Experimental Test Limits Predictive Power Beyond Quantum Theory

[DrChinese]

As an example of how far things have come post Bell/Aspect, here is a just announced experimental test which limits any future expectations one might have on "completing" QM:

An experimental test of all theories with predictive power beyond quantum theory, Terence E. Stuart, Joshua A. Slater, Roger Colbeck, Renato Renner, Wolfgang Tittel (2011)


Abstract:
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"According to quantum theory, the outcomes of future measurements cannot (in general) be predicted with certainty. In some cases, even with a complete physical description of the system to be measured and the measurement apparatus, the outcomes of certain measurements are completely random. This raises the question, originating in the paper by Einstein, Podolsky and Rosen, of whether quantum mechanics is the optimal way to predict measurement outcomes. Established arguments and experimental tests exclude a few specific alternative models. Here, we provide a complete answer to the above question, refuting any alternative theory with significantly more predictive power than quantum theory. More precisely, we perform various measurements on distant entangled photons, and, under the assumption that these measurements are chosen freely, we give an upper bound on how well any alternative theory could predict their outcomes. In particular, in the case where quantum mechanics predicts two equally likely outcomes, our results are incompatible with any theory in which the probability of a prediction is increased by more than ~0.19. Hence, we can immediately refute any already considered or yet-to-be-proposed alternative model with more predictive power than this. "


Conclusion:
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"In conclusion, under the assumption that measurements can be chosen freely, no theory can predict measurement outcomes substantially better than quantum mechanics. In other words, any already considered or yet-to-be-proposed theory that makes signi cantly better predictions would either be incompatible with the experimental observations presented herein, or be incompatible with our assumption that the measurement parameters can be chosen freely. While the former is true, for example, for local hidden variable theories (as already pointed out by Bell [2]) or for the Leggett model [4], the de Broglie-Bohm theory [29, 30] is an example of the second type|the theory cannot incorporate measurement parameters that satisfy our free choice assumption."

This is not a Bell test, and uses different logic to achieve their conclusions. They claim that dBB type theories are incompatible with freely chosen measurement parameters. Enjoy!

-DrC

 

[unusualname]

haha, but wait for rebuttal, I'm sure dbb can hang on a while longer.

 

[Demystifier]

They claim that dBB type theories are incompatible with freely chosen measurement parameters.

Of course they are, according to dBB everything is determined by initial conditions in the far past, there is no room for free will. Which, of course, makes dBB compatible with their results.

By the way, their main result is somewhat similar to the free-will theorem by Conway and Kochen.

 

[Demystifier]

The only unfair thing about this very interesting paper is its title: Instead of "all theories" they should write "all theories compatible with freely chosen measurements", as they write in the rest of the paper. With the present unfair title, they cause wrong impressions by those who read only the titles.

 

[Demystifier]

haha, but wait for rebuttal, I'm sure dbb can hang on a while longer.

Even the authors of this paper say that dBB is compatible with their results, so there is no need for a rebuttal from a Bohmian side.

 

[Fyzix]

Demystifier don't waste your breath on unusualname, he believes he has the secret that has solved QM but that the science community is in on a big conspiracy to keep it secret.

 

[Dmitry67]

Of course they are, according to dBB everything is determined by initial conditions in the far past, there is no room for free will. Which, of course, makes dBB compatible with their results.

There is a difference between (A) claiming that theory is (super)deterministic (which is obvious for all deterministic theories, including classical mechanics) and (B) using it as a loophole for some particular case (say, Bell), because (B) assumes some 'consipiracy' from nature, some pre-adjustment of initial conditions to fit some ad-hoc experiment.

(B) is much stronger than (A). For example, many people can accept (A), but not (B) as an option to 'save' local realism in Bell. Have Demistifier switched from (A) to (B) protecting dBB?

 

[Demystifier]

Dmitry, I think the difference between (A) and (B) is very subtle, and I have not yet seen a paper that CLEARLY AND GENERALLY explains what exactly the difference is. So at the moment, I cannot definitely answer your very interesting and important question. But I hope I will in the future. When (and if) I do that, I will let you know.

What I can say for certain at the moment is that (B) is not needed for Bell, GHZ, and Hardy, because in these cases nonlocality is enough.

 

[Demystifier]

OK, now I have studied the experimental paper above and the theoretical paper (by the same authors) they refer to, so now I better understand what is REALLY going on.

In short, the authors are manipulators. By that, I mean they play with words with the intention to create false impressions, without actually lying. This is something that usually lawyers and advertisers do without being accused for cheating, but in science it is a kind of cheating that should not be allowed.

Their manipulation consists in the following. They choose words that create a false impression that locality is NOT one of the assumptions. Yet, when one carefully reads what they really mean by certain words, one can see that locality IS one of their assumptions.

In particular, in the Conclusion of the experimental paper they say "... de Broglie-Bohm theory is an example of the second type -- the theory cannot incorporate measurement parameters that satisfy our free choice assumptions". But to see what their "free choice assumptions" really are, one must read their earlier theoretical paper (written by two of the authors of the experimental paper)
http://lanl.arxiv.org/abs/1005.5173 v2
which, by the way, is not published in a peer-reviewed journal (and I hope it never will in the present form, due to the unfair manipulation involved). Their "free choice assumptions" are written explicitly at page 2, the top of the second column, in italic letters. In particular, note the crucial part of their assumption "... that do not lie in the future lightcone of A". It is THAT part of their FR assumption, and not the free choice of measurement itself, that is crucial for an explanation why dBB is compatible with their results. In other words, dBB is OK not because it cannot accommodate free choices of measurements, but because it is nonlocal. (Dmitry, this is the answer to your question.)

They do not mention this locality assumption almost anywhere else, except at one additional place: the footnote 11. In that footnote, the assumption of locality is rather explicit. Thus, there are no doubts that their result is much less general than they want us to believe. Their result refers only to local theories, and they are aware of that, but they know that the paper would not be so sexy if they said it too explicitly. So they manipulate by hiding it in an unfair choice of words (and in a footnote with a more fair choice of words).

 

[Demystifier]

The only unfair thing about this very interesting paper is its title: Instead of "all theories" they should write "all theories compatible with freely chosen measurements", as they write in the rest of the paper. With the present unfair title, they cause wrong impressions by those who read only the titles.

In view of my last post, I must withdraw the claim above. The paper is much more unfair than I thought at first. The locality is one of their crucial assumptions, but at most places where it should be said explicitly - they simply don't say it. One must read the papers very carefully to find out where do they say it explicitly.

 

[Demystifier]

Dmitry, I think the difference between (A) and (B) is very subtle, and I have not yet seen a paper that CLEARLY AND GENERALLY explains what exactly the difference is. So at the moment, I cannot definitely answer your very interesting and important question. But I hope I will in the future. When (and if) I do that, I will let you know.

What I can say for certain at the moment is that (B) is not needed for Bell, GHZ, and Hardy, because in these cases nonlocality is enough.

In view of my post #9 above, now I can say that (B) is also not needed for the the paper we discuss here, because in this case nonlocality is enough as well. There is no need for a conspiracy at all!

 

[Dmitry67]

Thank you.
I feel relieved because in fact the claim in the article was too strong.