On 11 January 2014 06:43, John Clark <johnkcl...@gmail.com> wrote:

> On Thu, Jan 9, 2014 at 5:38 PM, LizR <lizj...@gmail.com> wrote:
> >As a lot of people have now pointed out, physics can be local and
>> relistic if time symmetry is valid.
> If time is symmetrical then retro-causality exists, so how can realism
> hold? How can the outcome of a coin flip today have a definite value
> independent of the observer if next year or next millennium someone can
> cause a change in today's coin flip? If realism holds under those
> circumstances then the word "realism" has no meaning.

"Retro-causality" (time symmetry is a better term) only exists at the
quantum level. The laws of physics are time-symmetric, but constrained by
boundary conditions. There is a very influential boundary condition in what
we call the past, namely the Big Bang, plus less influential ones in the
future, like the settings of measuring apparatuses. At all scales except
that of individual quantum events, the pastward boundary condition washes
out any noticeable effects of time symmetry. (That's what it means when we
say that entropy increase involves coarse graining.)

> And by the way, if time is symmetrical then there is no point in ever
> actually performing an experiment because you would remember the future as
> clearly as you remember the past, so you would already remember the outcome
> of the experiment just as clearly as you remember setting up the
> experimental apparatus.

I assume you're not so stupid as to think that's what I've been claiming,
so I can only assume this is a deliberate attempt at mockery, directed at a
straw man as such attempts usually are. I had hoped for a better standard
of debate on this list.

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