From: *Bruno Marchal* <marc...@ulb.ac.be <mailto:marc...@ulb.ac.be>>
On 9 Jul 2018, at 14:07, Bruce Kellett <bhkell...@optusnet.com.au
<mailto:bhkell...@optusnet.com.au>> wrote:
Sure, this is a property of the singlet state in standard QM, because
Alice's measurement collapses the state so that only the correlated
part is available to Bob. It is that part of the explanation that is
lacking in your account. You do not see any non-locality, basically
because you are assuming it with being aware of what you are doing.
Don't despair -- many other highly trained physicists do exactly the
same thing. But this does mean that you have not explained anything
-- you have simply assumed the result. The individual measurements of
Alice and Bob do influence each other, or else no correlation could
ever arise.
If there was a collapse? OK. But without collapse, the correlation are
just due to the fact that the singlet state put Alice and Bob in
infinities of branches, and only when they make a measurement they
know in which branches they are. Up-down + down-up is the same state
as up’-down +down’-up’. That is what you are not taking into account,
I think.
There are no infinities of branches. There are only two branches for
each measurement, when Alice and Bob can only ever get 'up' or 'down',
two possibilities on each measurement. After N trials, there are 2^N
possible histories for Alice and 2^N histories for Bob. There are no
infinities, and no branches are created for magnet orientations in which
no one made a measurement. In the words of Asher Peres: "Unperformed
experiments have no results." There are no counterfactuals, all that is
ever used is actual data obtained by actual experimenters. When they
make a measurement, they create the branching. Because the result of the
measurement is unknown to them beforehand (no superdeterminism), they
locate on either the up or down branch. There are no up' or down'
branches. You are just making this up.
Each copy of Alice has a unique history consisting of a sequence of up
and down results recorded in her lab book. Similarly for Bob. All of
these results were obtained in the /same branch/ of the ever-branching
Everettian tree. Each measurement splits a branch, but branches never
meet or recombine. So the Alice that meets a Bob over coffee after the N
trials is the Alice with one particular branching history. The Bob she
meets is necessarily in the same world, and he has a similar particular
branching history corresponding to just one world. There are 2^N such
meetings, each with unique branching histories. The wonder of the
singlet state is that for all these Alice/Bob meetings, comparison of
the data recorded in their lab books /always/ gives correlations that
agree with quantum theory and violate the Bell inequalities. This
mystery of many branches that always give the correct results is the
mystery that is to be explained. Introducing infinities of branches, and
infinities of measurements that were never made and therefore have no
results does not offer any explanation. In fact, it is just plain silly.
We only ever have data from experiments that were actually performed by
real people. There is no fantasy data, and no fantasy branches floating
around that have to be eliminated by some magic or the other. The magic
of the singlet state is that no results counter to quantum mechanics can
ever be generated. And this can only be explained non-locally. All other
attempts flounder on stupidities.
Bruce
--
You received this message because you are subscribed to the Google Groups
"Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to everything-list+unsubscr...@googlegroups.com.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
