On 11/11/2017 9:56 PM, Bruce Kellett wrote:
On 12/11/2017 4:04 pm, Brent Meeker wrote:
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.
That does not address the scenario I have outlined. In the time-like
case, Alice_up meets Bob with a spin state that can result in either
up or down; similarly Alice_down meets Bob with a spin state on which
Bob's measurement can result in either up or down with 50% of each.
There are only two worlds involved at that stage.
No, that's the point. There are infinitely many "worlds" involved from
the beginning. There's no splitting. It's all predetermined.
The question is, how does Bob with Alice_up not get an up result,
contradicting conservation of angular momentum.
Because each world obeys conservation of angular momentum.
Similarly, how does Bob with Alice_down not get a down result. Since
the measurement axes are explicitly aligned in this case, the 'up-up'
and 'down-down' observations are forbidden. Appealing to an infinity
of worlds is not going to help.
They don't really need to be infinite, just very numerous so that when
we repeat some experiment for which the Born rule predicts 1/pi or other
irrational number, we won't get results in our finite number of tests
that are inconsistent with it.
't Hooft's superdeterministic model simply says that in this case the
particles are originally produced with spins in the previously agreed
measurement direction. In other words, the 'previously agreed'
direction was determined from the time of the big bang. Maudlin in his
Facebook discussion with 't Hooft makes it clear that he thinks this
is not a well-formulated position. It is not a matter of freedom of
the will in choosing setups and orientations, because these can be
chosen according to the digits of pi after the 10,000,000th.
They can only be chosen that way by physically computing and choosing
that number; events determined since the Big Bang.
Or anything else, and the initial conditions at the big bang could not
have covered all possibilities - at least not in any believable way.
But we can't test all possibilities. Alice and Bob can only do the
experiments determined by the past state of the universe, i.e. those
determined by the Big Bang. I don't know what's "unbelievable" about
that - it's what Laplace et al once believed about the world.
If many worlders are to explain the time-like case I have outlined,
they are going to have to work quite hard to avoid the notion of some
influence at a distance.
In Bruno's model the "influence at a distance" is determing which world
you're in.
Brent
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