On 3/05/2016 1:49 am, Bruno Marchal wrote:
On 02 May 2016, at 07:54, Bruce Kellett wrote:
On 2/05/2016 3:15 pm, Jesse Mazer wrote:
On Mon, May 2, 2016 at 12:13 AM, Bruce Kellett
<[email protected] <mailto:[email protected]>> wrote:
No, I disagree. The setting *b* has no effect on what happens at
a remote location is sufficiently precise to encapsulate exactly
what physicists mean by locality. In quantum field theory, this
is generalized to the notion of local causality, which is the
statement that the commutators of all spacelike separate
variables vanish -- as you mention below.
And if you used full quantum description of the measuring apparatus
and experimenter, and didn't assume any collapse on measurement,
then there would in general be no single "setting b" in the region
of spacetime where one experimenter was choosing a setting, but
rather a superposition of different settings. Do you think your
preferred definition can be meaningfully applied to this case, and
if so how?
I do not know what you here mean by "collapse on measurement"? It
seems that you might be confusing a collapse to a single world after
measurement with the projection postulate of standard quantum theory.
The projection postulate is essential if one is to get stable
physical results -- repeated openings of the box in Schrödinger's cat
experiments would result in oscillations between dead and alive cats.
The projection postulate is replaced by the FPI in Everett, and as I
explained yesterday, it is just self-entanglement, or what I call
often the contagion of superposition:
Alice * (up + down) = Alice * up + Alice * down.
If Alice look, as many times as she want at the up/down state of the
particle, she will find up (and always up) *and* down and always down.
The reason is that once she find up, Alice becomes Alice-up, and that
state does no more factor out the particle state (unless memory erasure).
That is just the projection postulate, it cannot be replaced if you want
to agree with observation. As I thought, you have confused this with the
collapse of the wave function to a single world. Unless you sort out
this confusion you will never understand quantum mechanics.
Bruce
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