "sole" or "main" duty of a scientific theory, only that it is a required duty.Yes, but that is not all they do, to be a theory. All good scientific theories have made predictions about things that hadn't been observed yet. If all a theory does is tie together existing data, no matter how tidily, it is not a scientific theory, it is just a nice piece of rationalization. It certainly hasn't happened yet that a good theory has been like that, but we are just starting to see some theories like that now (string theory, chaotic inflation, etc.), and there are serious questions around whether these are science or rationalization.
Well I'm not sure exactly what Wittgenstein said, though I'd be interested in hearing it But I'm not sure I'm going to think he was right, because the geocentric vs. heliocentric controversy was a classic example of two different theories being decided by the different predictions they made (most notably around telescopic observations of the phases of Venus, and elliptical orbits). Prior to the observations (by Galileo and Tycho), no person on Earth had any idea which was going to be the better theory, they could only guess.
Well, I'm not sure what is the most interesting aspect of the equivalence, my point is only that they are equivalent, yet invoke such completely different ontologies that it becomes clear we are not answering "what must the world be like for this theory to work well."

malreux

[1] There's a type of structural realism - to which I do not subscribe - called epistemic structural realism. Some proponents of which take it that even looking at blood cells under a microscope is somehow 'theory-laden'. Whatever you think of that view (I think its crazy), you correctly infer my real meaning in [2].

[2] Yup. Laws describe / explain /predict some classes of observations, not others. Fields make sense with cut-off's, not otherwise (despite the project of algebraic-approach axiomatic field theories best attempts, etc.)

[3] Well, this is a bad interpretation, so far is goes, because in this case the hidden variables are 'idle wheels'.

[4] I'm gesturing, with only a little argument, to the status of observable/non-observable. For the logical empiricists of the early twentieth century, this distinction was paramount, despite the fact the QM revolution had already showed this distinction to be, as you put it, 'problematic'. However, I previously began with the crackpot* tactic of comparing my view to Einstein's - I stand by my paraphrase - observables are defined within some theory. This needn't drive one to the extremes of ESR, nor make one particularly interested in contextual epistemology and so on. As distasteful as I ultimately find their antirealism, it's worth checking out http://plato.stanford.edu/entries/co...ve-empiricism/ if your interested in how this distinction plays out for modern empiricists.

[5] I'm not sure if this is entirely historical accurate; regardless, the crucial point your making is that at various junctures in the history of science, a 'crucial experiment' has often been the ultimate arbiter between competing theories.

[6] Unfortunately, your going to be very disappointed about the future of physical research. One thing that's happening here I think is we're gradually coming out of one paradigm and entering another, in terms of e.g. experience and fundamental physical research. A lot of things that the early originators of QM thought were impossible to talk about, or were inherently arbitrary, are now routinely examined in the lab, or by the theorist. I'm thinking here of the quiet revolution re POVM's, and also the viability of the modern medium decoherence programme. On the other hand, we're rapidly approaching regimes where no viable experimentation will be likely to occur - the most obvious case: quantum gravity. Further, some of the 'problems' of interpretation just aren't physical problems - e.g. if we have a viable interpretation of the formalism of QM that is capable of being rendered relativistically covariant - I'm thinking here of MWI - and also provides a 'realist' interpretation of the theory, i.e. like all previous scientific theories, then it really seems to me that the outstanding questions about such an 'interpretation' are purely philosophical. They arise because some intuitions - e.g. 'experiments have unique outcomes' - are difficult to work around or without. Hence a place where a philosopher might actually have something useful to say. (Or not ;-))

[7] My interpretation of what he meant is: one class of observations that were useless to Galilei's contemporaries are observations of the sun itself - since it might look the same whichever theory is correct. Point being that the theory predicts other observations to test. An example from Deustch might clarify: why was the ancient Greek theory about the seasons a bad explanation? They thought (roughly) that the cooler seasons arose from Persephone being snatched by the lord of the underworld, and the warmer season from Persephone being returned to her divine mother, in a cyclical process. However, if they had travelled further south, they would have noticed a class of observations difficult to reconcile with this view. I.e. opposite seasons. The complications to the narrative would have been mighty, of course, but the myth has no resources to accept these new observations. The theory whereby the Earth spins on an axis tilted with respect to its own planar rotation can not only accommodate these observations, it predicts them. Notice how the predictions re observations arise from the theory - the theory is realist, but it doesn't matter (scientifically) that the theory is realist in the sense of entity realism i.e. asserting the reality of entities 'Earth' and so forth. Indeed, since SR suggest a rigid body cannot be defined (is not physically possible), fundamentally, the Earth cannot be a rigid ball with titled axis. At a certain level of description, however, this is a perfectly fine thing to work with.

