On 11/11/2017 6:47 PM, Bruce Kellett wrote:
On 12/11/2017 4:34 am, John Clark wrote:
On Fri, Nov 10, 2017 at 7:08 PM, Alan Grayson
<agrayson2...@gmail.com>wrote:
>>
That's not the measurement problem, its determining if how
and why observation effects things.
>
Not to split hairs, but why we get what we get in quantum
measurements, and how measurement outcomes come to be what they
are, are the same problem IMO.
The measurement problem is not the ability or inability to predict
exact outcomes,
the measurement problem is defining what is
and
what
is not a measurement and
finding the
minimum properties a system
must
have to be an observer. Nondeterminism is not a problem and there is
no inconsistency at all regardless of what turns out to be true
;
if some effects have no cause and true randomness exists then that's
just the way things are are
and
t
here is no resulting paradox and no question that needs answering.
The title of this thread is about the consistency of Quantum
Mechanics, but far more important than QM is the ability of ANY
theory to be compatible with experimental results, and one of those
experiments shows the violation of Bell's Inequality. And that
violation tells us that for ANY theory to be successful at explaining
how the world works AT LEAST one of the following properties of that
theory must be untrue:
1) Determinism
2) Locality
3) Realism
Is Many Worlds deterministic? Yes in the sense that it just follows
the wave function and that is deterministic, it's only the collapse
of the wave function that is nondeterministic and that never happens
in Manny Worlds.
Is Many Worlds Local? Some say yes but I would say no because those
other worlds are about as non-local as you can get, you can't get
there even with infinite time on your side. But even if I'm wrong
about locality Many Worlds would still be in the running for a
successful theory because it is certainly not realistic.
I would agree with you that the many worlds account is non-local. The
problem that MW faces is that the separate worlds split off when
measurements are made at either end of the EPR experiment must somehow
be made to match up appropriately when the two experimenters
communicate. This requires coordination of separate worlds, which, as
you say, is about as non-local as you can get.
The problem becomes particularly apparent if you consider an EPR
experiment with time-like separation. Let Alice prepare an EPR pair in
her laboratory, then measure the spin of one of the pair in some
defined direction. She then takes the other member of the EPR pair
down the corridor to her partner, Bob, and gets him to measure the
spin projection in the same direction. If the two particles are
independent, then both measurements give 50/50 chances for up/down.
After Alice measures her particle, she splits into Alice_up and Alice
_down according to her result. Both copies then go to Bob's
laboratory, which by then has also split according to Alice's result.
So Alice_up meets Bob, but when he measures his particle, he still has
50/50 chances of either result. Unfortunately, the only result that is
consistent with spin conservation is that if Alice got 'up', he must
get 'down', and vice verse (remember that the measurements are aligned
by design).
Since Alice_up can't meet a Bob_up, there must be a non-local
influence that determines Bob's result according to which Alice he
meets. This is not removed be assuming no collapse and many worlds.
But Bruno's model assumes infinitely many worlds; some in which Alice
sees up and Bob sees down and others in which Alice sees down and Bob
sees up..."influence" doesn't really appear in the model because it's
kind of block multiverse and there's some rule (conservation of angular
momentum) that means up-up and down-down don't appear. I think this is
also true of t'Hooft's super-deterministic model because in that model
there's nothing special about the event of Alice's measurement that
needs to be communicated. The idea of influence propagating from an
event derives from the idea that Alice had "free-will" and so her choice
had to be communicated from the measurement event.
Brent
Of course, with time-like separation, the results can be explained by
a local hidden variable, but no such explanation is available for
space-like separated measurements, and the same explanation must be
available for both cases. Since non-locality is still present for
time-like separations, it must be present in all cases. So many worlds
do not eliminate non-locality in Bell-pair measurements.
Bruce
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