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The Trouble with Quantum Mechanics

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Re: The Trouble with Quantum Mechanics

#111

Post by akvadrako »

n4r9 wrote: post #109
akvadrako wrote: post #96

Earlier quoted context omitted.

I know of 3 modern ways to derive the Born rule for WMI and all have various reasonable (yet not airtight) assumptions. In physics you can never really prove anything, but there is no serious technical issues here. Actually probability (the Born rule) is much better defined in WMI then in any other interpretation or even classically. A related beautiful thing about WMI is that is creates genuine subjective probabilit…

Have you aware of Adrian Kent's critiques of (many of) these attempts? https://arxiv.org/abs/0905.0624

I have read lots of critiques about the Born rule derivations but I've missed this one. Thanks for the pointer. He is only attacking one attempt, the decision-theoretic one.

I have trouble finding his point in this paper because it's so rambling but he seems to be saying:

> It seems prima facie surprising to claim that mathematical analysis could show that Born-weight mean utilitarianism, or any other strategy, is the unique rational way of optimizing the welfare of one’s own, and other people’s, many future selves in a multiverse.

Okay, sure - but it's also just as ridiculous to say that you can prove with no assumptions how a rational agent should act in a classical world.

Actually there is no explanation of probability in the classical world that's as clear as that in a multiverse, where you have actual proportions of outcomes.

All you really need is to assume that branches of equal magnitude have an equal chance of occurring and the Born rule becomes obvious. That seems like a safe assumption to me but you can't prove it beyond all doubt without some axioms of probability.

EDIT: I found a critique of his paper you might also want to read: https://arxiv.org/pdf/1111.2563.pdf

Re: The Trouble with Quantum Mechanics

#112

Post by [deleted] »

n4r9 wrote: post #109
akvadrako wrote: post #96

Earlier quoted context omitted.

I know of 3 modern ways to derive the Born rule for WMI and all have various reasonable (yet not airtight) assumptions. In physics you can never really prove anything, but there is no serious technical issues here. Actually probability (the Born rule) is much better defined in WMI then in any other interpretation or even classically. A related beautiful thing about WMI is that is creates genuine subjective probabilit…

Have you aware of Adrian Kent's critiques of (many of) these attempts? https://arxiv.org/abs/0905.0624

[deleted]

Re: The Trouble with Quantum Mechanics

#113

Post by opaque »

lisper wrote: post #79
opaque wrote: post #66

Earlier quoted context omitted.

Decoherence is an extremely useful and elegant mechanism for understanding quantum systems, but unfortunately it doesn't solve the measurement problem. At least not to the satisfaction of most practising physicists. The entanglement and trace operation does produce classical probabilities in the observed sub-system. However, it requires you to make a pretty arbitrary division between the observed system and the wider…

> Why is everything not just entangled with everything else up and up the chain until the entire universe is in superposition? It is. I'm going hazard a guess that your next question is going to be: why do I not perceive myself to be in a superposition of states? And the answer is that you are not what you think you are. You think you are a human being, a classical physical object made of atoms, but you aren't. This…

Clearly you have your own unorthodox interpretation of quantum mechanics and you are quite emotionally attached to it. The argument that the universe is really X, but your brain just perceives it as Y because of Z can be made for any X,Y & Z. I don't find it compelling whatever the alleged reason for the disparity (in this case the no cloning theorem). There's also whole host of other issues, if everything is QM why has the brain evolved as a classical information processor, QM is unitary so you need to explain time/thermodynamics ...

Anyway, if you truly believe you have nailed both the measurement problem and consciousness in one fell swoop. Then I suggest you seek some like minded collaborators and a peer reviewed outlet for your ideas.

Returning to your original comment.

> It is astonishing to me that the physics community still bifurcates into two camps: those who think this is common knowledge, and those who are completely unaware of it (or think it's a crazy idea).

As a former member of the physics community I can tell you this is completely false. Everyone is aware of decoherence, it's covered toward the end most of undergrad courses in QM where the density matrix is introduced. I've never met anyone who thinks it solves the measurement problem.

Re: The Trouble with Quantum Mechanics

#114

Post by n4r9 »

akvadrako wrote: post #111
n4r9 wrote: post #109

Earlier quoted context omitted.

