I How can Bohmian mechanics explain entanglement?

[berkeman]

Thread closed temporarily for review by the Mentors.

Two threads with very similar subjects have been merged now. This thread is now open provisionally.

 

[DrChinese]

Can someone please explain whether the experimental scenarios in the paper have actually been performed? They outline a specific scenario and a specific inequality. Is the experiment is performed and the inequality is broken, then we can safely rule out all finite speed causal influence models even if they’re faster than light.

To anyone who has read the paper, have these experiments been done? If not, is it still feasible for the results to be explained by finite speed causal influence models?

Experimental tests of Bohmian Mechanics (BM or dBB) - as well as theoretical models - have been performed/analyzed. Fairly regularly they contradict standard QM (i.e. the Bohmian view is always rejected). But here's a shocker: none of these are accepted (for one reason or another) by the BM community. See for example:

A first experimental test of de Broglie-Bohm theory against standard quantum mechanics (2002)

So you must take these with a grain of salt, regardless of your viewpoint.

 

[sahashmi]

Experimental tests of Bohmian Mechanics (BM or dBB) - as well as theoretical models - have been performed/analyzed. Fairly regularly they contradict standard QM (i.e. the Bohmian view is always rejected). But here's a shocker: none of these are accepted (for one reason or another) by the BM community. See for example:

A first experimental test of de Broglie-Bohm theory against standard quantum mechanics (2002)

So you must take these with a grain of salt, regardless of your viewpoint.

I’m not talking about an experimental test of BM. Please read the paper I linked. They are talking about an experiment to rule out all finite speed causal influence models that would explain entanglement, even if they’re superluminal. They derive an inequality which must be broken given the particular experimental scenario they outline. Has this experiment been done?

 

[DrChinese]

I’m not talking about an experimental test of BM. Please read the paper I linked. They are talking about an experiment to rule out all finite speed causal influence models that would explain entanglement, even if they’re superluminal. They derive an inequality which must be broken given the particular experimental scenario they outline. Has this experiment been done?

This same team (Gisin et al) works around all the various FTL models, including BM. There are so many variants, all I can say is that is that you won't really see most theoretical treatments accompanied by a related experiment. As you already know, variants with FTL<10,000c are already ruled out experimentally. Generally, variants with an absolute reference frame have been ruled out in various manners. But again, most of these type arguments are rejected by supporters anyway.

So... specifically ruling out [10,000c<FTL<infinity] models is not a particularly hot topic. Quantum nonlocality - well-accepted in science today - does not really have a "speed" - infinite or otherwise. Delayed choice experiments make a mockery of there being a speed that can be calculated. Such experiments fit with garden QM with no additional assumptions required. However, there is no explanatory mechanism behind the usual QM.

 

[sahashmi]

This same team (Gisin et al) works around all the various FTL models, including BM. There are so many variants, all I can say is that is that you won't really see most theoretical treatments accompanied by a related experiment. As you already know, variants with FTL<10,000c are already ruled out experimentally. Generally, variants with an absolute reference frame have been ruled out in various manners. But again, most of these type arguments are rejected by supporters anyway.

So... specifically ruling out [10,000c<FTL<infinity] models is not a particularly hot topic. Quantum nonlocality - well-accepted in science today - does not really have a "speed" - infinite or otherwise. Delayed choice experiments make a mockery of there being a speed that can be calculated. Such experiments fit with garden QM with no additional assumptions required. However, there is no explanatory mechanism behind the usual QM.

So just to be clear, models where there is a causal influence that has a finite speed from one measurement choice to another faster than 10,000 x speed of light have not been experimentally ruled out, correct?

Secondly, did you read the paper I linked?

I’ll be honest. I don’t think it’s possible for the correlations to occur without a cause. First, this contradicts the history of all scientific inquiry. Secondly, if everything is local, a two pair bell experiment means the particles are essentially behaving like independent coins. But why would the coins be correlated to each other unless a) they are locally predetermined to result in the same outcomes (ruled out by Bell’s theorem) or b) they’re influencing each other? What third option is there? The third option seems conspiratorial and at that point, you might as well believe in superdeterminism.

If two coins are independent, the probability of them landing on the same side is infinitesimally low. Saying that they are correlated because they follow some law is not saying much. It’s the same as saying “the correlation happens because the correlation happens non locally”.

