On 12 Nov 2017, at 23:05, Bruce Kellett wrote:
On 13/11/2017 4:02 am, Brent Meeker wrote:
On 11/11/2017 10:57 PM, Bruce Kellett wrote:
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.
True? This is a hypothetical model. In Bruno's model there are
infinitely many worlds "by construction".
That is not what the formalism of the Schrödinger equation says.
According to the SE, the number of worlds is exactly equal to the
number of components in the superposition. These 'infinitely many'
worlds are a fantasy. Besides, they do absolutely nothing towards
explaining the violations of Bell's inequality.
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?
Exactly the problem with Bruno's model. He says it recovers things
like linearity and superposition - but beyond that it's not clear
that it can recover QM. He calls this "the white rabbit problem"
as though it will be confined to a few peculiarities.
Yes, that is the point I have been trying to make for a long time.
Bruno does not have a theory that eliminates non-locality by
appealing to many worlds. He just hopes that by claiming it often
enough people will come to believe it.
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.
No, Bruce, you're not getting. It your stuck in Everett/Dewitt
version of many worlds in which there is branching from one to two
to many. Imagine an ensemble of worlds which "splits" into two
ensembles when Alice makes her measurement.
Why should I imagine any such thing? That is not in the formalism of
the SE, that is not many worlds as widely understood. But even if
you imagine infinitely many ensembles of whatever you like, that
gets you no nearer to an explanation of the irreducible non-locality.
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.
I understand that. I just noted it as another no-collapse model.
Superdeterminism is a collapse model.
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.
Right. They haven't been shown not to exist, or even be rare, in
the plenum of Bruno's Everything Computable. It has been shown
empirically that we never experience one.
What really annoys me is the continued claim that many worlds
eliminates the need for non-locality. It does not, and neither Bruno
nor anyone else has ever produced a valid argument as to how many
worlds might restore locality.
But nobody has proved that there is non locality in the MWI. EPR-BELL
proves non-locality apparant in each branch, but the MWI avoids the
needs of action at a distance to explains them. Once Alice and Bob are
space-separated, their identity are independent. It makes no sense to
talk of each of them like if they were related, (unless you correlate
them with a third observer, etc) If they do measurement, some God
could see that they are indeed no more related, but if they decide to
come back to place where they can compared locally their spin, they
will always get contact to the corresponding observer with the well
correlated spin. The independent Alice and Bob will never meet because
they can't belong to the same branch of the multiverse, by the MWI of
the singlet state. So Mitra is right. Although Bertlmann's socks are
tyically not working for Bell's violation in a MONO-universe, it works
again in the MWI, applied in this case to the whole singlet state.
Bruno
Bruce
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