Is something wrong with statistical interpretation of QM?

  • #26
All tests of Bell's inequalities support the results of quantum mechanics and are evidence against local hidden variables (at least local in the Bell sense).
Correct, but we don't have non-local(spooky action at a distance) forces/effects/technology/experiments that proves non-locality is a fact, similarly we don't have many-world technology where particles can be put in different worlds. Except, ofcourse in the Bell sense, where one of them must be correct if local hidden variables cannot produce the results.

Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?
 
  • #27
vanhees71
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There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.
 
  • #28
atyy
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Correct, but we don't have non-local(spooky action at a distance) forces/effects/technology/experiments that proves non-locality is a fact, similarly we don't have many-world technology where particles can be put in different worlds. Except, ofcourse in the Bell sense, where one of them must be correct if local hidden variables cannot produce the results.

Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?
The technical possibility remains that local realism is possible, because there is currently no loophole free experimental demonstration of a Bell inequality.

Even if there were, another technical possibility is superdeterminism.

Incidentally, Bell's inequality does not assume determinism.

If quantum mechanics is complete as in the many-worlds approach, no experimental violation of it will be found. If quantum mechanics arises from a nonlocal realistic hidden variables theory like de Broglie-Bohm, then in principle sufficiently advanced experiments could detect a violation of quantum mechanics.
 
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  • #29
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Now, it seems we have only three options,

a.) non-locality
b.) no definite reality
c.) formulation of bell's inequality using local hidden variables is not done correctly.

Noting the fact that ability of QM to produce statistical probabilities is mutually exclusive with bell's inequality, (i.e. correctness of QM does not guarantee correctness of bell's inequality). Which option would you choose?
(Did you mean that correctness of QM guarantees the incorrectness of Bell's inequality? The whole point of the exercise is that QM predicts violations of the inequality).

You're rehashing old and tired ground here.

We have enough analysis of Bell's work to relegate #c to the cranks and crackpots. So let's take that off the list.

Then let's add to the list #d - "none of the above". For example, superdeterminism keeps everything in the same light cone and assumes a definite reality, but does not suggest any incorrectness in the formulation of Bell's inequality and is not falsified by Aspect-type experiments.

However, all known #d candidates are either inconsistent with experiment or every bit as weird as #a or #b. So no matter which we choose, we're stuck with the weirdness. As long as there is no way of distinguishing #a, #b, and #d by experiment, the discussion is sterile.

(and eventually the moderators become impatient and close the thread on the reasonable grounds that no one is saying anything new.)
 
  • #30
There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.
Does it mean, it is non-realist theory? In a sense that we don't know the state of the particle prior to the measurement and therefore it is the measurement which produces the state right at the moment of measuring the property of the particle. And if after measurement we find some correlations, it is because they were introduced when the entangled particles were created.

All this does not seem very non-realist(except in the Bells sense), it seems very much classical, where we don't know which pair we have until we open the box, and since the pair is entangled when let's say, the pair of socks were packed in different boxes.

Where am I wrong?
 
  • #31
(Did you mean that correctness of QM guarantees the incorrectness of Bell's inequality? The whole point of the exercise is that QM predicts violations of the inequality).
All I meant was that correctness of Bell's inequality and correctness of quantum mechanics are mutually exclusive, in a sense one does not follow from other.

That is correctness of Bell's inequality is in Bells sense of local hidden variable, which is completely absent in QM.
 
  • #32
stevendaryl
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All this does not seem very non-realist(except in the Bells sense), it seems very much classical, where we don't know which pair we have until we open the box, and since the pair is entangled when let's say, the pair of socks were packed in different boxes.

Where am I wrong?
As I said, the difference is exactly Bell's sense. The kind of "entanglement" that exists classically can be explained as due to ignorance about the true state of the system. Quantum entanglement can't be viewed that way, according to Bel's theorem.
 
  • #33
stevendaryl
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There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.
Quantum field theory is very nice, in that it puts all the dynamics into the field operators, which evolve perfectly locally. This is the field-theoretic analog of the use of the Heisenberg picture in nonrelativistic quantum mechanics, where instead of having a wave function that evolves in time, the operators/observables evolve in time. The "equations of motion" for these operators look very much like the corresponding equations of motion for Newtonian physics, except that position and momentum are interpreted as operators, rather than real numbers.

In quantum field theory, the field operators are local operators and evolve according to field equations that are perfectly local. So everything is hunky dory.