[8] Yes, exactly right.

[9] Please note I didn't want to talk about "what must the world be like for this theory to work well" but "what must the world be like if our (best) theories are approximately true. Regardless, look there's a lot I could say here but we've been dragging this conversation on further and further away from the subject of this thread. If the mods don't mind, then let's carry on, otherwise we should start a new thread.

Your [9] needs to clarify some things - what exactly is the 'ontology' of the Hamiltonian, for example? This is not as easy a question as it (may!) seem. Sometimes we're discussing the status of things like ordinary tables and chairs with regards to fundamental physical ontology (emergence?), other times we're discussing the ontology of particular physical theories (is the wavefunction real?). We could focus this discussion a lot more on a new thread if you think its worth it.

A note on structural realism as the worst of both worlds: I tend to think of it (unsurprisingly!) as the best of both of worlds, conversely. This works by combining two arguments - the (1) 'no miracles argument' and (2) the 'pessimistic meta-induction' (sounds grandiose, right?). (1) states that it would basically be a miracle if our scientific theories weren't even remotely true, because we predict phenomena, safely use technology (sometimes!), etc. So, to some extent, our best theories approximate the truth (a fortiori). (2) is usually presented as an induction, though it also has a deductive variant (that isn't sound, so ignore it): scientists had good reason to believe past scientific theories (evidence, predictions), those theories have all turned out to be false, scientists have good reason to believe current theories, they will overwhelmingly likely turn out to be false, so we shouldn't believe our best theories. Whatever you think about this argument, it is clearly aimed at that I called 'entity realism' above - where you claim a class of entities predicted by some theory really exist. E.g. if, for example, an old theory of combustion predicted a substance called phlogiston, and a new theory jettisoned it from our ontology, replacing it with, say, oxygen, or rejecting what it doesn't 'replace' by stating there is no further use for such things, then the old entities are 'falsified' (in this sense). However, look at the continuities between the two theories of combustion - though one class of entities is out and a new class in, the actual structure of the mathematical description is not so sharply different. Consider the revolution of special and general relativity - they both contain Newtonian physics as a limit case. What is revolutionary and what is continuous are both structural features, mathematical cores. So perhaps these are the bits of our theories that, to some extent, latch onto nature. Or so I contend.
*In Baez's sense

Ken G

That has always been my objection as well, but I would stop short of calling it "bad", because it is very hard to use absolute terms when dealing with interpretations. Some very bright people, including de Broglie himself, thought it as a good interpretation, and for many of the same reasons that we think it is bad. So it is clear we don't agree on the requirements for a good interpretation-- that's an important thing to recognize about interpretations, perhaps even the most important thing. Even though I prefer some to others, and can give reasons why, I recognize them all as valid in their own way, and I'm glad to know them-- there's not one I wish I hadn't met!
I haven't penetrated to the controversy yet, because at first glance, constructive empiricism appears to make the claim from this quote:

"Science aims to give us theories which are empirically adequate; and acceptance of a theory involves as belief only that it is empirically adequate."

Naive realism, on the other hand, appears to make the claim from this quote:

"Science aims to give us, in its theories, a literally true story of what the world is like; and acceptance of a scientific theory involves the belief that it is true."

