I Spooky action at a distance and various interpretations of QT

[Christian Thom]

The reason the MWI has worlds splitting on measurements is that measurements are when decoherence happens.QM does not say that decoherence happens on "the creation of particles when a symmetry would need to be broken", so no, there is no such interpretation.It's not describing any intepretation that I'm aware of.

Thank you for your answer.

 

[Christian Thom]

I am not so sure. I suspect that the action of simply passing a photon through a polarizer does not in itself constitute a measurement but that decoherence must occur as well. In other words, the measurement is only actually made when the photon is recorded by D1 or D2.

The point is absolutely crucial and it was actually to test this very point that I started this whole thread. Are you qualified in QM and have you actually calculated the result using the standard Bra-Ket rules? If not, I will, respectfully, reserve judgment until I get a reply from someone who has the appropriate skills.

I would think it depends on the polarizer : if the other polarization is absorbed, it might count as a measurement. If the other polarization is reflected, it could be used to reconstruct the original wave so it is not a measurement IMHO.

 

[PeterDonis]

I would think it depends on the polarizer : if the other polarization is absorbed, it might count as a measurement.

It does. See my post #50. My understanding is that this is the type of polarizer the OP was using.

If the other polarization is reflected, it could be used to reconstruct the original wave so it is not a measurement IMHO.

I think the more usual term for this type of device is "polarizing beam splitter".

 

[J O Linton]

I think, PeterDonis, you are being a little unfair on me. The 50 posts have already cleared up several misconceptions of mine which might have been missed if I had inroduced the modified experiment at the start.
But thank you all the same for confirming Nugatories statement that the polarizer does break the entanglement. And since you have not contradicted anything which I said in #47, I take it that what I said there is basically correct.

My reason for deferring the introduction of P3 was that, assuming that P3 did not break the entanglement, the case for some sort of SAAAD between the two photons would be quite strong. But since the entanglement is broken there is no need to consider this possibility any more.

 

[J O Linton]

In view of what you said in #53, if P3 was a polarizing beam splittier and the other polarization was allowed to go off into space - are you saying that the entanglement would remain and that the detectors would never fire together?

 

[PeterDonis]

The 50 posts have already cleared up several misconceptions of mine which might have been missed if I had inroduced the modified experiment at the start.

I'm not saying you should have introduced some "modified experiment" (not sure what you mean by this) at the start. I'm saying that, since the primary question you apparently wanted an answer to (going by the post of yours that I quoted) is "does decoherence occur immediately when a photon encounters a polarizer, or only when it encounters a detector after passing through a polarizer?", you could have just asked that question in your OP. You would have gotten an answer in one post, and you could have followed up with other questions with that primary point correctly understood at post #2 instead of post #50. I'm glad we have still cleared up some misconceptions of yours, but that could have been done with the thread started the way I describe too, since your follow-up questions would presumably still have included other things you asked about in this thread.

 

[PeterDonis]

thank you all the same for confirming Nugatories statement that the polarizer does break the entanglement.

I didn't say the polarizer breaks the entanglement. I said it causes decoherence. That's not the same thing. See my post #49 in response to @Nugatory.

 

[J O Linton]

So what is your response to #55?

 

[PeterDonis]

since you have not contradicted anything which I said in #47, I take it that what I said there is basically correct.

As far as the MWI part of post #47 is concerned, you need to rethink that in the light of my post #49.

The first partof post #47 looks correct to me as far as the calculation of probabilities is concerned, although some of your description in words is interpretation dependent.

 

[PeterDonis]

So what is your response to #55?

It has the same confusion between "breaking entanglement" and decoherence that I pointed out in post #57.

 

[J O Linton]

I admit that I am totally confused as to the difference berween 'breaking entanglement' and 'decoherence' but you haven't answered my question - if P3 is a beam splitting polarizer, will that make any difference to the behaviour of the detectors and if not, why not?

 

[PeterDonis]

if P3 was a polarizing beam splittier and the other polarization was allowed to go off into space

If the other polarization is just allowed to escape, the experiment is the same as if P3 were an ordinary polarizer that only let through the polarization that is going to encounter P1. To make any difference, the other polarization would have to have something done with it within the lab--for example, put another detector in that beam, or reflect it with a mirror so it can potentially interfere with one of the other beams.

 

[J O Linton]

I find that simply incredible. What you are saying is that you can prevent the two detectors D1 and D2 from firing together by 'doing something' with a potential beam that is going somewhere completely different.

