A Bell Theorem with no locality assumption?

nikman

The most illuminating Zeilinger paper IMO is one he did back in 2005 with Brukner. "Quantum Physics as a Science of Information". SpringerLink sits on it unless you want to give them money. But fortunately the gods have smiled it's available in toto via Google books:

http://tinyurl.com/2aoydkx

Leggett-Garg incorporates a nonlocality assumption and tests for "realism" (counterfactual definiteness, whatever). Inferentially or by default that's what Tresser also does. Or not? Anyway, how are they different?

Gisin indeed has become awfully hard to follow. He's hiking deep into the woods. As I read him (and this interpretation of mine may very well be of absolutely no value whatsoever) it's all somehow coming back to the measurement problem. Hopefully what he's up to will become clear in time.

charlylebeaugosse

With Leggett this paper shares the essential point that it is realsim and not locality that is the false asumption in Bell's theory. The author hope to soon write down "proofs" of that in terms of new experiments proposals and a discussion on the basis of the old superposition principle. One tool will be revisiting the Welcher Weg discussion, with views that are not new to Dirac, but new to Einstein, Bohr, Wheeler, Feyman, and many others, including Zeilinger whose views on locality are not fully clear, are they?

As for Gisin, he loves to explain why he is smarter than Einstein and is smart enough indeed to know that the paper that HE points out as THE start of the fashion for Bell theorem in PRL is a fraud.
Like many other localists, he cannot be (also) stupid enough despite his remarkable technical expertise in theory (beside experiments) for not let one think that he is not deeply lacking scientific honesty. Look at who support him: not so long ago (and for now I did not check) he had the support of some strange sect. This stinks, for me and I do not see any of that behind the paper being discussed. My understanding is that within a few month, another paper by the same author will be posted on QuantPh Arxive on
WW, superposition and taking the issue of local realism out of metaphysics into physics with application to interferences with or without delay. I am not privy of the title to look for, nor of the exact content. The Bell paper took about 4-5 years to be accepted (while long ago Pitowsky told the author that there were so many new ideas in there that the paper should appear anyway, or something of that sort).

charlylebeaugosse

That's what I thought, but I wanted to be sure: sonce that paper is anti-realist, it is as anti dBB as possible, siding strongly with Pauli and Einstein on that matter.

nikman

I genuinely don't get this. BOTH locality and realism may be false assumptions in Bell's theory. For a long time, in the wake of the Aspect experiments, it was thought that only one of them actually had to be a false assumption and the other (whichever other) might go free. Following that line of thinking Bell personally opted for the false assumption being locality, not realism, and went with Bohm and nonlocality in order to salvage realism. Then, much more recently, along come Leggett and Tresser who say okay, let's indeed assume locality is an unnecessary assumption. Accept nonlocality as read. But the Bell test results may indicate that realism is a false assumption also (Leggett is a scientist of genuine integrity: he's willing to help prove himself wrong if that's how things work out). Nothing in Bell forecloses that outcome. Both locality and realism could be false assumptions. So let's assume the truth of nonlocality and then see if realism can be tested independently.

Bell's brilliance had nothing to do with his initial belief (out of reverence for Einstein) that the conclusions of EPR ought to be correct, because they're not, nor with his acceptance of Bohmism. What he did was grasp how EPR might be tested by subjecting the assumptions of locality and realism to physical experiment. This was an unprecedented accomplishment. He was just never able to figure out how to unarguably separate locality and realism on the basis of experimental results because not even he could do everything.

charlylebeaugosse

Bell+Aspect do not allow to distinguish the false hypothesis, you are right here, but there are many indication to the contrary (including in the papers of Leggett and Tresser), while both consider that the issue is not yet settled for good. Now the 1931 paper of Einstein, Tolman, and Podolsky (ETP) is quite often overlooked. It proves that for generic particles (although they do not make the distinction, but clearly their argument does not apply to EPR particles) there is a UP when going back in time, something that seems to me very hardly compatible with realism, and certainly not with realism of the form needed by Bell:
according to ETP, if one measurement is made, perhaps that observable pre-exist but not the conjugate ones. Now Bell, after Bohm, considers the case when one spin projection is measured on each particle: how can the other spin that he needs (or the two other spin needed by CHSH, hence also by Aspect et al.) make any sense. This is why I always tell that Einstein (as well as others of his size, and as Feynman apparently did by throwing
Clauser out of his office as told in a popular book: is that true???) would have laughed of Bell paper and dismissed it as being as naive as dBB theories.