Now, looking at those two statements, it seems to me that the first is scientifically demonstrable as basically correct (basic scientific history suffices), though it unnecessarily and inaccurately stresses the word "only" (the clear fact is that this is one of science's most closely held goals, but it is not the only goal of science, the other involving a sense of unification and understanding that goes quite a bit beyond empirical adequacy). But all that is obvious. The second quote, on the other hand, is clearly naive and rather absurd, and again even a rudimentary knowledge of scientific history suffices to demonstrate that. I can't even imagine how anyone holding that opinion is going to even begin to define the phrase "literally true" in a way that is remotely scientific, without ending up sounding like the first statement.
Yes, the role of "crucial experiments" cannot be understated, they are what volcanoes are to island chains and what wars are to nations. The main theories of physics do not tiptoe in the back door, they erupt with great pomp and circumstance, and always with some experimental result that no one had any reason to expect in the absence of the theory. Usually the result precedes the theory, but the successful theory also predicts additional things we would have no reason to expect without the theory, and that's how we verify the theory is not pure rationalization of something already known.
Yes, POVM's are an interesting new direction to call attention to, and I can't see why I would have any "disappointment" associated with this. The intent of the program is, as usual in science, to be able to predict experiments, here those involving decoherence, such that the state of the system can be continuously tracked, not as an evolution from a pure state to a mixed state (which regular quantum mechanics does in concert with the Born rule or standard decoherence), but as evolution from a mixed state to a pure state. That's what is missing from quantum mechanics, and predictions along that path would be a new theory that would arrive with great fanfare and experimental confirmation.But do you think that is something new? The history of physics is peppered with periods where we were far from viable experimentation-- and it invariably led to a period of stagnation in physics.

As to the current state of affairs, we can certainly be optimistic if we are predisposed to be, but there is a danger that optimism gives way to self-deception and rationalization. The simple truth is, we have no reason to expect quantum gravity to provide us with a great new theory of physics that does not simply either repackage what we already know, or make predictions that we have no way of knowing would hold true if we could test them. Regardless of how aesthetically pleasing we might find notions of quantum gravity, that is just a sorry state of affairs, for science. The only hope is that there really will be some verifiable predictions that we could not anticipate without that quantum gravity theory.Certainly. I would hold that no problems of interpretation are physical problems, they are all philosophical. They will only be physical problems when interpretations spawn new theories that actually make testable predictions.
But Deutsch is missing the deeper undercurrent here-- for even if seasons were the same in the southern hemisphere, the Greek model would still be of no value! That's because the model predicts nothing, it is a perfect example of a pure rationalization. It makes no difference if the rationalization works, there is no way to verify that it is saying something they didn't already know unless it makes a prediction they would not otherwise expect-- no matter what is happening in the southern hemisphere.That's exactly my point, a theory must do more than rationalize what is already known, else there is no verification step. But this has nothing to do with realism or any other philosophical attachments, it is purely an issue of empirical evidence.
I don't see any distinction there, they both sound equally impossible to establish scientifically, and equally against the weight of scientific history. The world doesn't have to be "like" anything, it can just be what it is, and the theories can just work as well as they do, or do not. What more can be supported with evidence?
I agree, but look how much more difficult that question becomes if we must bury the Hamiltonian under the weight of being something that "the world must be really like." That approach forces an ontology onto the Hamiltonian, it can no longer be what it demonstrably is-- a mathematical concept, pure and simple, with no need to say anything more. We are playing the game of math, and we are doing it in a way that mimics or apes the presence of some Platonic "Hamiltonian", but the tension between the game and the ontology need not make any contact with a "true game that math really is", or a "true Hamiltonian that the world is really like." Those concepts are completely superfluous-- all we need is the interplay between the syntax of the game and the semantics of the ontology, without taking either one seriously as a destination of its own.
By all means, a thread exploring the purposes of the whole idea of having an ontology to prop up our thought processes would be quite interesting. It's relevant here as well though-- it's the reason that people like to imagine that math is Platonic, to have that prop.
And I would agree that both views have their value-- the truth is in the tension between them, structural realism has value because it invokes a tension between being a vacant solution, and an effective solution, and that tension opens up a discussion about what kinds of solutions we are looking for and why. We expect this as soon as we see that solutions are contextual and provisional, so the job of philosophy is not just to find the solutions, but also to clarify their limits.
But this invokes a false dichotomy. Now we must choose between our theories being either "not remotely true", or being "like the world". What happened to the most likely case of all, neither one? Why can't the theories just work pretty darn well for what they are supposed to work for, and yet not be anything "like" the actual truth of the world (if it even makes sense to talk about a truth of the world, which I argue it doesn't-- truths are contextual and provisional too). My assertion requires zero assumptions not in evidence, the standard naive realism requires a leap of faith that is contradicted every time the ontologies of our theories take another inevitable radical shift.
Actually, no induction whatever is required there. All that is required is the bedrock of science: basic skepticism. The requirement that a proposition be backed with evidence that is not constantly contradicted.
That's a basic requirement of the simple fact that it is known that Newtonian mechanics works well for some things, and relativistic mechanics works well for others. Same for quantum and classical. It is not saying anything surprising that a theory that worked for something will continue to work for that same something, so it is a given that all superior theories will "contain" the inferior versions. Something that must be true is not evidence for something that does not have to be true. We can take it as given that our theories work well, there is no other claim that can be made on nature without leaving the realm of what we can support with evidence.

