On 4/21/2018 9:45 PM, smitra wrote:
On 22-04-2018 06:08, Brent Meeker wrote:
On 4/21/2018 8:39 PM, smitra wrote:
On 22-04-2018 02:05, Brent Meeker wrote:
On 4/21/2018 4:45 PM, smitra wrote:
Yes, collapse does imply non-locality, but note that in the MWI
there is no collapse. There is no real "splitting of Worlds" in
the MWI either, it's only an effective splitting that can be
interpreted as an effective collapse as observed in the various
effective worlds.
And that observation is predicted by events spacelike separated
from it.
Brent
And that ability for Alice to predict what Bob will find, poses a
problem for single world collapse theories. Only there does new
information appear after a measurement and that then happens in a
non-local way when making certain measurements on entangled pairs of
particles.
There are only four cases without collapse and in every case Alice can
predict Bob's result. The very fact, which you have brought up, that
any hidden variable theory that explains the results must be non-local
(like Bohmian QM) shows that effect is non-local.
Brent
In case of a collapse theory, the non-local effect is far more
problematic. Alice then finds a result at her place and because there
is no other copy of her who found the other result, new information
has appeared. And that means that Bob's result is now also well
defined but the information about his measurement exists at a
space-like separation. In the MWI Bob may know that Alice has already
made her measurement, but he would also know that Alice exists as a
superposition of two copies who will have found two different results,
I'm not sure what version of EPR you're assuming, but the copies of
Alice that exist (modulo decoherence) are dependent on Bob's (and vice
versa) result and this dependence is realized spacelike. Certain worlds
contain incompatible results and do not appear, i.e. are zeroed out in
the density matrix. This could be regarded as merely a consequence of
common cause, the initial net zero spin, but Bell's inequality shows
that assigning any definite spin to one of the particles is inconsistent
with the set of worlds realized. Of course you can follow t'Hooft's
solution, which is to suppose a common cause also for the choice of
measurement axes by Alice and Bob.
Brent
so there exists no information about what he is about to find later
when he will measure his spin at the distant location where Alice is
as that entire place is in a superposition.
Saibal
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