On 2/05/2016 3:31 pm, Jesse Mazer wrote:
On Mon, May 2, 2016 at 1:10 AM, Bruce Kellett
<bhkell...@optusnet.com.au <mailto:bhkell...@optusnet.com.au>> wrote:
On 2/05/2016 1:31 pm, Jesse Mazer wrote:
On Sun, May 1, 2016 at 8:49 PM, Bruce Kellett
<bhkell...@optusnet.com.au <mailto:bhkell...@optusnet.com.au>> wrote:
On 2/05/2016 7:52 am, Jesse Mazer wrote:
On Fri, Apr 29, 2016 at 8:32 PM, Bruce Kellett
<bhkell...@optusnet.com.au
<mailto:bhkell...@optusnet.com.au>> 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.
Bruce
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