Four-qubit entanglement from string theory

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bcrowell
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Main Question or Discussion Point

"Four-qubit entanglement from string theory"

This paper

Borsten et al., "Four-qubit entanglement from string theory," http://arxiv.org/abs/1005.4915 (published in PRL)

is being described

http://www.sciencedaily.com/releases/2010/09/100901091938.htm

in the popular press as a proposal for an experimental test of string theory. Unfortunately I'm not technically adept enough to understand much of the paper. Is this an accurate description, or is the paper really just finding a mathematical equivalence between two theories, one of which describes testable physics and one of which describes Planck-scale physics that we can't test experimentally?

Since string theory isn't really a theory yet, I'm also not clear on how we can talk about testing it. Is this a case where all versions of string theory make certain generic predictions, so it doesn't matter which version of string theory we're talking about?

Suppose the four-qubit entanglement experiment is carried out, and the results are not as predicted by this theory that's mathematically equivalent to string theory. Does that mean string theory is wrong? I.e., does this really expose string theory to the risk of being falsified?
 

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marcus
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We already have a thread about that May paper (1005.4915) and the ensuing press releases. I'll get the link.

Yeah, here is the earlier thread:
https://www.physicsforums.com/showthread.php?t=425922

It was started by Kevin_Axion on 1 September.

I posted this response:


That "test" was already debunked 27 May.
http://www.math.columbia.edu/~woit/wordpress/?p=2977
The preprint came out in May. Here it is:
http://arxiv.org/abs/1005.4915
Four-qubit entanglement from string theory

The press release from Imperial College contains some hype. Over interpreting the paper (which was just published) as a test of string as fundamental physics. Often times a public relations department will puff something up around the time the paper is published in journal.

So when the public relations release came out, and was picked up by, for example, PhysOrg (where you saw it) Woit blogged again about it:
http://www.math.columbia.edu/~woit/wordpress/?p=3127

Interestingly enough the PR department at Imperial College London then pulled in their horns! :biggrin: They actually changed the title of the press release to something a bit more reserved:


The original title on the press release has been changed. It used to be “New study suggests researchers can now test the ‘theory of everything’”.

The new title does not say "test". Now it’s “New study presents unexpected discovery that string theory may predict the behaviour of entangled quantum particles.



In other words, it is not a test of Superstring as a fundamental theory of matter or a "ToE". It is an application of some stringy mathematics to calculate stuff in quantum information theory--typically larger scale behavior. String has a repertory of math techniques that have already been used to study largescale stuff: superconductivity (a branch of condensed matter physics) and nuclear physics (not fundamental particle).

In this case it seems the calculation had already been done by other means, but stringy math was applied, and also succeeded.

Woit's comment:
"I have no idea how this paper is supposed to contain a “test” of string theory. The simple quantum mechanics problem at issue comes down to classifying orbits of a group action on a four-fold tensor product, exactly what Wallach worked out in detail in his notes, as an example of Kostant-Rallis. If you do an experiment based on this and it doesn’t work, you’re not going to falsify string theory (or Kostant-Rallis for that matter). By now there’s a long history of rather outrageous press releases being issued about the discovery of supposed “tests” of string theory. This one really takes the cake…"​
 
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marcus
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The direct answer to the question you raised seems to be:

No, it is not a test of string theory as a theory of nature, but rather an application of stringy math to something else (quantum information theory).

It does not offer the prospect of testing the string framework and invalidating it as an approach to describing fundamental physics if some experimental result is not observed.

The Imperial College PR headline originally said "test" and that was picked up by several other media---leading to some confusion. But then Imperial PR changed the headline so it no longer says that.
 
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This is why my "science" education is bad, those guys were my lecturers
 
  • #5
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Minor miscommunication, it happens, not even scientists are perfect.
 

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