 

[pines-demon]

Secondly, did you read the paper I linked?

Do you agree that the paper says that Bohmian mechanics is not concerned by that paper?

 

[sahashmi]

Do you agree that the paper says that Bohmian mechanics is not concerned by that paper?

Yes I do, but I’m still interested in knowing whether the experiments proposed in the paper have been done. They propose experiments to rule out finite speed influence models where the speed is faster than light

 

[pines-demon]

Yes I do, but I’m still interested in knowing whether the experiments proposed in the paper have been done. They propose experiments to rule out finite speed influence models where the speed is faster than light

If these experiments would have been done, wouldn't the author cite them?

 

[sahashmi]

If these experiments would have been done, wouldn't the author cite them?

The author’s paper is more than a decade old

 

[Nugatory]

I’ll be honest. I don’t think it’s possible for the correlations to occur without a cause.

Yes, but in your posts here you are making a much stronger statement: that the causal influence starts at one measurement and (in a way that cannot be reconciled with relativity) causes an effect at the spacelike-separated other measurement.

 

[PeterDonis]

If two coins are independent, the probability of them landing on the same side is infinitesimally low.

Um, no, it's 1/2. Four possibilities: HH, HT, TH, TT. Two of them have both coins on the same side.

 

[sahashmi]

Um, no, it's 1/2. Four possibilities: HH, HT, TH, TT. Two of them have both coins on the same side.

I’m assuming over many tosses of course

 

[PeterDonis]

I’m assuming over many tosses of course

Then I have no idea what you are talking about. "The coins landing on the same side" makes sense if you toss each coin once. If you toss each coin many times, I don't know what it means. You need to be more specific about what you are describing.

 

[sahashmi]

Then I have no idea what you are talking about. "The coins landing on the same side" makes sense if you toss each coin once. If you toss each coin many times, I don't know what it means. You need to be more specific about what you are describing.

Entangled particle measurements are no different from stochastic coins always ending up tossing to the same side.

If you had two coins landing on the same side every time, you would reasonably assume one of three things:

a) they’re each locally predetermined to land on the same side

b) the coins are always communicating making sure they’re in sync, but before either one is measured

C) after one lands, the coin somehow communicates to the other to land on the same side.

A) has been ruled out by Bell’s theorem. Note that any sort of communication mid flight even though this would be non local cannot explain the results either (since any sort of predetermined state before measurement doesn’t work)

This leaves c).

People who “deny realism” and pretending like that explains the correlations are ultimately just putting their head under the sand and pretending like there’s another option. There isn’t. This is why John Bell was annoyed at people misunderstanding his theorem.

You cannot escape non locality. Perhaps this non locality is coming from finite speed but superluminal influences. These have not been ruled out as far as I’m aware.

 

[PeroK]

Entangled particle measurements are no different from stochastic coins always ending up tossing to the same side.

John Bell proved otherwise. The critical difference is that electron spin can be measured about different axes. This entails a much richer set of possible experiments.

 

[PeroK]

People who “deny realism” and pretending like that explains the correlations are ultimately just putting their head under the sand and pretending like there’s another option. There isn’t. This is why John Bell was annoyed at people misunderstanding his theorem.

An additional problem is what you consider one photon or electron commicates to the other? If you studied these experiments thoroughly you would see that there is no simple message that could be conveyed.

It may be the case that in a simplistic presentation of these experiments it appears plausible that a photon could communicate some simple information like "we've been detected and I chose this variable". But, in fact, the spin or polarisation is rather inferred from an absorption event. All the photon or electron could really communicate is something like " I've just been absorbed into some sort of detection device".

Even before Bell, Bohr and other leading physicists had decided what QM was telling them was right. In your opinion, their heads must gave been even further in the sand than ours today! One reason is that even without the evidence subsequent to Bell's theorem, the hidden variables or FTL signalling were physicaly implausible - even if not theoretically ruled out.

IMO, even before Bell, you are in very difficult waters trying to impose classical realism on QM experiments.

 

[PeroK]

PS my opinion is that if the electron behaves realistically then we must be able to detect its axis of rotation. Which, of course, we cannot. Modern QM by JJ Sakurai begins with simple experiments on electron spin and photon polarisation, and concludes immediately that we need a new mathematical model to explain this behaviour.

