On 1/7/2014 1:35 PM, LizR wrote:
On 8 January 2014 08:59, Jesse Mazer <laserma...@gmail.com
<mailto: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. :-)
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.
Brent
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to everything-list+unsubscr...@googlegroups.com.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at http://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/groups/opt_out.