- For Einstein making fun of dBB, see the correspondence with Born;
- For the opinion by Born in that book according to which Einstein beleived in HVs, see what I wrote recently about QM compatible HVs in the thread about "Is action at a distance possible as..." , and see in the Born-Einstein correspondence how much Born lacked any understanding of what Einstein was trying to tell him about EPR type issues.
Thus, I do not consider that Bell was fair when he cited Born against Einstein or that he was even decent in the way he responded to Jammer's remarks that Einstein did not defend (naive) HVs.

So Bell was surely a brilliant scientist but the way he quoted things was not exemplary, AND the 1931 ETP is certainly what should let us have a bit less consideration for that part of Bell's work (whose job at CERN was not to take care of foundational issues).

Now, while history is fun, the real issue is physics and yes, it is unknown whether it is locality, or realism or both that have to be blamed of the contradiction, but while research has to progress in a free way, there are good reasons to believe that realism (in the naive
and microscopic sense) is what is wrong. Personaly my scientific life contains alsmost as many proofs of what I thought false as proofs of what I thought right a few years (or weeks) before (of course "proofs" means arguments in favor of something when working as physicist,but I share my time between math and physics and else). The fact is that non-locality and other things of that kind have invaded physics and the sound foundations are melting away, all helped by the lack of professionalism of most contributors to the www culture.
Let us hope that reason and good science will win at the end. I'd love to be (again) convinced of non-locality. After all, that is the beauty of two forms of information (Classical and Quantum) traveling at different speed (c and infinity) that I "learned about" when talking to Charles Bennett that lead me back to Quantum Mechanics after a long carrier in Classical Physics. Unfortunately I began to see misquotations all over the places and then many false arguments. I have feared non-realism most of my life (forgetting that even a realist word is mostly empty, forgetting that we are mostly empty). Please convince me or anyone else a bit cautious that realism holds true,even if almost empty.

DrChinese

Of course they will and are! We aren't going backwards!!

There was a spirited debate many years back over Big Bang versus Continuous Creation. BB won after the 1965 discovery of the CMBR of course. That same year saw the publication of Bell. I think it is safe to say that future discoveries will help us to sort things out. I too have a slight bias towards throwing out realism, but could be swayed anytime by a good paper.

As nikman says, clearly separating locality and realism is not so simple given experimental setups. For example: even in situations in which non-locality appears to be demonstrated, there are ways to construe the "action" such that there are no FTL influences at all. But now we draw the causal direction of time into the equation, making things really strange.

billschnieder

There is so much confusion that I would like to start my participation in this thread by suggesting that we each define what we mean by "realism".

To me, realism means, "elements of reality" exist independent of observation, or observability. To me realism has nothing to do with instrumental behaviour or whether these "elements" can be directly observed without disturbance or not. To me, when you say a photon is emitted but not detected, you are admitting to my definition as above. As far as I can tell from this thread so far, all participants believe realism as defined above is true even if they haven't explicitly admitted it. If anyone else thinks realism as defined above is false, please state it and I will show using your own quotes that you are lying. However, you may think "realism" means something else and it is important we all agree what we are arguing for or against to avoid confusion.

Now some will argue that the EPR definition of realism is the idea that a single particle (or entangled pair) will have definite spin projections at 3 different angles. I do not agree that this is the EPR definition but I am willing to grant that definition for the sake of argument, so long as we are not later on drawing conclusions about the previous definition I gave above, based on this so called "EPR definition". In any case, I will suggest first that we present clearly the definition of realism we would like to argue, and then when all the parameters of this version of "realism" have been exposed, it will then make sense to question whether QM or Experiments in anyway tell us anything about the "realism" we are discussing.

DevilsAvocado

Yes, and the funny thing is that Sir Fred Hoyle, who coined the term "Big Bang", stuck to his own Steady State theory until he passed away in 2001, denying BB aggressively!

And what is almost funnier is that Hoyle promoted the theory that life evolved in space, spreading through the universe via panspermia, and that evolution on earth is driven by a steady influx of viruses arriving via comets.

It’s hard to be a heretic!


(P.S: Speak of the devil! )

DrChinese

1. I agree with this.

2. I miss how this is different than 1. EPR said it was reasonable to admit as "real" 2 or more elements even if they could not be predicted simultaneously. So 3 different angles would quality as EPR realism as I read it. So are you saying a) that you don't think EPR says this, or b) that you do not agree with this idea, regardless of whether EPR says it?

