From: *Bruno Marchal* <[email protected] <mailto:[email protected]>>
On 6 Jul 2018, at 20:52, Brent Meeker <[email protected]
<mailto:[email protected]>> wrote:
On 7/6/2018 9:26 AM, Bruno Marchal wrote:
It is like they find themselves in the relevant partition of the
mutilverse, but as there has not been any collapse, nothing has
needed to propagate after than light. The non-locality, or better
inseparability, just assures that whatever differentiation will
occur locally, they will have the correlated spin, but at no point
are we assured that Alice meet something like the original Bob. The
differentiation of the universe develops locally.
No, it differentiates in a coordinated, space-like way, keeping
*/that Alice /*with /*that Bob*/ so that only the correctly
correlated Alice and Bob can meet, i.e. be in the same world at the
same time and place.
?
That my point. But that is why we don’t need FTL influence. In the
multiverse, they remains the same, but the inequality of Bells assured
them of not knowing in which branch they are.
Brent's comment is a misleading way to put it. There are no multiple
copies of Alice and Bob that do not have the correct correlations and
have to be eliminated. Every Alice copy meets every Bob copy, and they
all have the correct correlations. It is explaining how this happens
that is the whole point of the exercise. This can only happen if the
probability that any Bob copy gets 'up' when Alice gets 'up', or the
probabilities of any of the other three possible combinations, are all
correct. Getting these probabilities correct requires non-local
knowledge of the relative polarizer angles. If you don't understand
this, then you have not understood the basic quantum mechanics.
Once Alice and Bob are space-light separated, they will never meet
again after they made local measurement.
But they do meet again. Only events are space-like separated.
People have persistent world-lines which are both space-like and
time-like depending on the events chosen. But "meeting", being at
the same events, is invariant.
Each will meet only the corresponding (correlated) person, but there
is no reason we can identify them in any single word.
You can identify whomever meets as being in a single world. That's
the point of Bruce's exposition.
I am not sure I see your or Bruce point. I am not sure which Alice and
Bob you are talking about, nor if what you say would entail any FTL in
a single world. Entanglement just correlate infinities of Alice with
infinities of Bob. There is no notion of one Bob, once Alice and Bob
are separated by a sufficiently great distance.
There are no infinities of Alice or Bob. There are no such infinities in
quantum mechanics, or in the Schrödinger equation. Once you set a base,
there are only two copies of each experimenter. And the base is set by
choosing what to measure. Once that choice is made, the other possible
bases drop out of consideration. When Alice and Bob meet, they are in
the one world, even if there are four possible such meetings. You then
follow back according to the sequences of observations recorded in their
lab books -- this is exactly like the W/M duplication experiment. So you
follow back a particular world line -- there is no ambiguity.
May be you could elaborate. You believe that physical single world -
FTL influence exist? I think you will need more than a violation of
Bell inquiry for this.
There is no FTL signalling, and that is all that is required for Lorentz
invariance. Adding extra requirements is your fantasy, not physics.
Bruce
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