non-locality vs relativity

Just to get some cool conversation going, which one do yous guys think has wider implications? From a 'wanting-to-explain-it-all" standpoint.

Cambraceres

[bjarne]

Umm, you might want to develop a bit further on that question.

[J. Stew]

Non-locality, where is your mind but everywhere.

What I'm asking is, which discrete theory has wider implications in the overall scheme of things, non-locality(as proven by Aspect), or relativity, as elucidated by Einstein?

Cambraceres

[bjarne]

I'm vaguely familiar with both Aspect's experiment and the theory of relativity. My question was more the somewhat fuzzy in the question

"in the overall scheme of things"

If it is about consistency of theories there is to my knowledge no conflict between the non-local nature of correlations exhibited in quantum mechanical measurments and causality [relativity].

The "nonlocality" you speak of (since you mention Aspect -- there are other types of nonlocality, e.g. nonlocal field theories, but these are usually regarded as "bad" and unphysical) is really just quantum mechanical entanglement over spacelike intervals. In terms of explaining things, it really is just a demonstration that the world is fundamentally quantum mechanical -- i.e. Bell's inequalities (which should hold in any classical universe) are violated.

Relativity in this context means that you can't use entanglement to transmit information faster than the speed of light.

As for my own speculation on what an "ultimate, background free theory of the universe" might look like -- I would tend to think that quantum mechanics (or some generalization of it) is truly fundamental, whereas the notion of a spacetime manifold (which defines relativity and locality) may be an emergent property. Some may disagree, however -- string theory, for example, requires lorentz invariance to be an exact local symmetry of the theory, down to arbitrarily small distance scales.

[bjarne]

Space time as an emergent property is an interesting idea although from what I've heard of quantum cosmology so far I don't feel very convinced about the present ideas. But feel free to develop you ideas a bit more.

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Space time as an emergent property is an interesting idea although from what I've heard of quantum cosmology so far I don't feel very convinced about the present ideas. But feel free to develop you ideas a bit more.

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There are two guiding principles behind this notion -- one is that there should be as little "background structure" in the final theory as possible. The general theory of relativity is "background free" in the sense that there is no preferred geometry -- the geometry arises as a solution to a dynamical equation. Some people would like to take this further -- that the manifold structure itsself arises from dynamical equations rather than simply being required for the formulation of the theory. The other principle is the idea that there should be a finite number of degrees of freedom in a physical theory -- quantum field theory and superstring theory have an infinite number of degrees of freedom, in a sense due to their formulation on a spacetime manifold. Introducing infinities from the start in what is supposed to be the "final" theory makes some people (including me) uncomfortable.

It thus seems like a reasonable proposition that the fundamental theory could be composed of a finite (but large) number of degrees of freedom that resemble a manifold with the usual Lorentz symmetry at sufficiently large distance scales. How to arrive at such a theory, though, is obviously the hard part. "Loop quantum gravity" takes a stab at it -- it is "background free" -- but nobody knows how to check and see if it would give the correct large scale limit, and there are reasons to be skeptical that it should.

[bjarne]

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The other principle is the idea that there should be a finite number of degrees of freedom in a physical theory -- quantum field theory and superstring theory have an infinite number of degrees of freedom...

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