Have you aware of Adrian Kent's critiques of (many of) these attempts? https://arxiv.org/abs/0905.0624

I have read lots of critiques about the Born rule derivations but I've missed this one. Thanks for the pointer. He is only attacking one attempt, the decision-theoretic one. I have trouble finding his point in this paper because it's so rambling but he seems to be saying: > It seems prima facie surprising to claim that mathematical analysis could show that Born-weight mean utilitarianism, or any other strategy, is th…

I'm not sure what you mean by "safe". My understanding of Kent's objection is that there's no explanation for why the norm-squared magnitude is related to probability in the first place.

Re: The Trouble with Quantum Mechanics

#115

Post by akvadrako »

n4r9 wrote: post #114
akvadrako wrote: post #111

Earlier quoted context omitted.

I have read lots of critiques about the Born rule derivations but I've missed this one. Thanks for the pointer. He is only attacking one attempt, the decision-theoretic one. I have trouble finding his point in this paper because it's so rambling but he seems to be saying: > It seems prima facie surprising to claim that mathematical analysis could show that Born-weight mean utilitarianism, or any other strategy, is th…

I'm not sure what you mean by "safe". My understanding of Kent's objection is that there's no explanation for why the norm-squared magnitude is related to probability in the first place.

The simplest way to derive the Born rule is to assume "branches" of equal magnitude have equal chances of happening. This isn't controversial because it's a very basic part of QM that is demonstrated by experiments and it seems quite natural too.

Yet even that assumption above can be weakened - that's what the derivations are trying to show to the critics because they find WMI so hard to accept for unrelated reasons.

This is in contrast to the situation in collapse interpretations where the Born rule itself is simply postulated. And in classical mechanics, we need to resort to frequentist explanations which are pretty weak.

So we have already gone quite far beyond the best explanations of probability in any other system.

Re: The Trouble with Quantum Mechanics

#116

Post by lisivka »

krastanov wrote: post #106
lisivka wrote: post #104

Earlier quoted context omitted.

Lets define experiment as following (excuse me my bad English, please): - vibrating bath with non-conductive, non-magnetic, non-paramagnetic, non-diamagnetic fluid; - vibrating bath is wide enough to avoid excessive interference with reflected waves from bath sides; - vibrating bath has regular pattern on top of fluid, without any irregularities in space of experiment; - small charged droplets of fluid on top of bath…

The main point of the Stern-Gerlach experiment was that the electrons hitting the screen were forming two distinct dots instead of a long spread out line, therefore proving that the angular momentum is quantised. In your example you will instead have simply a spread-out distribution because there is no quantisation of the angular momentum of your droplets. The pilot wave usually refers to the spatial degrees of freed…

IMHO, Stern-Gerlach experiment demonstrates interaction of magnet field with guiding wave mediated via particle, so I expect that magnet will steer particle-wave into same spots, thus will demonstrate «quantum» behavior of particle spin at macro level.

Re: The Trouble with Quantum Mechanics

#117

Post by lisper »

akvadrako wrote: post #110
lisper wrote: post #107

Earlier quoted context omitted.

> These things are not unrelated :) If you accept that there is only the wave function as in the bare formalism, either an infinity of worlds or zero worlds, like in QIT, are the logical outcomes. Yep. > But I am not saying they "have to" - I'm saying that is their reason for not accepting the bare formalism. Well, OK, but then the burden is on them to come up with something better. QM is one of the most thoroughly t…

Maybe I agree with you, but science is built on philosophy, which is not rigorous - but based on fuzzy feelings of what is right. The fact that we accept QM because it predicts the outcome of experiments is philosophy. So I could theoretically imagine someone holding the belief in our universe being what it seems higher than mathematical sense. Yet my primary point is physicists are just human and have all the same i…

In your everyday experience, you are constantly bombarded with overwhelming evidence that space and time are two completely different things, that matter and energy are two completely different things, that life is much too complex and well adapted to its environment to have arisen without an intelligent designer, and that the sun revolves around the earth. And yet, none of these things are true.

Likewise, you are constantly bombarded with overwhelming evidence that you are a classical physical entity living in a classical universe. But that is not true either. It's a very good approximation to the truth, good enough for most day-to-day purposes, but it is not the truth.

You can choose to accept these facts, or you can choose to bury your head in the sand. But you cannot legitimately say that there is a "problem with quantum mechanics" when in fact what is going on is that you have chosen to bury your head in the sand. There is no more a "problem" with quantum mechanics than there is a "problem" with relativity, evolution, or the Copernican theory. There is no intractable mystery here, only people who choose not to accept what the math is telling them.

Re: The Trouble with Quantum Mechanics

#118

Post by lisper »

opaque wrote: post #113
lisper wrote: post #79

Earlier quoted context omitted.