 

[J O Linton]

since the primary question you apparently wanted an answer to (going by the post of yours that I quoted) is "does decoherence occur immediately when a photon encounters a polarizer, or only when it encounters a detector after passing through a polarizer?", you could have just asked that question in your OP. You would have gotten an answer in one post,

The trouble is - if you don't understand a topic very well, you don't know what questions to ask!

Thanks anyway.

 

[PeterDonis]

What you are saying is that you can prevent the two detectors D1 and D2 from firing together by 'doing something' with a potential beam that is going somewhere completely different.

In some runs of the experiment, yes. Suppose we put a detector D3 in the path of P3. Then on any run where D3 fires, D1 will not, so D1 and D2 can never fire together on any run where D3 fires.

On a run where D3 does not fire, the situation is the same as the case where P3 is just an ordinary polarizer and allows the photon to pass through and encounter P1. In that case, the probability of D1 and D2 firing together is what was previously calculated for that case.

 

[PeterDonis]

if you don't understand a topic very well, you don't know what questions to ask!

You apparently knew when you started this thread that "does decoherence occur immediately when a photon encounters a polarizer, or only when it encounters a detector after passing through a polarizer?" was the primary question you wanted the answer to. So you could have just asked it.

The fact that you wouldn't have known at the time that that was a "good" question to ask is beside the point, because the rule I'm suggesting that you follow is not "only ask questions that you know are good ones". It's "ask the primary question you want to know the answer to directly, instead of trying to ask it indirectly by making up a scenario that you think will lead to an answer to it". The fact that you don't understand a topic very well and so aren't sure what questions to ask is exactly why you should ask the questions you want answers to directly: because if you don't understand a topic very well, you aren't going to be very good at asking a question indirectly by making up a scenario, and a lot more time will be spent just trying to get to your actual question. In this case, about 50 posts more.

 

[PeterDonis]

I admit that I am totally confused as to the difference berween 'breaking entanglement' and 'decoherence'

"Breaking entanglement" is interpretation dependent. For example, if P3 absorbs a photon, that "breaks entanglement" in a collapse interpretation, but not in the MWI.

Decoherence, however, is not interpretation dependent. The two alternatives "P3 absorbs the photon" and "P3 passes the photon" are decoherent in any interpretation.

 

[Christian Thom]

The reason the MWI has worlds splitting on measurements is that measurements are when decoherence happens.QM does not say that decoherence happens on "the creation of particles when a symmetry would need to be broken", so no, there is no such interpretation.It's not describing any intepretation that I'm aware of.

After some search and the viewing of a very good recent video from S. Hossenfelder, I think it is close to the super-determinism, as it exploits the same loophole of Bell's theorem : the statistical independence.

 

[PeterDonis]

a very good recent video from S. Hossenfelder, I think it is close to the super-determinism

That's pretty much the viewpoint Hossenfelder seems to hold, yes.

 

[Jarvis323]

After some search and the viewing of a very good recent video from S. Hossenfelder, I think it is close to the super-determinism, as it exploits the same loophole of Bell's theorem : the statistical independence.

I'm not sure what to think about her video. She sort of ignored issue that most people I've seen have presented as the deal breaker in favoring super-determinism. According to others, in order for super-determinism to be plausible, the past or initial conditions of the universe would have to be very very "special", so as to be in just the right way that we happen to see the correlations we do. I'm careful not to validate these concerns, because I haven't studied it closely enough. I may be one of the people she talks about who doesn't know what they're talking about.

There is apparently a similar issue with MWI, in that in some of the less common world lines, people will observe universes that look highly "special", in various weird ways, or look like some seriously spooky action at a distance was happening.

Sabine is hoping that in the future, large scale data analysis, using AI, and experiments of events in the non-chaotic regime, will make it look obvious that our reality is super-deterministic. But if that happens, couldn't we also just be equally a very very special world in a MWI reality at that point?

A truly randomly generated number will have equally likely outcomes, each time a new one is generated. Suppose a uniform random number generator generates numbers between 1 and 10^100^100^100. It's theoretically possible that you could generate the same number 10^100 times in a row, or even indefinitely. In fact that result is just as likely as any other sequences of numbers. It's just not typical in the sense that most possible sequences will look more "random" (or more typical).