But that doesn't really solve any of the interpretational problems of quantum mechanics. The problem is that the field operators don't describe any actual events (such as: a particle was detected at this place at this time). They, like the wavefunctions of nonrelativistic quantum mechanics, only give amplitudes for such events. So there is a gap between what the theory describes and what we actually observe in the world. It's the same gap as in nonrelativistic quantum mechanics. It either bothers you or it doesn't, but I think that there is no sense in which the questions of realism and locality and so forth that come up in nonrelativistic quantum mechanics are resolved by relativistic quantum field theory.
 
  • #34
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Until that happens, this is nothing more than a discussion on one's favorite color. And unless there is a high physics content in this discussion rather than just a discussion on one's personal preferences, this discussion is about philosophy and is subject to being closed.

Zz.

I hope that you don't actually believe that philosophy is "nothing more than a discussion on one's favorite color".

Physics is rooted in logic, and logic is a major branch of philosophy. Indeed, discussions of one's personal preferences have little or nothing to do with philosophy.
 
  • #35
DevilsAvocado
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Well, if we don't know how does it work, how can we be sure that QM is not wrong or incomplete.
Gosh... you asked for an intuitive explanation, in my world that's something different than a mathematical formulation, which to most "Average Joe" means pretty much nothing.

Furthermore, Bell's theorem is a no-go theorem, i.e. it states that L and R can't both be true – if Q is also true, and thus far no one has ever proven Q to be false.

So, we do have the mathematics describing entanglement and the shared wavefunction, and we can make prefect outcome predictions for all possible measurement settings, and it has worked perfectly for thousands of empirical experiments performed to this date, and there is absolutely nothing indicating that this will ever change in the future.

But we don't have all the answers; this doesn't mean QM is wrong or incomplete in any way.

Or does producing the statistical probabilistic outcome same as experiments, is more fundamental than let's say, what is the physics behind it?
Don't know what crystal ball you are tweaking to get to "the physics behind it", but out in the real world the most widespread method is experiments, experiments, experiments, and even more experiments. AFAIK, this is the only way to confirm the validity of a scientific theory.

Since a theory can only be complete when we know/understand how does it work, right?
Complete is a somewhat 'flexible' word that could change with history, and new knowledge. As for example in the 1935 EPR paper by Einstein, Podolsky and Rosen, they assumed that the principle of locality was "powerful to physical intuition", and defined a complete physical theory as one in which every element of physical reality is accounted for by the theory.

The 1935 EPR paper ends by:

While we have thus shown that the wave function does not provide a complete description of the physical reality, we left open the question of whether or not such a description exists. We believe, however, that such a theory is possible.

I.e. they drew the conclusion that quantum mechanics is not a complete theory.

I love Einstein, he was an absolute brilliant genius, but every rose has its thorns, and this time he was just simply wrong. In a historical perspective, the EPR paper backfired on him, and today we can be absolutely confident that classical local realism is not a complete 'theory' – it doesn't work in experiment!

I.e. even if QM some day is superseded by a new theory – local realism is already a dead parrot.

Period.
 
  • #36
DevilsAvocado
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Physics is rooted in logic, and logic is a major branch of philosophy.
Interesting that you brought up logic, unless I'm not mistaken, Gödel's incompleteness theorem shows that any system that is sufficiently powerful, such as arithmetic, cannot be both consistent and syntactically complete.

I sure hope that universal_101 is not claiming all of mathematics wrong, because of this little 'dilemma' ...
 
  • #37
WannabeNewton
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Where am I wrong?
Do you understand the difference between superposition and proper mixtures (classical ensembles)?
 
  • #38
DevilsAvocado
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Does it mean, it is non-realist theory? In a sense that we don't know the state of the particle prior to the measurement and therefore it is the measurement which produces the state right at the moment of measuring the property of the particle. And if after measurement we find some correlations, it is because they were introduced when the entangled particles were created.

All this does not seem very non-realist(except in the Bells sense), it seems very much classical, where we don't know which pair we have until we open the box, and since the pair is entangled when let's say, the pair of socks were packed in different boxes.

Where am I wrong?
You are not wrong, the quote is dead wrong, and stuck in the OLD 1935 PICTURE of perfect correlations of ONLY deterministic left/right, up/down, on/off, 1/0, etc.

