On 22/04/2016 5:17 am, Jesse Mazer wrote:
On Wed, Apr 20, 2016 at 7:51 PM, Bruce Kellett
<[email protected] <mailto:[email protected]>> wrote:
On 21/04/2016 1:34 am, Jesse Mazer wrote:
On Tue, Apr 19, 2016 at 8:54 PM, Bruce Kellett
<[email protected] <mailto:[email protected]>>
wrote:
So, the fact that these simulated results were supposed to
have come from an entangled singlet pair has not been used
anywhere in your simulation. It has only ever been used to
link the copies of Alice and Bob, the statistics that they
observe come entirely from what you happen to put in you
accumulator for each setting of the relative orientations.
Saying the idea of a singlet pair "has not been used anywhere in
your simulation" and then saying it has "been used to link the
copies of Alice and Bob" seems like a contradiction--isn't the
linking itself part of the simulation?
No, there is no contradiction. You have used the fact that they
are measuring parts of an entangled system only to link the sets
of results. Nowhere have you used the quantum properties of the
entangled singlet pair in the simulation to calculate the
probabilities: you have imposed those probabilities from outside
by fiat.
Sure, it's a toy model so I just tailor it to give the correct
statistics for a single type of quantum experiment. But if I were to
try to do the same thing in a scheme where there *weren't* multiple
copies of Alice and Bob, so that each had to get a unique result *at
the place and time they make a measurement* (not just later when they
compare results), then Bell's theorem absolutely rules out doing this
in any classical setup that respects locality, even toy models. So,
the toy model is just mean to illustrate the principle that Bell's
theorem isn't applicable to situations where measurements don't yield
unique outcomes but just yield a bunch of different copies of a system
at a given location in space at a given time.
interesting. So you agree that you just feed in the statistics that you
want to come out -- they do not come from any principle physics that
your computers simulate. But each particular Alice and Bob we might
consider has to get a unique result for an experiment that they perform.
I am glad you agree that if you consider the actual physical situation,
locality is ruled out by the observed statistics. The fact that a
measurement might yield one of a series of different results does not
alter the fact that, in the multiworlds picture, there is only one
result in each possible branch. That is all I have ever claimed, and all
that is required for my conceptual argument to go through completely.
Once you accept this general principle, you can see that Bell's
theorem doesn't offer any fundamental obstacle to reformulating the
general laws of quantum mechanics in a way that yields the same
predictions about *all* observations using purely local equations, of
the kind that could be simulated on a computer where you have a bunch
of separate computers calculating how physical variables are evolving
in a confined region of space, and each computer can only get data
from other computers representing neighboring regions, in a
locality-respecting way. As I said, my reading of the non-mathematical
parts of Mark Rubin's paper suggests that the paper is coming up with
exactly such a model, albeit one that is only equivalent to a
non-relativistic quantum field theory (perhaps the math of doing it
for a relativistic field theory would be more difficult).
If you mean that you can recover locality for measurements on entangled
pairs in this way, then you have a different theory which is not
consistent with quantum mechanics.
You seem to be saying this is impossible in principle, and you're
confident enough of this to dismiss the possibility Rubin's paper has
done this without apparently understanding the mathematical details
either. So, given what I said above, should I take this to mean you
think you have an argument for the impossibility which is entirely
independent of Bell's theorem? If so you could you try to spell it out
in a more detailed, step-by-step way?
I have done this in the thread with smitra. The min conceptual argument
is contained in the humorous little scenario I devised:
I dream of some "XKCD-style" cartoon. Alice and Bob perform their
experiments with particular settings and get particular results, which
they separately record in lab books. Several weeks later, they meet up
in a cafe down the street for a coffee. Alice puts her lab book with her
results on the table, "Look", she says, "I got |+> with my magnet set at
zero degrees to our agreed reference orientation." There is a
pause.......then Bob slowly lays out his lab book. "Holy shit!", he
says, "I also got |+> at zero degrees to our agreed reference." They
look at each other with gradually increasing dismay........ "Fuck!",
they say in unison. "That means that we don't exist..........." Their
voices fade into silence, and then...........Nothing!.
The point here is that some combinations of results are forbidden. How
can this happen? Following back the train of information exchange
between the participants, and accepting that worlds, once decohered,
cannot suddenly disappear, it becomes apparent that the zero probability
branches cannot arise because they are forbidden at the stage when A and
B are still at spacelike separations. So they are forbidden non-locally.
That is all that is required to demonstrate that MWI does not remove
non-locality from quantum mechanics.
Bruce
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