In fact, we don't need MWI, or super-determinism, or entanglement at all right? We can just have true randomness, and be really really lucky? In any case all of these possibilities (being really lucky rolling the dice, a very very special and precisely and elaborately arranged domino arrangement, or we're a special highly atypical world in a MWI universe) seem unappealing for similar reasons. We usually rely on the assumption that if QM is giving us randomness, it will look like "randomness", rather than we just might get super lucky. Or we assume that even if MWI is correct, that the world line we've experienced thus far is fairly typical.

This said, maybe the "fine tuning" problem in QM foundations isn't what people make it out to be. Maybe the narrowest sense in which the independence needs to be violated need not be "
"special" in the sense people make out it be?

 

[gentzen]

I'm not sure what to think about her video.

Her video is disappointing in various ways. For example, she cheery picks quotes from Nicolas Gisin, Anton Zeilinger, and Tim Maudlin, (and also from a paper by Shimony, Horne, and Clauser) only to conclude:

As you can see, we have no shortage of men who have strong opinions about things they know very little about, but not like this is news.

She ends her video saying:

Call me crazy if you want but to me it’s obvious that superdeterminism is the correct explanation for our observations. I just hope I’ll live long enough to see that all those men who said otherwise will be really embarrassed.

Before the end she repeats an important point she already made in 2011:

But if you want to find out whether measurement outcomes are actually determined, you have to get out of the chaotic regime. This means looking at small systems at low temperatures and measurements in a short sequence, ideally on the same particle. ... And this makes me think that at some point it’ll just become obvious that measurement outcomes are actually much more predictable than quantum mechanics says. Indeed, maybe someone already has the data, they just haven’t analyzed it the right way.

She also hints at an important point about how violation of "statistical independence" actually plays out:

Well, that’s entirely unsurprising. If you considered measuring something but eventually didn’t, that’s just irrelevant. The only relevant thing is what you actually measure. The path of the particle has to be consistent with that.

But I find this too little, and not well explained. From my perspective, this would have been the place to explain the impression that the initial state is "fine tune", and why this is not a problem.

Another huge disappointment for me was that some of the arguments got dropped completely, arguments where I was never sure whether it was Tim Palmer who contributed them. For example, I noticed before that Palmer put more stress on the importance of the similarity between von Neumann equation and Liouville equation and the relation to the linearity of QM. There was a seminar where both mentioned it (Hossenfelder at 13:24 and Palmer at 46:21), and Palmer excusing himself for repeating Sabine, "but I want to again stress..." hinted that for him, this was not just something "obvious", but something deep and imporant.

 

[Jarvis323]

But I find this too little, and not well explained. From my perspective, this would have been the place to explain the impression that the initial state is "fine tune", and why this is not a problem.

The position she takes I think is that any implications one might draw about how the correlations were constructed is speculative and irrelevant. All that matters is that the correlations existed.

She is right that the fine tuning argument presupposes a fictional space of possible parameters, and there is no concrete way to assign a meaningful probability (e.g. that things exist as they do, rather than some other hypothetical way) using such a fictional space.

Ultimately it seems to me that she is saying that we should just assume that the correlations exist somehow, and then just calculate.

 

[Morbert]

Ultimately it seems to me that she is saying that we should just assume that the correlations exist somehow, and then just calculate.

This seems like a peculiar prescription on her part, considering we can just calculate even without assuming correlated hidden variables. She's presenting a just so story, but she needs to sell it too.

 

[J O Linton]

I wonder if I could respectfully redirect your attention back to the OP? The original question was: in the context of the experiment described in #1, how would adherents of the standard interpretation, the MWI, the Pilot wave interpretation and, we may now add, superdeterminism respond to the charge that their interpretation involved 'spooky action at a distance (whatever Einstein meant by that)?

 

[Lord Jestocost]

Adherents of the standard interpretation wouldn't see any reason to respond to the charge that their interpretation involved ‘spooky action at a distance’. Here is a fundamental error in thinking. The world is not classical, and ideas as ‘non-locality’ or ‘spooky action at a distance’ are not needed because the world is quantum mechanical. Murray Gell-Mann puts it in “The Quark and the Jaguar” (chapter: “Quantum Mechanics and flapdoodle”) in the following way:

“The label ‘nonlocal’ applied by some physicists to quantum-mechanical phenomena like the EPRB effect is thus an abuse of language. What they mean is that if interpreted classically in terms of hidden variables, the result would indicate nonlocality, but of course such a classical interpretation is wrong.” [bold by LJ]

One should thus avoid the term ‘quantum non-locality’ and not mix it up with ‘quantum non-separability’, which is indeed rooted in the way the quantum formalism represents systems and sub-systems.