DrChinese

1. That is sad.

2. I guess anything is possible. I have been called a virus by some people...

billschnieder

1) I'm not sure I understand your point. Are you agreeing that my definition of "realism" in (1) is correct, or are you admitting that whatever that definition entails about the universe is true. There is a difference there. There are four possibilities

a) You agree that "realism" is defined as I did, but believe that "realism" so defined is false.
b) You disagree that "realism" is defined as I did, in which case you probably have your own definition. In addition you also believe what my definition implies about the universe, is false.
c) You disagree that realism is defined as I did but believe that, what my definition implies about the universe is true. In this case you will still have to provide your own definition of "realism".
d) You agree that realism is defined as I did, and what it implies about the universe is also True. In this case, we are in total agreement and the discussion around Bell's theorem will have to be about something other than "realism".

2) My definition of realism says nothing about predictability or observability. All it says is that "there exists, elements of reality independent of observation". If somebody says "The moon does not exist when no one is looking", they are rejecting my definition.

The so called "EPR definition" is more restrictive in the following sense. If a particle has a pre-existing attribute, which can never be directly measured, but which together with an attribute of the instrument, produce a measurable phenomenon, the so called "EPR definition" will classify this as "unreal", even though it is very real according to my definition. In other words, if you define realism as "observables" must "pre-exist" the act of "observation", then you are proposing a more restrictive view which ignores the obvious fact that some observables are created during the measurement process.

In the EPR scenario you have a spin, but you do not measure the spin, you measure it's projection. But the projection is meaningless unless you project it to something, and this something is defined by the instrument angle. Therefore the spin projection of a particle is just one example of an obvious case in which the observable is created on observation. So if you have defined realism in such a narrow way, you can not then conclude that the spin of the particle does not exist until it is measured. This is why I say we have to be clear about what definition of realism we are using. You do not need Bell to see that such a narrowly defined "realism" which is often erroneously ascribed to EPR, is a naive definition.

DrChinese

1. I agree with your definition as stated. I don't necessarily agree that elements of reality exist independently of observation. I tend to reject that view.

2. According to EPR: if that spin's projection can be predicted with certainty, then the pre-existing spin must itself real - independent of the instrument by which it is measured.

If the EPR definition is more "restrictive" than yours: what does EPR define as unreal that you define as real? Because I cannot see the difference. EPR specifically defines as real observables whose values can be predicted - don't you? They say there is a matching element of reality to the observable. Not that the observable (projection) itself is real.

If your definition is less restrictive than EPR's, then more qualifies as real. Which would naturally make it easier to falsify. So I guess I see that point which you are making. But what evidence would you cite for us to accept your definition over EPR's? I mean, predicting with certainty seems like a pretty strong position.

(The EPR definition is LESS restrictive than the QM definition - which of course would be only those items which can be simultaneously predicted.)

billschnieder

Fair enough.
It is the spin which pre-exists the observation, not the "spin projection", yet it is the "spin projection" which is observable not the spin. So clearly, if the EPR definition is that "observables must pre-exist measurement", it is not a reasonable definition because as you have agreed in (1), realism simply means "elements of reality" (not "observables") pre-exist observation". In other words, it is possible for realism as defined and agreed in (1) to be true, in a completely contextual universe in which nothing can be directly observed, but in which pre-existing elements of reality always interact with instruments to reveal observables. But contextual observables are not allowed in a universe in which observables must pre-exist observation.

If the EPR definition is that "observables must pre-exist observation", then contextual observables are not allowed. But in my definition, contextual observables are fully consistent with pre-existing "elements of reality". But if you are willing to agree that underlined text above is not the EPR definition, and will rather say that my original definition which you agreed to is the EPR definition, then that is a good point to start, and we can proceed to discuss the burden of proof required to disprove it.

DevilsAvocado

Caroline H. Thompson?

zonde

It should definitely help to follow this discussion.

I would say that while this definition is "true" it is not restrictive enough to have some value.
Because you can arrive at situation where "elements of reality" are completely independent from results of observations.
I think that definition should include some statement how "elements of reality" are related to observations. Say "elements of reality" ascribed to particle together with "elements of reality" ascribed to measurement equipment (conditions) determine observed result.

This is not EPR definition. EPR definition covers only the case when say projection of spin is predictable with certainty. And because this definition involves "prediction" it can start a looong discussion.

zonde

This violation of "Effect After Cause Principle" seems quite paradoxical. I think I agree with Dmitry:
If we can relate event that has happened before (memory) with another event that just happened (senses) then event in memory is cause by definition and event reported by senses is effect by definition and to say that effect and cause can swap places means that we should alter memory and simulate sensory information. But in that case we can't be sure about anything and I prefer to be sure about something rather than nothing.

DrChinese

Probably worse...