High School Uncertain position and momentum -- A property of particles?

[rubi]

No, Bell's theorem is not and cannot be evidence against hidden variable theories such as Bohmian mechanics. It is evidence against local hidden variables, which are unlike Bohmian mechanics. One may dislike non-local hidden variables for other reasons, but there is no way to use Bell's theorem as an argument against non-local hidden variables.

Well, I did actually qualify my claim. I did say that there is no experimental evidence against hidden variables. My point is that from the point of view of Occam's razor, hidden variables should be considered (and are commonly considered) questionable, since the conspiracy involved is just too big.

Every regularity may look like a conspiracy, until you learn the mechanism that can explain the regularity.
Life is conspiracy, until you learn the theory of evolution.
Kepler laws are a conspiracy, until you learn the Newton law of gravity.
The radiation spectrum from hydrogen atom is a conspiracy, until you learn quantum mechanics.
The idea of hidden variables is a conspiracy, until you learn the laws of Bohmian mechanics.

I don't agree that the case of Bohmian mechanics is analogous to the former ones. The former ones all have testable consequences and advanced our understanding of science. We can test evolution by studying fossils. We can assure ourselves of Newton's laws by sending a sattelite to a comet and calculating its trajectory in advance. The exact same laws that lead to the hydrogen spectrum also explain the band structure of semiconductors. However, the only purpose of the equilibrium in Bohmian mechanics is to hide the conspiracy from humans.

Anyway, I don't really want to discuss interpretations again. I just find it kind of dishonest to advocate non-mainstream theories to beginners and not explain to them why they are usually disregarded by the mainstream, especially if you demand to respect from mainstream science as well (see your post #51).

 

[atyy]

Anyway, I don't really want to discuss interpretations again. I just find it kind of dishonest to advocate non-mainstream theories to beginners and not explain to them aware of why they are usually disregarded by the mainstream, especially if you demand to respect from mainstream science as well (see your post #51).

But your explanation for why they are disregarded (it is not even accepted that they are disregarded!) is wrong. In the standard interpretation, there is a Heisenberg cut. You invoke Occam's razor - but one form of Occam's razor is that there should be no Heisenberg cut since the laws of physics should apply to the whole universe.

 

[PeroK]

Indeed, admitting that some interesting questions are still not answered by science may only increase the curiosity and research spirit of young students who, one day, might become serious researchers themselves.

That's very different from where this thread started with, for example:

... So, uncertainties only exist when predicting the future, but the present existence of a particle must have definite position and momentum. Future is uncertain before it happens, but when it happens it must give an outcome.
Then, why is it said that microscopic particles posses uncertain positions and momentum?

I would suggest that the OP has avoided dealing with the awkward questions that QM poses by the get out clause "it's only one theory and not a proven fact".

I just find it kind of dishonest to advocate non-mainstream theories to beginners and not explain to them aware of why they are usually disregarded by the mainstream

Absolutely!

 

[rubi]

Essentially it's a fine tuning problem - would you consider attempts to solve fine tuning of the cosmological constant or the hierarchy problem to be conspiracy theories?

Depends on whether the solutions are just ad-hoc solutions that replace the fine-tuning by a mechanism whose only purpose is to fix the fine-tuning without any additional explanatory power apart from that or whether the solutions add something to our understanding of physics.

But your explanation for why they are disregarded (it is not even accepted that they are disregarded!) is wrong.

Well, as I argued, I don't consider it wrong, but maybe it's a matter of taste and different people are going to accept different explanations as reasonable. I certainly don't consider Valentini's solution an acceptable solution.

In the standard interpretation, there is a Heisenberg cut. You invoke Occam's razor - but one form of Occam's razor is that there should be no Heisenberg cut since the laws of physics should apply to the whole universe.

Yes, the Heisenberg cut is certainly a problem of the standard presentation of the theory and this is why I prefer presentations that incorporate modern insights, which don't suffer from this problem. For instance, consistent histories makes it pretty clear that no such cut is needed and it is just an intelligent reformulation of the standard Copenhagen point of view. (Hence, it is often referred to as "Copenhagen done right".)

