Common misconceptions regarding quantum mechanics

[Edgardo]

Hello all,

you may find this paper
http://www.oberlin.edu/physics/dstyer/TeachQM/misconnzz.pdf
interesting. It describes common misconceptions in quantum mechanics.

It's free accessible. It also appeared on the American Journal of physics.

Daniel F. Styer, "Common misconceptions regarding quantum mechanics", American Journal of Physics, 64 (1996) 31-34, 1202.

You may also want to browse through Styer's website:
http://www.oberlin.edu/physics/dstyer/TeachQM/
http://www.oberlin.edu/physics/dstyer/

with interesting topics like:
# Solving Problems in Physics
# Study Tips for Introductory Physics Students


Cheers!

- Edgardo

 

[bcbwilla]

Funny, I just read this paper, and so I came to these forums to share it, but upon searching for a link to the paper to post in the new thread I was creating I found a link to here!


Anyway, I know most forums don't appreciate resurrecting old topics, but I found this paper interesting as an undergraduate taking my first real QM course so I think it's worth a bump.

 

[Demystifier]

Nice paper!

For some more advanced common misconceptions in QM see also
http://xxx.lanl.gov/abs/quant-ph/0609163 [Found.Phys.37:1563-1611,2007].

 

[Mordred]

your right the paper does warrent a bump very handy

 

[Drakkith]

Excellent read, even if I didn't understand the math and all.

 

[jfy4]

it dismisses the recognition of the state vector as an ensemble interpretation even though I felt Ballentine made a good case for that interpretation. He also then cites Bell's theorem as the cause for objection, are there any other papers that demonstrate or make a case as to why we should dismiss the ensemble interpretation?

 

[zonde]

it dismisses the recognition of the state vector as an ensemble interpretation even though I felt Ballentine made a good case for that interpretation. He also then cites Bell's theorem as the cause for objection, are there any other papers that demonstrate or make a case as to why we should dismiss the ensemble interpretation?

Can't say about papers that criticize ensemble interpretations but I have tried to make a case why ensemble interpretations should not be dismissed because of Bell. For no better option I put it on vixra.

 

[Fredrik]

it dismisses the recognition of the state vector as an ensemble interpretation even though I felt Ballentine made a good case for that interpretation. He also then cites Bell's theorem as the cause for objection, are there any other papers that demonstrate or make a case as to why we should dismiss the ensemble interpretation?

Bell inequality violations imply that a superposition of spin up and spin down is different from an ensemble in which some of the particles are in the spin up state and some in the spin down state. This certainly doesn't refute the interpretation-independent fact that a state vector is an extremely accurate representation of the properties of the ensemble that consists of the particles on which the measurements are performed when we run the experiment over and over. (The difference between interpretations is what other meanings they assign to state vectors. The ensemble interpretation can be defined by the postulate that a state vector doesn't actually describe anything else).

 

[vanhees71]

I haven't read the paper yet. Can you briefly summarize the objection against the Minimal Statistical Interpretation (MSI) from the observed violation of Bell's inequality? For me, to the contrary, this is the strongest argument for and not against the MSI!

Look at what's done to show this violation experimentally: One always observes ensembles and does statistics on them!

 

[Fredrik]

The paper doesn't really make an argument. It just claims that Bell inequality violations imply that a quantum superposition doesn't accurately describe an ensemble of classical systems.

Edit: To be more precise, it said exactly this:

5. "A wavefunction (or state vector) describes an ensemble of classical systems." In the standard Copenhagen interpretation, a state vector describes a single system, e.g. a single particle or, in systems such as the hydrogen atom, a single pair of particles. In tenable statistical interpretations [8], the state vector describes an ensemble of individual systems each of which does not behave classically. The appealing view that a state vector represents an ensemble of classical systems was rendered untenable by tests of Bell's theorem [9], which show that no deterministic1 model, no matter how complicated, can give rise to all the results of quantum mechanics.​

Note that he's not arguing against what he calls "tenable statistical interpretations". Reference [8] is an article by Ballentine that I haven't read.

 

[vanhees71]

A quantum state describes a system. Whether its behavior can be appropriately approximated by classical (statistical) physics depends on the system and the state. If you have entangled subsystems and make measurements of corresponding correlations, of course you cannot describe these correlations within classical systems. This is a situation far away from classical behavior, but that doesn't contradict the Minimal Statistical Interpretation.

