Question about an entanglement paper

[kurt101]

Oops, yes, it was a typo, I meant "does not violate QFT". I have fixed the original post.

The interpretation of non-local action that I am using as applied to the Alain Aspect 1983 experiment is that measuring one of the entangled photons affects the other. For this interpretation, statistically the order does not matter and for all practical purposes you would not be able to detect this order. To the best of my knowledge QFT applies to the practical things we can actually measure. So based on the test you outlined, I would not rule out this non-local interpretation of the Aspect experiment as a possibility.

Both. QFT requires field operators at spacelike separated events to commute. That means single pairs must commute, and it also implies that the statistical results will be independent of ordering.

Single pairs must commute for the math to work out, but I am thinking that this is different than the actual mechanism having to commute. If the actual mechanism does not commute, but the state it acts upon is random, you would get the same statistical result.

 

[PeterDonis]

Single pairs must commute for the math to work out, but I am thinking that this is different than the actual mechanism having to commute.

In QFT, the field operators are the "actual mechanism".

 

[PeterDonis]

The interpretation of non-local action that I am using

Are you trying to describe the interpretation used in the paper described in the OP? Or is this an interpretation that appears in some other reference? Or is it just something you made up?

 

[PAllen]

I think the order matters to the interpretation because it preserves causality, but unless you can some how predict the state of the entangled particle before measuring it, I don't see how you could use this knowledge to send a message FTL.

If the order matters, you have causality outside of the light cone. It is precisely the commuting property that guarantees there is no ftl causality, because you can’t distinguish whether A caused B or B caused A.

 

[Dale]

I think the order matters

The order can’t matter because the order is not the same in all frames.

 

[Buzz Bloom]

They would not remain synchronized with the central clock except momentarily.

Hi Dale:

I think I may be understanding this. Each carriage experiences a radial acceleration away from the center. This acceleration changes the relative time rate in each carriage as, compared with the time rate at the center. Is this correct? Is it also correct that the the rate of time is the same in all of the carriages? If I am correct about these guesses, I would appreiate seeing an equation that compares the rate of time differences between the carriages and the center point in terems of the accelleation and/or the radius and the tangential velocity. I tried (and failed) to find this by an online search, was probably chose the search keys badly.

Regards,
Buzz

 

[Ibix]

This acceleration changes the relative time rate in each carriage as, compared with the time rate at the center. Is this correct?

No. It's just that the circling clocks are moving at constant speed $v$ compared to the central clock, so have the usual time dilation factor of $1/\sqrt{1-v^2/c^2}$. GPS satellite clocks tick at a very slightly modified rate to account for a (slightly more complex because of gravity) version of this.

 

[kurt101]

Are you trying to describe the interpretation used in the paper described in the OP? Or is this an interpretation that appears in some other reference? Or is it just something you made up?

No, nothing from the paper, but what I thought Bell meant by non-local action as applied to an actual experiment.

 

[PeterDonis]

what I thought Bell meant by non-local action as applied to an actual experiment.

Please give a reference for whatever Bell paper you are basing this on.

 

[kurt101]

The order can’t matter because the order is not the same in all frames.

If the order matters, you have causality outside of the light cone. It is precisely the commuting property that guarantees there is no ftl causality, because you can’t distinguish whether A caused B or B caused A.

The order matters to the *interpretation* of non-local action; the interpretation is not something we can directly measure, but only something we can infer from statistics and the experiments.

With the non-local action interpretation there is no way to directly distinguish whether A caused B or B caused A and so your comment about causality outside of the light cone does not apply.

Take the EPR experiment done by Alain Aspect in 1983. Call the entangled photons A and B. You can only measure either A or B first. Say you decide to always measure A first. At the end of the experiment, after many iterations, you still get the correlation that A's polarizer had an effect on B. You get that correlation even if you change the orientation of A's polarizer so it changes faster than any signal that could be transmitted at the speed of light. You can also say that B's polarizer had an effect on A, but this would violate causality, because you measured B after you measured A. You might say there were some observers that did not see it that way, and to that comment I would say steer B back around to where A was measured by using gravity, so that there is no question to any observer that B was measured second.

So if you are in the non-local action camp and subscribe to causality, based on this experiment it would be logical to conclude that there is a definite order even though you can not directly observe it.

 

[PeterDonis]

The order matters to the *interpretation* of non-local action

This seems to contradict:

With the non-local action interpretation there is no way to directly distinguish whether A caused B or B caused A

"No way to directly distinguish whether A caused B or B caused A" sounds like "order doesn't matter".

You can only measure either A or B first.

No, you set up the measurements to be spacelike separated so there is no frame-independent fact of the matter about which one you measure first.

Say you decide to always measure A first.

