Local or Nonlocal?

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The concept of “fields” told us that our physics is local, while the concept of "entanglement" seems to say that there is something nonlocal

So I wonder whether our physics laws are local?
 

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  • #2
A. Neumaier
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The concept of “fields” told us that our physics is local, while the concept of "entanglement" seems to say that there is something nonlocal

So I wonder whether our physics laws are local?

The meaning of ''local'' in quantum field theory and in discussions of Bell inequalities is totally different. As always in language, you must respect the context to make sense out of statements involving words with multiple meanings.
 
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The field operator is a local object, but a product of two or more field operators at different points is a nonlocal object. When such nonlocal objects act on the vacuum, one gets a many-particle state, which may contain nonlocal features. (More precisely, one must take a superposition of such states to get entanglement, i.e., really nonlocal features.)
 
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The meaning of ''local'' in quantum field theory and in discussions of Bell inequalities is totally different. As always in language, you must respect the context to make sense out of statements involving words with multiple meanings.

I don't think that "local" in terms of quantum field theory was in mind in the OP, but the notion that gravitational force, for instance, is not a result of action at a distance but the result of local fields. This notion is applied in the EPR argument against quantum mechanical completeness.
 
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A. Neumaier
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I don't think that "local" in terms of quantum field theory was in mind in the OP, but the notion that gravitational force, for instance, is not a result of action at a distance but the result of local fields. This notion is applied in the EPR argument against quantum mechanical completeness.

Possibly; then we'd have three totally different meanings of locality. But in fact Einstein locality and locality in QFT are essentially the same thing, guaranteeing that the dynamics is hyperbolic, with a maximal speed of transport.

In any case, correlations are not transported, hence nonlocal correlations have nothing to do with Einstein locality.
 
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The concept of “fields” told us that our physics is local, while the concept of "entanglement" seems to say that there is something nonlocal

So I wonder whether our physics laws are local?

Evey quantum state which isn't a position eigenstate is non local i'd say.
 
  • #7
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The field operator is a local object, but a product of two or more field operators at different points is a nonlocal object. When such nonlocal objects act on the vacuum, one gets a many-particle state, which may contain nonlocal features. (More precisely, one must take a superposition of such states to get entanglement, i.e., really nonlocal features.)

Do you mean by that that linear super-position for numerical quantities (in Hilbert space) is no longer valid for non-local features? In other words the math goes "non-linear"? Or do you mean that expected symmetries get broken?
 
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Do you mean by that that linear super-position for numerical quantities (in Hilbert space) is no longer valid for non-local features? In other words the math goes "non-linear"? Or do you mean that expected symmetries get broken?
No, no, no.

A product and a sum of linear operators is still a linear operator.
 
  • #9
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Possibly; then we'd have three totally different meanings of locality. But in fact Einstein locality and locality in QFT are essentially the same thing, guaranteeing that the dynamics is hyperbolic, with a maximal speed of transport.

In any case, correlations are not transported, hence nonlocal correlations have nothing to do with Einstein locality.

I don't see this as easily deducible from experimental results. How do you arrive at the conclusion that correlations are not transported?
 
  • #11
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The concept of “fields” told us that our physics is local, while the concept of "entanglement" seems to say that there is something nonlocal

So I wonder whether our physics laws are local?

I recently said in a thread, that one axiom of quantum mechanics might be that:

''Non-locality is strictly a quantum phenomena. Whilst local conditions can be met quite well for arbitrarily large bodies.''

Our universe is not simply local. It is nonlocal as well, but never one always over the other. It's like accepting how tunnelling, and quantum interference patterns are accepted quantum phenomena, you never observe them therefore for bodies which are considered free of quantum effects. Non-locality seems to be similar in this regards and completely absent for macroscopic bodies.
 
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A. Neumaier
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I don't see this as easily deducible from experimental results. How do you arrive at the conclusion that correlations are not transported?

Correlations are things one computes from statistics on observations.

Transported are mass, energy, charge, momentum, etc..
 
  • #13
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I don't think that "local" in terms of quantum field theory was in mind in the OP, but the notion that gravitational force, for instance, is not a result of action at a distance but the result of local fields.

i agree
cos he ask:

So I wonder whether our physics laws are local?

the gravity on the earth have nothing to do with some dust at UDFy-38135539.
 
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