On 07 Jan 2014, at 22:54, meekerdb wrote:
On 1/7/2014 1:35 PM, LizR wrote:
On 8 January 2014 08:59, Jesse Mazer <laserma...@gmail.com> wrote:
Well, most physicists already agrees physics is time-symmetric
(well, CPT-symmetric, but the implications are the same for Bell's
inequality and thermodynamics),
Yes, they do, but it doesn't appear to be taken into account when
discussing Bell's inequality.
but I don't see how this alone can explain violations of the Bell
inequality.
No, you need to work out the consequences mathematically, and I
dare say that is quite difficult. This is simply a logical
demonstration that Bell's inequality can be violated while
retaining locality and realism, which is otherwise impossible.
To explain Bell inequality violations using a time-symmetric theory
like the one sketched out by Huw Price, you need to assume hidden
variables (the particles have predetermined spin states along all
axes the experimenters might choose to measure),
Yes, hence it retains realism. The variables are only "hidden" in
the sense that they can't be measured half way through the
experiment - e.g. by measuring the state of photons while in flight
- because any interference with the experiment would destroy the
correlations between the measuring apparatus and the emitter.
*and* you must further assume that the particle emitter that
creates the particles can "predict" what axes the experimenters
will choose to measure on each trial,
That's what time symmetry means. There is no "prediction" involved
in the sense you mean - the state of the measuring apparatus
affects the photons, just as the emitter does. (This can of course
be extended to a multiverse, with the measuring apparatus
simultaneously in various states which create a superposition of
emitters. But that isn't necessary.)
so that the statistics of what combinations of hidden variables get
created will depend on the experimenters' later choices. For
examples on trials where they are both going to measure along the x-
axis the emitter will always create particles that have opposite
spins along the x-axis, whereas on trials where the experimenters
both measure on some other axis, or where they each choose
different axes to measure, the emitter can create particle pairs
that don't have opposite spins on the x-axis. Is this the type of
solution you're thinking of?
Yes, that sounds about right. The particles' states throughout the
experiment are influenced by the measurement settings as well as by
the emitter that creates them. From that it follows logically that
information about particle A's measurement setting is available to
particle B at the point of its measurement, and vice versa.
(assuming the physics is local and realistic - the particles have
definite states throughout).
If so, it seems like this goes well beyond time-symmetry, since
time-symmetry doesn't normally allow for systems to contain
localized "records" of events in the future the way that they can
for events in the past (which presumably could be explained in
terms of the thermodynamic arrow of time caused by the universe
having a low-entropy past boundary condition but not a low-entropy
future boundary condition).
I'm afraid you've missed the point here, and then gone on to tie
yourself in knots. There is no thermodynamics or "sensitive
dependence on initial conditions" at the level of the individual
photons. Entropy is a statistical, high level outcome from a lot of
low-level time-reversible processes. Price assumes realism, that
the photons have a real state, with spins and so on, throughout the
experiment. Time symmetry simply says that this state is influenced
by boundary conditions at either end of its path - by the settings
of the measurement apparatus it encounters, and by the state of the
emitter. Since the photons are prepared so their states are
corellated ("entangled") this means that the state of photon A at
the point of emission influences the state of photon B (and vice
versa). If the relevant physics is time symmetric, then photon A's
state throughout the experiment is influenced by the state of
measuring device A. Hence the state of measuring device A affects
photon B, via the point at which they become entangled.
Which is what is observed in EPR experiments: the settings of
measurement device A affect the state of photon B.
I'll take this opportunity to agree completely with Liz's
explication above. :-)
Me too :-)
Notice too that if you take everything to be deterministic,
including the experimenter's choices of measurement you can violate
Bell's equality. So it just appears random to the experimenters
because they can't realize that their decisions were determined
where their past light cones overlapped. This is t'Hooft's
hyperdeterminism. It seems like taking the observed MWI branch and
making that the block universe, with all other branches not realized.
OK. That is why i think that the Cramer mono-world interpretation is
essentially a MWI + a selection principle, like Bohm theory, except it
uses forward weird conditions, which entails that hyperdeterminism.
Note that from a strict logical point of view, comp might still lead
also to a similar "unique physical reality", but there too, it asks
for a sort of number conspiracy of some sort. By default, many worlds
seems less demanding, both for QM, and even more in the
computationalist theory of mind.
Bruno
Brent
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