 

[Prem1998]

Anyway, I don't really want to discuss interpretations again. I just find it kind of dishonest to advocate non-mainstream theories to beginners and not explain to them why they are usually disregarded by the mainstream, especially if you demand to respect from mainstream science as well (see your post #51).

As Demystefier said, admitting that some question are still not answered by science increases the curiosity of young students.
Now leave that aside. Just tell me why Bohmian mechanics isn't mainstream? Is it because it is difficult and complicated, so that it must not be true? And, what about the weird results of quantum mechanics that are simplified in Bohmian mechanics while still agreeing to the same experimental data?

 

[DrChinese]

Bell's theorem does not say that you can violate Bell inequalities by giving up hidden variables while keeping locality. And if you consider alternative proofs of Bell inequalities you can see that you actually can't escape Bell inequalities by giving up hidden variables.

I agree with rubi on this one. Bell clearly rules out either hidden variables or locality if certain QM predictions are correct. The only question is whether suitable interpretations lacking one or both can be formulated, which has nothing to do with Bell per se.

 

[DrChinese]

Just tell me why Bohmian mechanics isn't mainstream?

Beauty is in the eye of the beholder when it comes to interpretations. And many physicists don't consider choice of an interpretation important when there is no predictive difference. I am not sure there is any teaching advantage one way or the other. But I will pass along a couple of comments that may tend to answer your question.

1. Bohmian Mechanics has issues with relativity. I don't believe there is an accepted relativistic version at this time.
2. Bohmian Mechanics rejects the property of spin as being fundamental (on a par with position).
3. And the issue I have questions about: why does non-locality appear only with respect to entanglement?

I do consider Bohmian Mechanics to be a viable interpretation regardless of the above. Choice is really a personal opinion.

 

[Prem1998]

That's very different from where this thread started with, for example:I would suggest that the OP has avoided dealing with the awkward questions that QM poses by the get out clause "it's only one theory and not a proven fact".
Absolutely!

Thank you for reminding me about that. I don't think that anyone actually answered that. At the start of the thread, I was actually talking about some 'predicting the future' thing. It was about the wave function from which we can determine the probability of where the particle will be at a future instant 't'. But, unlike in the case of a die, which has uncertainties before it was thrown but it actually gives a definite outcome, then why, in this case of quantum mechanics, when the instant 't' happens, the outcome is also uncertain?

 

[vanhees71]

I don't like Bohmian mechanics, because it doesn't provide anything in addition to the minimal interpretation that's very convincing. It adds a kind of "trajectory picture" for non-relativistic particles, but the trajectories are not what's observed in particle experiments, and where they are observed (like, e.g., in terms of a trace in a cloud chamber) it's well understood within the standard minimal intepretation for decades (the first paper I know is is by N. Mott from 1929 or 1930).

 

[Prem1998]

Beauty is in the eye of the beholder when it comes to interpretations. And many physicists don't consider choice of an interpretation important when there is no predictive difference. I am not sure there is any teaching advantage one way or the other. But I will pass along a couple of comments that may tend to answer your question.

1. Bohmian Mechanics has issues with relativity. I don't believe there is an accepted relativistic version at this time.
2. Bohmian Mechanics rejects the property of spin as being fundamental (on a par with position).
3. And the issue I have questions about: why does non-locality appear only with respect to entanglement?

I do consider Bohmian Mechanics to be a viable interpretation regardless of the above. Choice is really a personal opinion.

Maybe you have some valid points against Bohimian mechanics. But what about the weird concepts that quantum mechanics introduces? Bohmian mechanics avoids them. It avoids the concept that particles don't posses definite position and momentum. Saying that particles don't have well defined position and momentum is as weird as you can get. I don't think that people even themselves understand what they're saying when they talk about such concepts of quantum mechanics. Even the inventors of quantum mechanics would have had a hard time to get something meaningful from statements like this.
So, yes, Beauty is in the eye of the beholder.

 

[Dale]

This discussion is closed due to being both philosophical and heated.