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Locality & Determinism beneath the quantum surface?

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Fyzix
#1
May2-11, 06:33 PM
P: 172
It seems everyone think that Bell Inequalities rules out any hope of ever getting a local and deterministic account of reality.
This need not be so...

Gerard 't Hooft (Nobel Prize winner of 1999) has been working on a theory that may explain the quantum behaviour in a classical way.


Layman link:
http://sdsu-physics.org/physics180/p..._freewill.html

Technical link:
http://arxiv.org/PS_cache/quant-ph/p.../0604008v2.pdf
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JesseM
#2
May2-11, 07:51 PM
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P: 8,470
Where does it say his model is a local one?

Edit: this wikipedia article does say at the bottom that he is interested in finding a local model by exploiting the superdeterminism loophole (though I am not sure that your links actually concerns such a model), which I think is equivalent to the "no-conspiracy assumption" which is always mentioned in any rigorous proof of Bell's theorem (for example, see section D on p.6 of this proof). A violation of this condition is logically possible but would be physically bizarre, it would mean for example that if an experimenter chose on a whim each day whether to have cereal, pancakes or an omelet for breakfast, and on each day used this seemingly random choice to decide which detector setting to use for a particle which had been in flight for exactly a year, then one year earlier the laws of physics must have behaved as if they were "choosing" what hidden variables to assign to the particle based on what the experimenter would decide to have for breakfast one year later.
Fyzix
#3
May2-11, 08:11 PM
P: 172
He mentions locality in this article:
http://star.tau.ac.il/~eshel/Bio_com...oft-Hidden.htm

JesseM
#4
May2-11, 08:19 PM
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P: 8,470
Locality & Determinism beneath the quantum surface?

Quote Quote by Fyzix View Post
He mentions locality in this article:
http://star.tau.ac.il/~eshel/Bio_com...oft-Hidden.htm
You mean the very end part? They don't quote t'Hooft himself in that last section, just someone talking about his ideas, and the guy doesn't exactly say his hoped-for model would be fully local, but rather that this type of model "represents a kind of compromise" between two views that aren't explained very clearly (they describe one view as saying that quantum correlations are "real" while the deterministic view "rules them out", but I don't know exactly what either statement would mean at a more technical level).
JesseM
#5
May2-11, 08:40 PM
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P: 8,470
Quote Quote by Fyzix View Post
He mentions locality in this article:
http://star.tau.ac.il/~eshel/Bio_com...oft-Hidden.htm
Incidentally, I see that Richard Gill, who is quoted making the comments about locality in the last section of the article, also has a paper here where he talks about t'Hooft and superdeterminism on p. 19-20:
’t Hooft and predetermination

’t Hooft notes that at the Planck scale experimenters will not have much freedom
to choose settings on a measurement apparatus. Thus Bell’s position 2
gives license to search for a classical, local, deterministic theory behind the
quantum mechanical theory of the world at that level. So far so good.
However, presumably the quantum mechanical theory of the world at
the Planck scale is the foundation from which one can derive the quantum
mechanical theory of the world at levels closer to our everyday experience.
Thus, his classical, local and deterministic theory for physics at the Planck
scale is a classical, local and deterministic theory for physics at the level of
present day laboratory experiments testing Bell’s theorem. It seems to me
that there are now two positions to take. The first one is that there is, also
at our level, no free choice. The experimenter thinks he is freely choosing
setting label number 2 in Alice’s wing of the experimenter, but actually the
photons arriving simultaneously in the other wing of the experiment, or the
stuff of the measurement apparatus there, “know” this in advance and capitalize
on it in a very clever way: they produce deviations from the Bell inequality,
though not larger than Cirel’sons quantum bound of 2√2 (they are,
after all, bound by quantum mechanics). But we have no way of seeing that
our “random” coin tosses are not random at all, but are powerfully correlated
with forever hidden variables in measurement apparatus far away. I find it
inconceivable that there is such powerful coordination between such totally
different physical systems (the brain of the experimenter, the electrons in the
photodetector, the choice of a particular number as seed of a pseudo-random
number generator in a particular computer program) that Bell’s inequality
can be resoundingly violated in the quantum optics laboratory, but nature as
a whole appears “local”, and randomizers appear random.

Now “free choice” is a notion belonging to philosophy and I would
prefer not to argue about physics by invoking a physicist’s apparently free
choice. It is a fact that one can create in a laboratory something which looks
very like randomness. One can run totally automated Bell-type experiments
in which measurement settings are determined by results of a chain of separate
physical systems (quantum optics, mechanical coin tossing, computer
pseudo-random number generators). The point is that if we could carry out
a perfect and succesful Bell-type experiment, then if local realism is true an
exquisite coordination persists throughout this complex of physical systems
delivering precisely the right measurement settings at the two locations to
violate Bell’s inequalities, while hidden from us in all other ways.

There is another position, position 5: the perfect Bell-type experiment
cannot be made. Precisely because there is a local realistic hidden layer
to the deepest layer of quantum mechanics, when we separate quantumentangled
physical systems far enough from one another in order to do separate
and randomly chosen measurements on each, the entanglement will
have decayed so far that the observed correlations have a classical explanation.
Loopholes are unavoidable and the singlet state is an illusion.
The first position he describes seems analogous to my example where the laws of physics seem to choose the properties to assign to a particle based on what an experimenter will decide to have for breakfast one year later, but I don't quite understand what he's talking about in that last paragraph, I guess it's basically that a loophole-free Bell test would turn out to be impossible for some reason.
Fyzix
#6
May2-11, 08:58 PM
P: 172
I'm not sure, but perhaps this will shed some light on the situation:

http://arxiv.org/PS_cache/arxiv/pdf/...908.3408v1.pdf
DrChinese
#7
May3-11, 12:18 AM
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P: 5,289
Quote Quote by Fyzix View Post
I'm not sure, but perhaps this will shed some light on the situation:

http://arxiv.org/PS_cache/arxiv/pdf/...908.3408v1.pdf
You know, any ad hoc theory can explain things. Yet it will be completely useless as science.

Just as Bell demonstrated that realism leads to testable requirements, a serious theory of super-determinism will do the same. In essence, this would require every particle to contain all information about all particles everywhere.

Howsa 'bout something that actually explains or predicts something?


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