Hi Bruce,
Sorry I have been busy in March and lost track of some post(s).
On 06 Mar 2016, at 23:16, Bruce Kellett wrote:
On 7/03/2016 4:52 am, Bruno Marchal wrote:
On 04 Mar 2016, at 23:12, Brent Meeker wrote:
When Everett proposed QM without collapse many people were
attracted to it just because it was deterministic.
That is a motivation enough, but as I have explained, and is not to
badly explained in the book by Susskind and Friedman (except that
you have to read many pages before getting the quasi-answer) it
restores full locality.
This is a claim that is frequently made -- you yourself, Bruno, have
made it several times. But I think the claim is false. The general
consensus these days is that QM is irreducibly non-local. If you
have an argument that purports to show that Everettian MWI restores
locality, then produce it.
As I said, this is well done in the book by Susskind and Friedman, but
see also the explanation in the Everett FAQ of Price. You can also
read Deutsch and Hayden, or Tipler, who wrote papers on this topic.
The general consensus that QM is not local applies to QM+collapse, or
QM+one-world. We know that this needs spooky action at a distance
since Einstein Podolski Rosen. Bell made this clear and testable, but
he assumes counterfactual definiteness, which is not the case in the
many world.
The simplest reason why QM-without-collapse is that the equation are
linear differential equation. Susskind argues on this by showing that
the density matrix of Bob remains unchanged when Alice makes his
measurement. I once verify this for the case of teleportation.
And give the argument yourself -- do not take the lazy route of
referring to papers of dubious reliability.
Just read Everett himself. You are the one making the extraordinary
claim. I have not yet seen one proof that QM (without collapse)
entails non-locality. It entails only an apparent non-locality due to
our abstraction of the macro-superposition we are in.
To be sure, with computationalism this is an open problem, but if
there is non locality, it will need the first order modal logic of the
observable to be shown. Up to now, as far as we know, the comp
observable obeys the same quantum logic than QM, and it entails non-
locality only if we assume counterfactual definiteness, it seems to
me. I think that Price explanation is rather clear. If you think he
made some error, please show it to me.
Bruno
Bruce
Just to be unique, we have to invent two very weird mysterious
things: events without cause, and spooky action at a distance. It
seems obvious it is conceptually simpler to abandon the axiom "I am
unique", given that the theory explain where that illusion comes
from.
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