On 2/05/2016 3:31 pm, Jesse Mazer wrote:
On Mon, May 2, 2016 at 1:10 AM, Bruce Kellett <[email protected] <mailto:[email protected]>> wrote:On 2/05/2016 1:31 pm, Jesse Mazer wrote:On Sun, May 1, 2016 at 8:49 PM, Bruce Kellett <[email protected] <mailto:[email protected]>> wrote: On 2/05/2016 7:52 am, Jesse Mazer wrote:On Fri, Apr 29, 2016 at 8:32 PM, Bruce Kellett <[email protected] <mailto:[email protected]>> wrote: That is a semantic matter. There is a problem if one insists that "non-local" means the propagation of a real physical influence (particle of wave) faster-than-light. But "non-locality" in standard quantum usage means the above -- the entangled state acts as a single physical unit even when its components are widely separated. I agree it's a semantic matter, but your description of the "standard quantum usage" doesn't seem to be accurate. Among physicists, the standard understanding of "local" and "non-local" in the context of Bell's theorem and relativity is the one I cited earlier--a theory is "local" if and only if the function that gives you the value of local variables at any given point P in spacetime (or gives the best possible probabilistic prediction about their values, in the case of a non-deterministic theory) only requires as input the values of local variables at other points that lie within P's past light cone, whereas a "non-local" theory would be one where the function requires knowledge of variables at a spacelike separation from P to generate the best possible prediction. As I mentioned, I think this is explained most clearly in Bell's paper "La nouvelle cuisine" which you can find in the collection "Speakable and Unspeakable in Quantum Mechanics", and you can also find it discussed in other sources, http://arxiv.org/abs/0707.0401 for example. As for "acts as a single physical unit", that seems like a decidedly non-mathematical definition which physicists would steer clear of, unless you can provide a mathematical formalization or what you mean, or cite a mainstream source that provides one.I don't see any paper of the title you mention in my copy of "Speakable and Unspeakable in Quantum Mechanics", could you give a page number reference? It's on p. 232 of the 2nd edition, chapter 24.I have now looked at the paper by Norsen. It seems that the more detailed definiton of locality does little more than remove the notion of "superdeterminism" from the equation -- the idea that things in the common past of A and B could conspire to give rise to the correlations.The paper by Norsen at http://arxiv.org/pdf/0707.0401v3.pdf does mention the issue of ruling out superdeterminism, but that wasn't what I was referring to when I talked about the definition in La nouvelle cuisine which is repeated in Norsen's paper. Rather I was talking about equation 1 on page 4 whose physical meaning in terms of past light cones is show in Fig. 2 on the same page. Referring to the diagram and equation, b1 refers to the physical state of local variables in region 1, b2 refers to the physical state of local variables in another region 2 at a spacelike separation of 1, and B3 refers to some sufficiently detailed set of local states in region 3 which is in the past light cone of region 1, but entirely outside the past light cone of region 2. The idea is that by picking a sufficiently detailed set for your B3, you can have it so that once you know B3, additional knowledge of b2 is irrelevant to your prediction of what's going on in b1, i.e. you don't need anything outside the past light cone of 1 to make the best possible physical prediction about the physical facts in that region. So, nothing to do with superdeterminism, just a more formal statement of the idea I described earlier about the function for making predictions about a given region depending only on facts in the past light cone of that region.
And that is all I have ever claimed about locality -- that is what is built into the formal quantum description of the state. The more elaborate definition does not add anything substantive - it merely rules out some alternative formulations of the state that go beyond standard QM.
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