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The Trouble with Quantum Mechanics

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Re: The Trouble with Quantum Mechanics

#91

Post by lisper »

beevai142 wrote: post #90
lisper wrote: post #82

Earlier quoted context omitted.

> in the end it is philosophically just the Copenhagen interpretation No, it isn't. The wave function never collapses. This is easily demonstrated with a simple thought experiment which is described in the first two references that I link to.

I wrote about the interpretation usually used in published papers, and obviously decoherence alone does not solve the measurement problem as it only shuffles it to the bigger system, you need many worlds / Copenhagen / etc. I don't bother watching youtube videos of what someone thinks quantum mechanics is about.

You don't have to watch a video. My first reference is to a paper.

Re: The Trouble with Quantum Mechanics

#92

Post by tim333 »

lisper wrote: post #80
tim333 wrote: post #72

Earlier quoted context omitted.

Indeed it's not that solved. A big problem is as Weinberg puts it >Several attempts following the realist approach have come close to deducing rules like the Born rule that we know work well experimentally, but I think without final success. which is kind of the heart of things.

Just because Steven Weinberg is unaware of or does not accept the solution does not mean that the problem is not in fact solved.

I don't think that's been solved either or most physicists for that matter. I've read some of the attempts and they are not terrible good.

I don't think Ron Garret even touched on the Born rule, Everett of many worlds just hand waves and assumes it. The attempts I've seen are basically of the form that if the rule was different from the probability equaling the absolute amplitude squared then reality wouldn't come out as we find, so it must be so, which is not much of an explanation in my book.

Re: The Trouble with Quantum Mechanics

#93

Post by akvadrako »

beevai142 wrote: post #90
lisper wrote: post #82

Earlier quoted context omitted.

> in the end it is philosophically just the Copenhagen interpretation No, it isn't. The wave function never collapses. This is easily demonstrated with a simple thought experiment which is described in the first two references that I link to.

I wrote about the interpretation usually used in published papers, and obviously decoherence alone does not solve the measurement problem as it only shuffles it to the bigger system, you need many worlds / Copenhagen / etc. I don't bother watching youtube videos of what someone thinks quantum mechanics is about.

Many worlds is just a way of describing the results of entanglement. It doesn't add any structure or dynamics to the wave function. Those worlds are precisely those slices the parent is talking about.

Re: The Trouble with Quantum Mechanics

#94

Post by akvadrako »

opaque wrote: post #66
lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

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…

> At least not to the satisfaction of most practising physicists.

This is true, as the parent said - it's not accepted by many physicists.

> However, it requires you to make a pretty arbitrary division between the observed system and the wider environment.

This isn't true. The whole universe is in a superposition and you can reason with decoherence at any level. Literally everything in one "world" including the vacuum of space is entangled with everything else, though to a very small degree.

Re: The Trouble with Quantum Mechanics

#95

Post by tigershark »

lisper wrote: post #80
tim333 wrote: post #72

Earlier quoted context omitted.

Indeed it's not that solved. A big problem is as Weinberg puts it >Several attempts following the realist approach have come close to deducing rules like the Born rule that we know work well experimentally, but I think without final success. which is kind of the heart of things.

Just because Steven Weinberg is unaware of or does not accept the solution does not mean that the problem is not in fact solved.

If you are religiously convinced that the QIT interpretation is the only true one that doesn't make it true. For me it is just one of the many interpretations and I think that it is wrong on par with all the others that I'm aware of. If this wasn't the case then the measurement problem and the unification with the relativity theory (or with a theory that supersedes the relativity) would be already solved today. I'm really not in the field, but I don't think that anyone that actively works on QM is debating on solved problems.

Re: The Trouble with Quantum Mechanics

#96

Post by akvadrako »

tim333 wrote: post #72
n4r9 wrote: post #65

Earlier quoted context omitted.

> The measurement problem is a solved problem. I think this is overselling it slightly. Yes, Everettian style interpretations have helped to shed insight into the reality of the quantum state. Yes, decoherence has helped us to understand physical systems and their interactions with the environment. But if the measurement problem was solved there wouldn't continue to be a swathe of literature on the measurement proble…

Indeed it's not that solved. A big problem is as Weinberg puts it >Several attempts following the realist approach have come close to deducing rules like the Born rule that we know work well experimentally, but I think without final success. which is kind of the heart of things.