> Why is everything not just entangled with everything else up and up the chain until the entire universe is in superposition? It is. I'm going hazard a guess that your next question is going to be: why do I not perceive myself to be in a superposition of states? And the answer is that you are not what you think you are. You think you are a human being, a classical physical object made of atoms, but you aren't. This…

Clearly you have your own unorthodox interpretation of quantum mechanics and you are quite emotionally attached to it. The argument that the universe is really X, but your brain just perceives it as Y because of Z can be made for any X,Y & Z. I don't find it compelling whatever the alleged reason for the disparity (in this case the no cloning theorem). There's also whole host of other issues, if everything is QM why…

> Clearly you have your own unorthodox interpretation of quantum mechanics

None of these ideas are original with me. All of them can be found in the literature. My only contribution (if I've made a contribution at all) is pedagogical.

> and you are quite emotionally attached to it.

Yes, I am quite emotionally attached to the truth. And yes, it does annoy when people promulgate the myth that QM is hard to understand or contains intractable mysteries when I know it isn't true. It particularly annoys me when people say this and simultaneously ignore the incontestable fact that entanglement and measurement are the same thing, in the same sense that space and time are the same and matter and energy are the same. Yes, all of these things are weird, and yet all of these things are true, and none of them are intractable mysteries or even hard to understand.

> I suggest you seek some like minded collaborators and a peer reviewed outlet for your ideas.

Like I said, these aren't my ideas. But I did submit my paper to Physics Today back when I first wrote it in 2001. It was rejected on the grounds that everything in it was already common knowledge.

> As a former member of the physics community I can tell you this is completely false. Everyone is aware of decoherence

But obviously not everyone is aware of its implications. Your challenging me on this is manifest evidence of that. And for 25 years I have been stumping card-carrying physicists with the EPRG thought experiment. Heck, it took me ten years to find anyone in the physics community who knew the answer! (I even had a chance to pose the question to Freeman Dyson, and he didn't know the answer!)

Re: The Trouble with Quantum Mechanics

#119

Post by n4r9 »

akvadrako wrote: post #115
n4r9 wrote: post #114

Earlier quoted context omitted.

I'm not sure what you mean by "safe". My understanding of Kent's objection is that there's no explanation for why the norm-squared magnitude is related to probability in the first place.

The simplest way to derive the Born rule is to assume "branches" of equal magnitude have equal chances of happening. This isn't controversial because it's a very basic part of QM that is demonstrated by experiments and it seems quite natural too. Yet even that assumption above can be weakened - that's what the derivations are trying to show to the critics because they find WMI so hard to accept for unrelated reasons.…

It is kinda controversial. At least in relation to MWI; the validity and meaning of that assumption forms the basis of much of the criticism of MWI. If there were a rigorous derivation of the Born rule as a logical consequence of a global state undergoing unitary evolution, then I and many others would be much more convinced.

The other part of the problem is how/why observational outcomes occur in a probabilistic fashion in the first place. You keep saying that one or other branch "occurs" or "happens", but in MWI they're all happening. For some reason the observer only experiences one particular strand of their own superposition, and with a somewhat arbitrary probability to boot. It's not like that's the strand they're "actually in" but ignorant of. This is very different from subjective knowledge of a deterministic universe.

Re: The Trouble with Quantum Mechanics

#120

Post by krastanov »

lisivka wrote: post #116
krastanov wrote: post #106

Earlier quoted context omitted.

The main point of the Stern-Gerlach experiment was that the electrons hitting the screen were forming two distinct dots instead of a long spread out line, therefore proving that the angular momentum is quantised. In your example you will instead have simply a spread-out distribution because there is no quantisation of the angular momentum of your droplets. The pilot wave usually refers to the spatial degrees of freed…

IMHO, Stern-Gerlach experiment demonstrates interaction of magnet field with guiding wave mediated via particle, so I expect that magnet will steer particle-wave into same spots, thus will demonstrate «quantum» behavior of particle spin at macro level.

Without disrespect I insist that you are wrong about that. The spin degree of freedom is "internal", unrelated to the position of the particle. The pilot wave does not influence that spin, and if you have a big ball on top of a wave, that wave does not care about the angular momentum of the ball. The ball is big and classical, hence its angular momentum is (practically) not quantized.

The thread got a bit long, but if you are really interested in learning about this I would be happy to continue the discussion through email (stefan.krastanov@yale.edu). You probably also need proof of some kind of qualification on my part - my online profile does prove that I work at a respected institute doing research on that topic.

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