 

[Fredrik]

A quantum state describes a system.

If you define the word "describes" by saying that this statement means that the state can be used to make accurate predictions about experiments, then yes. But we already have an intuitive understanding of what "describes" means, so it's kind of weird to turn it into a technical term like that. If we take "describes" as a primitive (a term left undefined), and continue to rely on our intuitive understanding of what it means, then your statement is actually rather controversial. It would be a good starting point for a MWI, or an interpretation that says that classical logic must be replaced with quantum logic, but not for a statistical interpretation.

 

[KWillets]

I was curious what he meant by "deterministic1 model", so I read the paper, and the erratum states that "local deterministic model" was intended there, a fairly crucial typo. Perhaps that's what he means by classical system?

I don't think he's trying to revise interpretations here, just point out how people can alight on determinism without realizing the nonlocal aspects.

 

[Thenewdeal38]

The biggest one in pop culture. Quantum Physics has something to do with conscieness and or makes your thoughts gradually become real.

 

[Demystifier]

The biggest one in pop culture. Quantum Physics has something to do with conscieness and or makes your thoughts gradually become real.

That one is big, but I think the following one is even bigger:
Real particles communicate by exchanging virtual particles.

 

[BWV]

Nice paper!

For some more advanced common misconceptions in QM see also
http://xxx.lanl.gov/abs/quant-ph/0609163 [Found.Phys.37:1563-1611,2007].

I found this one very helpful but am confused by his statement that "Fundamental randomness as a myth". Seems like a philosophical argument about presuppositions rather than a scientific one. If I understand Nikolic's argument he is stating that you cannot state that nature is fundamentally indeterminate because the no-hidden-variables theorems do not explicitly rule out hidden deterministic variables, they just limit the forms they can take and add some (unnamed) additional assumptions. ISTM in the absence of strong evidence for hidden deterministic variables one should draw the conclusion that nature, as represented by QM, is indeterminate with the burden of proof on the hidden variables camp

 

[jewbinson]

"In pop culture" lol

 

[DrChinese]

I found this one very helpful but am confused by his statement that "Fundamental randomness as a myth". Seems like a philosophical argument about presuppositions rather than a scientific one. If I understand Nikolic's argument he is stating that you cannot state that nature is fundamentally indeterminate because the no-hidden-variables theorems do not explicitly rule out hidden deterministic variables, they just limit the forms they can take and add some (unnamed) additional assumptions. ISTM in the absence of strong evidence for hidden deterministic variables one should draw the conclusion that nature, as represented by QM, is indeterminate with the burden of proof on the hidden variables camp

You are correct: it definitely matters where you start from in your assumptions, and Nikolic's is a nonlocal perspective. I would say that the burden is at least as much on the HV camp, and certainly cannot be on the indeterminate camp.

 

[Demystifier]

BWV and DrChinese, if we don't have a proof that something exists, does it mean that it is justified to say that it doesn't exist? Or isn't it more correct to say that it may or may not exist, but we don't know?

For example, what would you say about life on other planets? Does it exist?

In the paper BWV commented it is never stated that nature IS deterministic, but only that it COULD be deterministic in a manner compatible with the laws of QM. Many physicists think that determinism is IMPOSSIBLE due to QM, so it is important to explain that this at least is not impossible.

 

[BWV]

BWV and DrChinese, if we don't have a proof that something exists, does it mean that it is justified to say that it doesn't exist? Or isn't it more correct to say that it may or may not exist, but we don't know?

For example, what would you say about life on other planets? Does it exist?

In the paper BWV commented it is never stated that nature IS deterministic, but only that it COULD be deterministic in a manner compatible with the laws of QM. Many physicists think that determinism is IMPOSSIBLE due to QM, so it is important to explain that this at least is not impossible.

Hate to think you put me and Dr. Chinese on the same plane - I am just learning the basics of QM myself but that will not stop me from making authoritative pronouncements here ;)

The existence of life on other planets is a logical assumption from the known fact of life on our planet. It is a different leap to move from indeterminacy in QM, which is an established theory backed by a huge body of empirical research to a model of hidden deterministic variables without a body of supporting evidence. The piece claimed that indeterminacy was a "myth" of quantum mechanics when it is the logical conclusion from available science