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 probability inside a deterministic system (the wave function). One thing QM shows us is that we experience real random events, which cannot just come from lack of knowledge. Yet, if you are a computer expert you should know that it's impossible to create real randomness without an outside source. And the universe has no outside sources at all, by definition.

Also, it's clear that the basis of Weinberg's objection to WMI is philosophical if you don't selectively quote him so much. If he was concerned about deriving the Born rule we would talk about the specific assumptions he disagrees with.

Re: The Trouble with Quantum Mechanics

#97

Post by lisper »

tim333 wrote: post #92
lisper wrote: post #80

Earlier quoted context omitted.

Just because Steven Weinberg is unaware of or does not accept the solution does not mean that the problem is not in fact solved.

I don't think that's been solved either or most physicists for that matter. I've read some of the attempts and they are not terrible good. I don't think Ron Garret even touched on the Born rule, Everett of many worlds just hand waves and assumes it. The attempts I've seen are basically of the form that if the rule was different from the probability equaling the absolute amplitude squared then reality wouldn't come ou…

FYI, I am Ron Garret.

It's true that I don't talk about the Born rule or multiple worlds in the paper, but I do talk about multiple worlds in the video (at the end, during the Q&A) and in the blog posts I linked to above.

As for the Born rule, what kind of an explanation are you hoping for? Some things can't be explained beyond, "That's just how it is." For example, why do the fundamental physical constants have the values that they have?

Maybe this will help:

https://news.ycombinator.com/item?id=13406241

http://www.scottaaronson.com/democritus/lec9.html

Re: The Trouble with Quantum Mechanics

#98

Post by lisper »

tigershark wrote: post #95
lisper wrote: post #80

Earlier quoted context omitted.

Just because Steven Weinberg is unaware of or does not accept the solution does not mean that the problem is not in fact solved.

If you are religiously convinced that the QIT interpretation is the only true one that doesn't make it true. For me it is just one of the many interpretations and I think that it is wrong on par with all the others that I'm aware of. If this wasn't the case then the measurement problem and the unification with the relativity theory (or with a theory that supersedes the relativity) would be already solved today. I'm r…

I am absolutely not religiously convinced that QIT is the only true explanation. In fact, I explicitly say at the end of my talk that it is not, that multiple-worlds is equally valid, and which you choose is a matter of personal preference. But if want to argue that no solution exists (and this is Weinberg's claim) then you have to consider all of the solutions on the table, and Weinberg does not. He deliberately ignores the fundamental (and IMHO ultimately clarifying) fact that entanglement and measurement are intimately related (and are in fact the same physical phenomenon). It is entirely unsurprising that anyone who ignores this fact ends up believing that there is a big mystery. But in fact there is no big mystery. There are only people who are mystified because they are ignoring (or ignorant of) this crucial fact.

Re: The Trouble with Quantum Mechanics

#99

Post by [deleted] »

lisper wrote: post #91
beevai142 wrote: post #90

Earlier quoted context omitted.

I wrote about the interpretation usually used in published papers, and obviously decoherence alone does not solve the measurement problem as it only shuffles it to the bigger system, you need many worlds / Copenhagen / etc. I don't bother watching youtube videos of what someone thinks quantum mechanics is about.

You don't have to watch a video. My first reference is to a paper.

[deleted]

Re: The Trouble with Quantum Mechanics

#100

Post by akvadrako »

gaze wrote: post #86
lisper wrote: post #59

This article presents a very inaccurate view of the realist approach. The universe does not "split" when you make a measurement. The measurement problem is a solved problem. The solution is that measurement and entanglement are the same physical phenomenon. Measurement is just entanglement extended to a macroscopic system through a process called "decoherence". The net result is that, when you do the math, you recove…

This is going in circles. You still need to put in Born's rule by hand somewhere. If you can explain the origin of Born's rule we'll have gotten somewhere. I also don't understand why you call a trace a slice. It's an ensemble average. Try deriving the density matrix formalism by coupling a small system to some collection of ancillae and you'll see that it doesn't really add anything. The trace is just convenient not…

There are a few ways to derive the Born rule within WMI. None are perfect but their assumptions are fairly reasonable and most importantly the handling of probability is better defined than in classical mechanics or Copenhagen, so it's not a reason to discount the theory.

https://en.wikipedia.org/wiki/Many-worlds_interpretation#Pro...

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