This is exactly what Bell ERADICATED from the EPR paradox; to finally solve the 20+ year long Bohr–Einstein debates, by feasible experiments including extended/more measurement settings, giving results like up/up, down/down, up/down, down/up, in different amount to get correlations like cos2(22.5°) = 85%, producing this famous curve for settings 0° to 360°:

http://upload.wikimedia.org/wikipedia/en/thumb/e/e2/Bell.svg/500px-Bell.svg.png [Broken]
 
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  • #39
... and today we can be absolutely confident that classical local realism is not a complete 'theory' – it doesn't work in experiment!

I.e. even if QM some day is superseded by a new theory – local realism is already a dead parrot.

Period.
All the above in the Bells sense of local realism! right? That is if Bells theorem is proven wrong then there is nothing wrong with classical local realism. Additionally, it is your turn to prove that non-locality or non-realism in classical sense is violated.(Ofcourse using some other alternative approach)
 
  • #40
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That is if Bells theorem is proven wrong then there is nothing wrong with classical local realism. Additionally, it is your turn to prove that non-locality or non-realism in classical sense is violated.

No. You cannot start QM from the finish line and think you've arrived there the right way. You must start at the beginning and go the whole hog. Classical realism presupposes things that are not compatible with quantum theory and experiments.
 
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  • #42
Nugatory
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That is if Bells theorem is proven wrong then there is nothing wrong with classical local realism
well, yes... but do you seriously think that there is any possibility that Bell's theorem (that is, his proof of the theorem that the predictions of quantum mechanics cannot be reproduced by any member of the class of theories that make a particular assumption about the joint probability distribution of two observations) is wrong?

Or are you suggesting that there might be a theory that does not make that assumption and could still be recognizably local and realistic?
 
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  • #43
DevilsAvocado
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All the above in the Bells sense of local realism! right? That is if Bells theorem is proven wrong then there is nothing wrong with classical local realism. Additionally, it is your turn to prove that non-locality or non-realism in classical sense is violated.(Ofcourse using some other alternative approach)
Holy crap, yet another crackpot, if you continue along this cranky path this thread will be closed before the end of the day (local time).

Bell's theorem, in its simplest form, has a mathematical level just above primary school, but a gifted 10-yearold can without any problem grasp the meaning of it.

How old are you?

Do you understand that in our classical world 1 + 1 = 2?

Do you understand that Bell's theorem and QM proves experimentally that 1 + 1 = 3?

Do you understand that this is empirical evidence, that doesn't care about your personal preference?

Do you understand that empirical evidences never goes away, they will always be true, no matter what?

Do you understand that you are violating the rules of Physics Forums?
 
  • #44
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Why? is it because nature itself is inherently probabilistic since no classical hidden variable can explain Quantum entanglement, or is it because there are far too many degrees of freedom involved in any particular quantum measurement.
I was hopeing you would nut it out for yoursef, but didnt.

That nature is deterministic is no more a-priori than if its probabilitic. It is simply faulty reasoning to assume determinism is more reasonable - it isn't.

What Gleason's theorem proves, is if you take the first axiom of QM as found in Ballentine, namely the possible outcomes are the eigenvalues of the associated observable, is, with a few other reasonable assumptions such as basis independence (or equivalently non contextuality) then nature is inherently probabilistic. This was not put in from the start - it naturally popped out. Such is not true classically - determinism is simply assumed.

OK, let's see, Quantum entanglement according to quantum physics says the state of the two particles are said to be entangled, if they produce opposite (or similar depending on the experiment) results every time there is similar measurement done on the two particles state. But since the two states are not co-related according to QM(i.e they are independent of each other) therefore the only solution according to QM is that the two states somehow change the state of each other depending on what is measured on the other, to get the opposite/similar final results.
Hmmmm. That's very convoluted and tortured - its not quite that difficult.

Its got to do with the vector space structure of pure states in combined systems ie the principle of superposition.

Suppose you have two particles that can be in state |a> or state |b>. If particle 1 is in state |a> and particle 2 in state |b> then the system is in state |a>|b>. Conversely if particle 1 is in state |b> and particle 2 in state |a> then the system is in state |b>|a>. But the principle of superposition applies to each of those states so the system can be in say 1/2 |a>|b> + 1/2 |b>|a>. This means neither particle is in a specific state - they are entangled with each other. Such is inexplicable classically or by classical probability theory.

Thanks
Bill
 
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  • #45
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There is a third very unspectacular possibility: Local relativistic quantum field theory is correct! That's it. No problems left.
Good point.