The problem with EPR is that they didn't have to propose any actual mechanism to explain experimental phenomena. They simply tried to undermine QM without providing any alternative.

A powerful reason that physicists have stuck with QM and QFT is that ultimately they do everything a physical theory must do. No more and no less. Whereas, the alternative is precisely nothing. Only the vague conclusion that QM and relativity are incompatible and there is no modern particle physics.

 

[sahashmi]

John Bell proved otherwise. The critical difference is that electron spin can be measured about different axes. This entails a much richer set of possible experiments.

I obviously meant they can be viewed like that on the same axes. Change the coin analogy to flipping stochastic coins on either your left or right hand and the same problem remains.

An additional problem is what you consider one photon or electron commicates to the other? If you studied these experiments thoroughly you would see that there is no simple message that could be conveyed.

It may be the case that in a simplistic presentation of these experiments it appears plausible that a photon could communicate some simple information like "we've been detected and I chose this variable". But, in fact, the spin or polarisation is rather inferred from an absorption event. All the photon or electron could really communicate is something like " I've just been absorbed into some sort of detection device".

Even before Bell, Bohr and other leading physicists had decided what QM was telling them was right. In your opinion, their heads must gave been even further in the sand than ours today! One reason is that even without the evidence subsequent to Bell's theorem, the hidden variables or FTL signalling were physicaly implausible - even if not theoretically ruled out.

IMO, even before Bell, you are in very difficult waters trying to impose classical realism on QM experiments.

The absorption event could easily be part of a hidden variable that determines the spin, and so the spin can indirectly be communicated to the other particle, likely through means we can’t detect yet. This has NOT been ruled out since the notion of the impossibility of superluminal communication comes from us not being able to predict the spins in advance, NOT something in principle.

It is perfectly tenable, even if not proven yet, for each particle to have local hidden variables and yet as soon as one of them is measured, a superluminal signal being sent to influence the other particle. It would result in the same empirical observations in QM.

PS my opinion is that if the electron behaves realistically then we must be able to detect its axis of rotation. Which, of course, we cannot. Modern QM by JJ Sakurai begins with simple experiments on electron spin and photon polarisation, and concludes immediately that we need a new mathematical model to explain this behaviour.

The problem with EPR is that they didn't have to propose any actual mechanism to explain experimental phenomena. They simply tried to undermine QM without providing any alternative.

A powerful reason that physicists have stuck with QM and QFT is that ultimately they do everything a physical theory must do. No more and no less. Whereas, the alternative is precisely nothing. Only the vague conclusion that QM and relativity are incompatible and there is no modern particle physics.

This is incorrect. Why are you assuming that we must be able to determine something if it’s all realistic? You don’t get to decide what things “must” do. Reality doesn’t care about opinion. And no, current QM doesn’t do everything a physical theory should do: it doesn’t give us a complete picture of what’s going on. Heck, even practically, it doesn’t give us full predictions. It only gives probabilistic predictions

 

[Nugatory]

And no, current QM doesn’t do everything a physical theory should do: it doesn’t give us a complete picture of what’s going on.

Ahh…. No physical theory does that. Consider even something as solid as Newtonian gravity: dig into it a little bit, ask why there should be an attractive force between masses and what is really going on to pull two masses towards one another and you’ll find that there is no answer. Appealing to GR doesn’t make the problem go away, it just leaves us wondering what is going on that causes stress-energy to curve spacetime, and for matter what is this spacetime that is curving.
The lack of a “complete picture” bothers most people more when it comes to QM, but if probe the objections you will find that the theory isn’t more deficient than others, but rather that it is much harder to reconcile with our intuition about how things “ought” to work.

 

[javisot]

And no, current QM doesn’t do everything a physical theory should do: it doesn’t give us a complete picture of what’s going on. Heck, even practically, it doesn’t give us full predictions. It only gives probabilistic predictions

QM tells us (almost) everything that can be said about QM, that is, about the quantum regime. If you want QM to do more than that, the problem is yours.

 

[Nugatory]

It is perfectly tenable, even if not proven yet, for each particle to have local hidden variables and yet as soon as one of them is measured, a superluminal signal being sent to influence the other particle. It would result in the same empirical observations in QM.