As the experiment was set up, there was no attempt to control the exact measurement times in this way. The only thing that was controlled was that the measurements were spacelike separated (meaning that the time windows for the measurements had to be small compared to the light travel time over the path lengths involved).

So I assume you are proposing an alternate version of the experiment, where the ordering in some particular chosen frame (the "lab" frame) is controlled explicitly?

f you are in the non-local action camp and subscribe to causality, based on this experiment it would be logical to conclude that there is a definite order even though you can not directly observe it.

I don't see how, since you could just as easily do the experiment enforcing the opposite order, and the results would be indistinguishable. In other words, experimentally the order doesn't matter. And relativity explains why: because the order is not invariant, and only invariants can affect the actual physics.

 

[kurt101]

Please give a reference for whatever Bell paper you are basing this on.

Bell's paper Bertlemann's socks: https://hal.archives-ouvertes.fr/jpa-00220688/document
The third explanation:

Thirdly, it may be that we have to admit that causal influences
- do go faster than light. The role of Lorentz invariance in the completed theory would then be very problematic. An "ether" would be the cheapest solution /22/. But the unobservability of this ether would be disturbing. So would the impossibility of "messages' faster than light,
which follows from ordinary relativistic quantum mechanics in so far as
it is unambiguous and adequate for procedures we can actually perform.
The exact elucidation of concepts like 'message' and 'we' would be a
formidable challenge.

 

[kurt101]

So I assume you are proposing an alternate version of the experiment, where the ordering in some particular chosen frame (the "lab" frame) is controlled explicitly?

Yes, it is a slightly modified version of the experiment.

I don't see how, since you could just as easily do the experiment enforcing the opposite order, and the results would be indistinguishable. In other words, experimentally the order doesn't matter. And relativity explains why: because the order is not invariant, and only invariants can affect the actual physics.

Exactly, the results would be indistinguishable! This is what I have been saying all along and is why I call it an interpretation.

 

[Dale]

The order matters to the *interpretation* of non-local action

I am OK with that. The interpretation can change from frame to frame.

the interpretation is not something we can directly measure, but only something we can infer from statistics and the experiments

Not really. Interpretations are simply assumed for convenience, aesthetics, philosophical, or personal reasons. I am not really interested in interpretations.

 

[PeterDonis]

the results would be indistinguishable! This is what I have been saying all along and is why I call it an interpretation

I don't see the point of an interpretation that tries to distinguish indistinguishable results.

Bell's paper Bertlemann's socks: https://hal.archives-ouvertes.fr/jpa-00220688/document
The third explanation:

This explanation does not say that spacelike separated events that are causally connected have to have a definite order. It just says that spacelike separated events can be causally connected. Note that the word "order" appears nowhere in Bell's description of this interpretation.

Bell does propose an "ether" (which would seem to suggest some sort of preferred frame and therefore a preferred simultaneity convention) as one possible way of implementing this solution, but it's not the only possible one (and Bell does not claim it is--he only says ether would be the "cheapest" solution). Another would simply be to develop a concept of "causality" that did not require one to distinguish between the "cause" and "effect", at least not in the sense that one has to come before the other. Which is still a challenge, but as Bell says, any explanation you pick is going to be a challenge.

 

[kurt101]

Interpretations are simply assumed for convenience, aesthetics, philosophical, or personal reasons. I am not really interested in interpretations.

I am interested in interpretations because I want to see what the machinery of the universe looks like. I think it is important to discuss interpretations that show promise to advance our understanding. My motivation for my question in this thread was to understand if there was a real challenge to the non-local causal interpretation. I think the challenge that PeterDonis brought up about field operators in QFT having to commute is a good challenge to this and something I plan to learn more about.
[Edit: that is field operators of space like separated events commute]

 

[Dale]

I am interested in interpretations because I want to see what the machinery of the universe looks like.

That sounds completely counter productive. If you want to see what the machinery looks like then study the math. The interpretations are just bedtime stories that we tell each other.

 

[DarMM]

Can you explain why non-local interaction means relativity is wrong?

Checked my emails and saw this. Just to say I've left the forums so I won't be replying beyond this, but it felt wrong to leave you hanging. I didn't go into much detail as this is a Relativity forum, so wasn't sure how much detail on QM to give.

Wood and Spekkens in a 2013 paper (https://arxiv.org/abs/1208.4119) showed that nonlocal interactions have to be fine-tuned to replicate QM. This fine tuning (unless you believe in preposterously specific conditions in the early universe) has to come about via thermalisation in the early universe. Out of this equilibrium state you'd have observable violations of Relativity.

So if the nonlocal interpretations are right there are regimes where Relativity is violated. This is nothing to do with commutation at spacelike intervals.