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The Trouble with Quantum Mechanics

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Re: The Trouble with Quantum Mechanics

#81

Post by lisper »

iheartmemcache wrote: post #64
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…

Well the Copenhagen interpretation traditionally requires the act of an 'observer'. I.e., you are not allowed to perform that act of summation on the set of orthonormal vectors in N dimensional Hilbert spaces until an "observer" observes . (That's where that stupid cat came into play and the 'uncertainty' of it being both dead and alive simultaneously until it's 'observed'.) Until this discrete event occurs, the wave…

The wave function never collapses. This is easily demonstrated with a simple thought experiment that is described in the first two references that I link to.

Re: The Trouble with Quantum Mechanics

#82

Post by lisper »

beevai142 wrote: post #70
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…

This is correct. As it is usually applied in practice in the literature, the measurement device decoheres the quantum system and becomes entangled with it --- and at the end of the calculation, Copenhagen interpretation is applied on the measurement device. It works fine in practice, but in the end it is philosophically just the Copenhagen interpretation. If something is not accepted by the wider physics community, i…

> 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.

Re: The Trouble with Quantum Mechanics

#83

Post by lisivka »

krastanov wrote: post #77
lisivka wrote: post #62

Earlier quoted context omitted.

So, your prediction for walker droplet spin is that walkers, in kind of Stern and Gerlach experiment, will behave like classical magnets, not like quantum particles, right?

No, they would behave like a ball floating on top of a wave and given that there are waves involved there will also be interference patterns. There is nothing quantum here. Sure, in one particular way it looks like a quantum particle (to the extent of a cargo cult), but in all the important ways it does not (entanglement, computational power, generalisation to multiple particles).

I asking about outcome of Stern and Gerlach experiment. It's binary thing. Make public prediction, please.

Re: The Trouble with Quantum Mechanics

#84

Post by FrostyElsa »

lisper wrote: post #82
beevai142 wrote: post #70

Earlier quoted context omitted.

This is correct. As it is usually applied in practice in the literature, the measurement device decoheres the quantum system and becomes entangled with it --- and at the end of the calculation, Copenhagen interpretation is applied on the measurement device. It works fine in practice, but in the end it is philosophically just the Copenhagen interpretation. If something is not accepted by the wider physics community, i…

> 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.

People are so dumbfounded by the Everettian interpretation. It may take more time (with Quantum computing help) to prove that the wave function indeed never collapses and that there are infinite number of probabilistic worlds in actual existence.

Hello graveyardigans.

Re: The Trouble with Quantum Mechanics

#85

Post by lisivka »

gizmo686 wrote: post #78
lisivka wrote: post #73

Earlier quoted context omitted.

No, it's not a time travel. Bob will see that Carol travels backward and Carol will see that Bob travel backward, like we see EM emission from FTL electron in reverse order. FTL electron is not moving back in time, nor Bob or Carol.

The notion of "backwards" in time is a bit fuzzy once you get into relativity, so the three person example I gave may not clearly show it. However, in the four person example, Dave is able to hand Carol her diary of the trip that she is about to make. If that is not time travel, I do not know what is.

It's very unlikely. If Dave has Carol diary, then Carol made the trip already, so Carol will notice empty fuel tanks and big holes in the shield. She will may have problems with memory, but she is not stupid.

Re: The Trouble with Quantum Mechanics

#86

Post by gaze »

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 notation for the operator sandwich of closed quantum systems... it's just that your closed system is now an open system tensored with a bath.

Re: The Trouble with Quantum Mechanics

#87

Post by gizmo686 »

lisivka wrote: post #85
gizmo686 wrote: post #78

Earlier quoted context omitted.

The notion of "backwards" in time is a bit fuzzy once you get into relativity, so the three person example I gave may not clearly show it. However, in the four person example, Dave is able to hand Carol her diary of the trip that she is about to make. If that is not time travel, I do not know what is.

It's very unlikely. If Dave has Carol diary, then Carol made the trip already, so Carol will notice empty fuel tanks and big holes in the shield. She will may have problems with memory, but she is not stupid.

No she didn't. X is the point in spacetime where Carol begins her trip. From her perspective, Dave came from the future.

The only reason that this cannot happen is that X and Y are so far away in space, and close in time, that it is impossible to travel between them.

Re: The Trouble with Quantum Mechanics

#88

Post by lisper »

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…

> You still need to put in Born's rule by hand somewhere

I'm not sure what you mean by "putting Born's rule in by hand". We're talking about interpretations here. Born's rule is just an empirical fact. Do you mean that I need to explain why the probabilities are the square of the amplitude? That's kind of like asking me to explain why the speed of light has the value that it has. It doesn't have an explanation. It's just part of the Way Things Are.

But I can make the following heuristic arguments:

1. Outcomes are probabilistic because this is the only way that classical behavior can emerge from the wave function, and without classical behavior you can't copy information, and without copying information you can't have discussions like the one we're having. It's an anthropomorphic argument (actually it's a info-pomomorphic argument :-)

2. The probabilities are the square of the amplitude because that is how you get a useful mathematical model of reality. It is simply an empirical fact that destructive interference happens, so if you want to build a mathematical model of that you need something that can take on negative values. You can't have negative probabilities in classical reality, so the underlying reality must be something other than classical probabilities. The square root of the probability is just the simplest mathematical model that explains the observations.

Maybe this will help: the technical paper that my position is based on is here:

https://arxiv.org/pdf/quant-ph/9605002v2.pdf

Re: The Trouble with Quantum Mechanics

#89

Post by krastanov »

lisivka wrote: post #83
krastanov wrote: post #77

Earlier quoted context omitted.

No, they would behave like a ball floating on top of a wave and given that there are waves involved there will also be interference patterns. There is nothing quantum here. Sure, in one particular way it looks like a quantum particle (to the extent of a cargo cult), but in all the important ways it does not (entanglement, computational power, generalisation to multiple particles).

I asking about outcome of Stern and Gerlach experiment. It's binary thing. Make public prediction, please.

Certainly, but then please first pose/define the question clearly. What do you call a macroscopic Stern-Gerlach experiment with balls floating on top of the waves of a fluid? It would be an amusing toy problem to work out if you define it for me. However, it does not change the main argument: there is nothing quantum in macroscopic experiments with water waves - interference does not imply "quantumness".

Re: The Trouble with Quantum Mechanics

#90

Post by beevai142 »

lisper wrote: post #82
beevai142 wrote: post #70

Earlier quoted context omitted.

This is correct. As it is usually applied in practice in the literature, the measurement device decoheres the quantum system and becomes entangled with it --- and at the end of the calculation, Copenhagen interpretation is applied on the measurement device. It works fine in practice, but in the end it is philosophically just the Copenhagen interpretation. If something is not accepted by the wider physics community, i…

> 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.

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