[SEQ RERUN] Bell's Theorem: No EPR "Reality"

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6 [SEQ RERUN] Bell's Theorem: No EPR "Reality"

25th Apr 2012

1 min read

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Today's post, Bell's Theorem: No EPR "Reality" was originally published on 04 May 2008. A summary (taken from the LW wiki):

(Note: This post was designed to be read as a stand-alone, if desired.) Originally, the discoverers of quantum physics thought they had discovered an incomplete description of reality - that there was some deeper physical process they were missing, and this was why they couldn't predict exactly the results of quantum experiments. The math of Bell's Theorem is surprisingly simple, and we walk through it. Bell's Theorem rules out being able to locally predict a single, unique outcome of measurements - ruling out a way that Einstein, Podolsky, and Rosen once defined "reality". This shows how deep implicit philosophical assumptions can go. If worlds can split, so that there is no single unique outcome, then Bell's Theorem is no problem. Bell's Theorem does, however, rule out the idea that quantum physics describes our partial knowledge of a deeper physical state that could locally produce single outcomes - any such description will be inconsistent.

Discuss the post here (rather than in the comments to the original post).

This post is part of the Rerunning the Sequences series, where we'll be going through Eliezer Yudkowsky's old posts in order so that people who are interested can (re-)read and discuss them. The previous post was Entangled Photons, and you can use the sequence_reruns tag or rss feed to follow the rest of the series.

Sequence reruns are a community-driven effort. You can participate by re-reading the sequence post, discussing it here, posting the next day's sequence reruns post, or summarizing forthcoming articles on the wiki. Go here for more details, or to have meta discussions about the Rerunning the Sequences series.

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6 [SEQ RERUN] Bell's Theorem: No EPR "Reality"

by MinibearRex

25th Apr 2012

1 min read

6

Today's post, Bell's Theorem: No EPR "Reality" was originally published on 04 May 2008. A summary (taken from the LW wiki):

(Note: This post was designed to be read as a stand-alone, if desired.) Originally, the discoverers of quantum physics thought they had discovered an incomplete description of reality - that there was some deeper physical process they were missing, and this was why they couldn't predict exactly the results of quantum experiments. The math of Bell's Theorem is surprisingly simple, and we walk through it. Bell's Theorem rules out being able to locally predict a single, unique outcome of measurements - ruling out a way that Einstein, Podolsky, and Rosen once defined "reality". This shows how deep implicit philosophical assumptions can go. If worlds can split, so that there is no single unique outcome, then Bell's Theorem is no problem. Bell's Theorem does, however, rule out the idea that quantum physics describes our partial knowledge of a deeper physical state that could locally produce single outcomes - any such description will be inconsistent.

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buybuydandavis14y40

Is there any place we can see actual data on one of the photon polarization experiments? Not statistics, but actual data? And a probabilistic analysis, a la Jaynes, of the data?

In theory, I'm fine with non local interactions, but I'm not yet convinced they are necessary. I don't see anything about detector efficiency here, which I believe is key to the reality of what happens. It seems completely natural to me that if a photon had some directional local variable, that it would effect the likelihood of detection in a polarizer dependent on the direction of the polarizer.

Jaynes has reservations about Bell's Theorem, and they made a fair amount of sense to me. And in general I find it good policy to trust him on how to properly interpret probabilistic reasoning.

Jaynes paper on EPR and Bell's Theorem: http://bayes.wustl.edu/etj/articles/cmystery.pdf

Jaynes speculations on quantum theory: http://bayes.wustl.edu/etj/articles/scattering.by.free.pdf

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A1987dM14y20

Jaynes is misunderstanding the class of hidden-variable theories Bell's theorem rules out: the point is that the hidden variables λ would determine the outcome of measurements, i.e. P(A|aλ) is 0 for certain values of λ and 1 for all other values, and likewise for P(B|bλ), in which case P(A|abλ) must equal P(A|aλ), P(B|Aabλ) must equal P(B|bλ), and eq. 14 does equal eq. 15. (I had noticed this mistake several years ago, but I didn't know whom to tell about.)

4Manfred14y

If you're going to use an authority heuristic, at some point you also have to apply the heuristic "what does pretty much everyone else think?"

0DanielVarga14y

Very cool paper. But I couldn't understand the most important point. Can anyone help? When Jaynes says that (15) is the correct factorization instead of Bell's (14), he gives up something, and I don't understand what it is. What are the spooky conclusions that mainstream physicists wanted to avoid by working with (14) instead of (15)? I understand Jaynes' point about Bell's hidden assumptions (1) (bottom of page 12), and I agree with it. But I don't understand what he says about hidden assumption (2).

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