josephwouk

I believe I understand QM.

I rely on this august group of physicists to disabuse me of my illusion.

I begin by assuming the two most accurate and proven theories in physics are correct; QM and general relativity.

1. Relativity says that we exist in a 4 dimensional universe that we apprehend as a 3 dimensional universe. Einstein believed that this was an "illusion."

2. It is the force of electromagnetism that causes us to think the universe is 3 dimensional. This is the force that defines matter as we experience it in its various forms. It is also the force that defines time. The constant speed of C is what defines how much time elapses for us depending on our own speed through space and/or the gravitational force we are subjected to. It is also the force that provides time with its arrow. The sum of the speed through space and the speed through time must always equal C. As C is the limit of speed through space, it is impossible for speed through time to be negative without requiring speed through space to exceed C.

3. Essentially, we live in a 3 dimensional subset of the 4 dimensional universe that is "knocked down" by the reality of electromagnetism, which we are made of and live under.

4. The Schrödinger equation describes particles as waves that permeate all of space-time, i.e. existing in a 4 dimensional "block universe" that we find particularly difficult to conceptualize.

5. Decoherence occurs when these waves encounter electromagnetic forces that compel them to appear as particles in that particular 3 dimensional subset. Information theory has shown that additional dimensions add enormously to the amount of information that can be held by any bit. This is why waves in 4 dimensions appear to us in 3 dimensions as particles. The old "Flatland" metaphor illustrates this perfectly.

6. "Measurement" is simply one way of forcing these waves to decohere. Consciousness has nothing whatsoever to do with it. We rely on the force of electromagnetism for any measurement we make.

7. Once decohered, these waves appear to us as particles in our 3 dimensional subset universe. They continue to behave as waves in the 4 dimensional block universe.

8. The wave nature of matter is necessitated by the relativity of simultaneity. Each observer's reality is equally valid, even though it doesn't agree with other observers traveling through space at a different speed or subjected to different gravitational forces. This truth would simply be impossible if matter were particles. Waves allow matter to appear anywhere in the 4 dimensional block universe where it happens to get decohered through the force of electromagnetism.

9. This is also why quantum indeterminacy is a foregone conclusion once one accepts the relativity of simultinaity.

Bottom line, if you believe relativity is correct, quantum "weirdness" is a necessary result. Without wave-particle duality and quantum indeterminacy, relativity would have to be wrong. With it, it works like a charm.

Please help me understand why the above has been proven to be incorrect.

I'm searching for experimentally proven facts to blow this "understanding" out of the water!

harrylin

Not exactly; "space is a three-dimensional continuum" - clarification here:
http://www.bartleby.com/173/17.html
"block universe discussion here:
http://physicsforums.com/showthread.php?t=567395
http://physicsforums.com/showthread.php?t=595021
The threads are still open for your comments.
Do you have a link? The only wave descriptions that I know are propagation in space as function of time - thus "3+1"D.
I'm afraid that I have never read something like that...
According to relativity, waves cannot propagate faster than c. Perhaps you overestimate what relativity of simultaneity can do. See: http://physicsforums.com/showthread.php?t=575332
First how SR works (and how it does not work) should be understood, and next the issue that "EPR" had with entanglement. And then Bell's theorem. After that, you could search for discussions about Bell inequality experiments end so.