It is perfectly tenable - if you are willing to give up relativity. That is a very heavy lift, only marginally less heavy than “Perpetual motion is perfectly tenable, if we give up thermodynamics”.

It is possible to keep relativity and Bell’s theorem, just not in a way that satisfies your sense of how the world ought to work.

 

[sahashmi]

Ahh…. No physical theory does that. Consider even something as solid as Newtonian gravity: dig into it a little bit, ask why there should be an attractive force between masses and what is really going on to pull two masses towards one another and you’ll find that there is no answer. Appealing to GR doesn’t make the problem go away, it just leaves us wondering what is going on that causes stress-energy to curve spacetime, and for matter what is this spacetime that is curving.
The lack of a “complete picture” bothers most people more when it comes to QM, but if probe the objections you will find that the theory isn’t more deficient than others, but rather that it is much harder to reconcile with our intuition about how things “ought” to work.

Gravity is propagated through gravitational fields which are much more easily imagined and the theory of GR is much more “complete” than quantum mechanics. There’s a reason the second is initially perceived as more weird and it’s not because of faulty intuitions.

Quantum mechanics posits non local correlations without any influences at all. It’s arguably a form of “action at a distance” like the original Newtonian gravity. Of course, that ended up being wrong and proven to be incorrect. The same will probably happen with QM

 

[sahashmi]

QM tells us (almost) everything that can be said about QM, that is, about the quantum regime. If you want QM to do more than that, the problem is yours.

Physical theories are designed to give us clues about reality and help us understand what’s going on and how to connect perceived measurable outcomes to things happening in the world when we’re not measuring. Your argument is effectively circular and no different from gibberish. A theory about goblins tells me everything about the goblin regime too.

 

[sahashmi]

It is perfectly tenable - if you are willing to give up relativity. That is a very heavy lift, only marginally less heavy than “Perpetual motion is perfectly tenable, if we give up thermodynamics”.

It is possible to keep relativity and Bell’s theorem, just not in a way that satisfies your sense of how the world ought to work.

It is easy to give up relativity once you realize that you cannot explain the non local correlations without giving it up. Any kind of superluminal causation requires a preferred reference frame and people like maudlin, and bell, people who’ve put more thought into this than 99% of physicists, think that some form of non local causation is inescapable.

If you keep relativity, there is no reason for why one particle should be correlated to another at a distance. Appealing to an abstract mathematical equation doesn’t actually explain anything. It’s just a description. I can write an equation down describing how two coins land on the same side every time, but this does not tell me why or how they do. The same applies to quantum correlations. There is a reason why eminent scientists like Einstein and Bell thought this doesn’t make sense, and yet somehow, so many physicists are arrogant enough to think that they were just “thinking about it the wrong way.” Any time someone says anything nonsensical, they can resort to the same kind of argument you just made: “you just have to think about this differently. Your intuitions are mistaken.”

This attitude by physicists reminds me of god believers. “You just don’t understand god. He exists outside of space and time and yet magically still affects the physical world. Don’t ask further questions please.”

 

[Sambuco]

It is perfectly tenable, even if not proven yet, for each particle to have local hidden variables and yet as soon as one of them is measured, a superluminal signal being sent to influence the other particle. It would result in the same empirical observations in QM.

If we try to mantain the notion of causation, the question arises about what is the cause and what is the effect, which becomes observer-dependent. There are other hints to reject the notion of fundamental causation, such as the time symmetry of fundamental physical laws (https://quantum-journal.org/papers/q-2021-08-09-520/).

And no, current QM doesn’t do everything a physical theory should do: it doesn’t give us a complete picture of what’s going on.

There exists a possibility that everything that happens is exactly what QM predicts: the appearance of certain correlated discrete events at spacetime points without a "cause". Some information-based interpretations favored this position, such as Rovelli's relational quantum mechanics (https://link.springer.com/article/10.1007/BF02302261). It's difficult to accept this view without good justification, which is why many people are working on what is known as the quantum reconstruction program, attempting to derive the entire mathematical apparatus of QM from a few well-motivated physical principles.

Lucas.

 

[PeterDonis]

Entangled particle measurements are no different from stochastic coins always ending up tossing to the same side.

Yes, they are. The latter cannot violate the Bell inequalities. The former can.

 

[PeterDonis]

Thread closed for moderation.

 

[Nugatory]

The thread will stay closed