 

[J O Linton]

In a letter to Born Einstein objected to the standard (statistical) interpretation with the words: " I cannot seriously believe in it because the theory cannot be reconciled with the idea that physics should represent a reality in time and space, free from spooky action at a distance" so he obviously thought that the interpretation required SAAAD. I agree, however, that the 'shut up and calculate' brigade would simply ignore the charge. But simply ignoring the charge doesn't make it go away. On any reasonably realistic interpretation, when photon A arrives at P1 and the wavefunction collapses, the subsequent behaviour of photon B is irrevocably altered. How is that not SAAAD?

Since SAAAD (if it happens at all) only occurs during the 'collapse of the wave function' I think we can take it that adherents of MWI would refute the charge on the basis that decoherence simply decrees that after A has encountered P1, the multitude of possibilities that existed in a superposition of states has now simply reduced to two possibilities, both of which are realized. Would you agree?

 

[gentzen]

She is right that the fine tuning argument presupposes a fictional space of possible parameters, and there is no concrete way to assign a meaningful probability (e.g. that things exist as they do, rather than some other hypothetical way) using such a fictional space.

She is right on the one hand, but she also undercuts her own explanation by saying: "Superdeterminism is exactly as deterministic as plain old vanilla determinism." There is a difference between determinism and superdeterminism, and denying that difference is not helpful.

This seems like a peculiar prescription on her part, considering we can just calculate even without assuming correlated hidden variables. She's presenting a just so story, but she needs to sell it too.

Exactly, she needs to sell it.

I wonder if I could respectfully redirect your attention back to the OP?

Good point. I am not especially keen on discussing superdeterminism anyway, since I learned already that it is very easy to get myself into an uncomfortable position.

 

[PeterDonis]

after A has encountered P1, the multitude of possibilities that existed in a superposition of states

What do you mean by "the multitude of possibilities that existed in a superposition of states" here?

 

[PeterDonis]

What do you mean by "the multitude of possibilities that existed in a superposition of states" here?

@J O Linton if what you mean is this from the OP...

When the two photons leave the source they are in a superposition of an infinite number of states with their polarisation planes in all possible directions (but always at right angles to each other)

...then your description is incorrect. The initial entangled two-photon state is not a superposition of an infinite number of states. It's just one state. The different possible polarization planes are different ways we can describe the one state the photon is in, but those are just different descriptions. The only polarization directions that are physically meaningful are the ones we actually choose to measure with polarizers.

 

[J O Linton]

I think I see what you mean. What you are saying is that, unlike a true superposition of states which we could interrogate to find out which state the system collapses into, we cannot ask the photon, 'what is your angle of polarisation?' - all we can do is ask 'are you vertical?', or whatever.

So what is the best language to use to describe the state of polarization of the entangled photons immediately after they have left the source?

 

[PeterDonis]

unlike a true superposition of states

There is no such thing as "a true superposition of states". Superposition is always basis dependent; we can always find a basis in which the given state is one of the basis states.

which we could interrogate to find out which state the system collapses into

There is never any way to ask any photon "which direction are you polarized in" where the answer could be any direction whatever. For any photon, all you can do is pick a direction for your polarizer and see if the photon passes through or not.

what is the best language to use to describe the state of polarization of the entangled photons immediately after they have left the source?

An entangled state of two photons with total spin zero.

 

[DrChinese]

One should thus avoid the term ‘quantum non-locality’ and not mix it up with ‘quantum non-separability’, which is indeed rooted in the way the quantum formalism represents systems and sub-systems.

Or you could just say that "quantum non-locality" is the correct term to describe the set of phenomena that is observed in line with the predictions of QM. Note that this is an umbrella for not only apparent non-locality, and apparent "quantum non-separability", but also what might be called "quantum non-temporal" (there is no widely accepted term for this). An entangled system of 2 particles (say photons) does not require that they ever overlapped in any region of spacetime (they were always separated), and in fact need not have ever co-existed (ergo the "non-temporal" entanglement).

The rationale for using the phrase "quantum non-locality" is that it is already in widespread use to include the umbrella of observed entangled phenomena.