That's the position of this guy:
https://www.amazon.com/dp/9812381767/?tag=pfamazon01-20&tag=pfamazon01-20

Interesting read as well.

Where am I wrong?
What Vanhees is saying is that QM is actually the limiting case of a deeper theory - QFT which is the combination of QM and relativity. Many of these issues are easily handled within QFT, the detail can be found in the book above.

Thanks
Bill
 
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  • #46
No. You cannot start QM from the finish line and think you've arrived there the right way. You must start at the beginning and go the whole hog. Classical realism presupposes things that are not compatible with quantum theory and experiments.
I agree that I should not do that, but bell's theorem is not about QM, it is about the failure of current classical local-realism to explain Quantum results. That is my point, that just because Quantum formulation produces the correct results and classical objectivity association with the state of the particle(which is purely a quantum non-real concept) does not produce the results which does not come under the domain of classical objectivism.

My point is why does Bell's theorem forces the classical objectivity to be applicable in Quantum mechanics, since the state of the particle is undefinable classically, therefore it is out of the scope of the classical physics and understandably should not produce good results. Now forcing classical objectivity on the state of the particle(which is purely a quantum non-real concept) should not infer that classical local-realism can never explain QM results. Instead one should infer that using the quantum concept of state(non-real) of a particle as a starting point, No classical theory can produce the same results.

I hope you see the difference!
 
  • #47
well, yes... but do you seriously think that there is any possibility that Bell's theorem (that is, his proof of the theorem that the predictions of quantum mechanics cannot be reproduced by any member of the class of theories that make a particular assumption about the joint probability distribution of two observations) is wrong?
There can't be more agreeable statement, and I don't think it is wrong when expressed like you did, very clearly. But I think, there is still hope for theories which does not make that assumption of joint probability distribution of two observations. Additionally, the above proof does not explicitly mean that non-locality or non-realism is a fact, it only means when a particular theory is used outside its domain of applicability, that particular theory does not produce good results.
Or are you suggesting that there might be a theory that does not make that assumption and could still be recognizably local and realistic?
I think there is a possibility, until we discover non-locality and/or non-realism independently.
 
  • #48
Holy crap, yet another crackpot, if you continue along this cranky path this thread will be closed before the end of the day (local time).

Bell's theorem, in its simplest form, has a mathematical level just above primary school, but a gifted 10-yearold can without any problem grasp the meaning of it.

How old are you?
No need to be jittery, we are just debating our views.
Do you understand that in our classical world 1 + 1 = 2?
Yes I do.
Do you understand that Bell's theorem and QM proves experimentally that 1 + 1 = 3?
That is the point, you can never prove 1+1 = 3(for a single description of nature), what you are doing is, equating the LHS(classical description of the state of the particle) to RHS(quantum statistical result), but ofcourse they should not be equal, for the two theories are not compatible.
Do you understand that this is empirical evidence, that doesn't care about your personal preference?
The Evidence that classical description of state of particle does not produce quantum statistical results, is perfectly understandable.
Do you understand that empirical evidences never goes away, they will always be true, no matter what?
Yes I do.
Do you understand that you are violating the rules of Physics Forums?
Is it because I used the phrase "Bell's theorem" and the word "wrong" in a single post.
 
  • #49
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My point is why does Bell's theorem forces the classical objectivity to be applicable in Quantum mechanics, since the state of the particle is undefinable classically, therefore it is out of the scope of the classical physics and understandably should not produce good results. Now forcing classical objectivity on the state of the particle(which is purely a quantum non-real concept) should not infer that classical local-realism can never explain QM results. Instead one should infer that using the quantum concept of state(non-real) of a particle as a starting point, No classical theory can produce the same results.

I hope you see the difference!
Nicely put. So if there are no classical hidden variables might there still there be quantum hidden variables?
 
  • #50
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Instead one should infer that using the quantum concept of state(non-real) of a particle as a starting point, No classical theory can produce the same results[/I].

I hope you see the difference!


There is simply no other concept of 'particles' than the quantum states of the formalism. That's why they are the starting point.

You seem to tacitly assume that there may exist some other classically real stuff that may in 1028 years explain the correlations but unless you can provide evidence for that, you are threading a very narrow crackpotish path here. You are criticizing a hundred years of physics for allegedly incorrectly using the concept of quantum states and your justification for that is what? A hunch?

What is your starting point if quantum states are not to be used as a description of matter? A unicorn? Quantum theory is not a hoax and can't be overturned by bad philosophy.
 
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