On 12/11/2017 5:39 pm, Brent Meeker wrote:
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.
That is simply not true. There are, by construction, only two worlds
in this scenario before Bob makes his measurment, and that splits him
(along with the Alice beside him) into two more.
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.
The world in which Alice and Bob both get an 'up' result does not
obey conservation of angular momentum. How do you exclude that world?
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.
You are not getting it, Brent! There is only one EPR pair made in
this scenario. Alice and Bob each measure their separate particles,
and get either up or down, with 50% each way. Once Alice has measured
and takes her 'up' result to Bob, he has to make a separate
measurement. According to AM conservation he can't get 'up' also (in
this world) since Alice has presented him with an 'up' result. What
prevents him getting 'up'? That is still a 50% chance, after all,
according to the wave function. The point of this scenario is that the
_only_ possibility for Bob after Alice brings him an 'up' result is
'down'. What stops the 'up' possibility for his measurement?
'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.
Superdeterminism is a red herring here. 't Hooft explicitly rejects
many words, so his arguments do not apply to the case I am presenting,
which is developed in an explicit no-collapse, many worlds context.
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.
If that means anything at all, it is still non-local because Bruno
has to rule out the worlds in which angular momentum is not conserved;
he has not shown how he can do this. If it is simply that you cannot
find yourself in a world in which AM is not conserved, then that is
just an unabashed appeal to magic, since such worlds have not been
shown not to exist.
Bruce
