On 15 January 2014 06:11, John Clark <johnkcl...@gmail.com> wrote:

> On Sun, Jan 12, 2014 at 6:41 PM, LizR <lizj...@gmail.com> wrote:
>>  >>> "Retro-causality" (time symmetry is a better term) only exists at
>>>> the quantum level.
>>> >> Why? Where is the dividing line? And with a Schrodinger's Cat type
>>> device a quantum event can easily be magnified to a macro-event as large as
>>> desired, you could connect it up to an H-bomb.
>> > The dividing line appears to be roughly where decoherence occurs.
>> Basically anything above a single quantum entity engaged in a carefully
>> controlled interaction is liable to get its time symmetric properties
>> washed out by interactions with other particles
> The nucleus of an atom is tiny even by atomic standards so it is certainly
> at the quantum level, and in its natural state of existing inside a huge
> chunk of irregular gyrating matter this tiny thing is constantly subject to
> the slings and arrows of outrageous fortune from an astronomical number
> of other clumsy atoms; and yet the half life of Bismuth 209 is 1.9 * 10^19
> years. Why?

Because that's how long it takes for the relevant particles to get over the
potential barrier. But this is irrelevant. Atomic nuclei are (probably)
already on the wrong side of the "entropy fence" in any case. They're bound
states which can only occur under certain special cirumstances, namely when
the universe expands and cools enough to allow them to form. And atomic
nuclei haven't been used to violate Bell's inequality as far as I know.

 >> It's just a fact, if time were symmetrical then you'd be just as good
>> at predicting the future as you are at remembering the past, so you'd know
>> the outcome of an experiment before you performed it just as well as you
>> remember setting up the apparatus. But this is not the way things are
>> because the second law exists. And the second law exists because of low
>> entropy initial conditions. And I don't know why there were low entropy
>> initial conditions.
> > OK. So the above statement of yours about predicting the future is still
> false,

Yes it's false, I don't think this will come as a great news flash but the
> truth is we're not as good at predicting the future as we are at
> remembering the past. And the reason we're not is that time is not
> symmetrical.

Except below the level of coarse graining at which entropy operates, that
is correct. And I never claimed otherwise. As I keep saying, I'm only
claiming this is relevant in special circumstances like EPR experiments.

> > To recap briefly -- the laws of physics are time symmetrical,
> Yes, the fundamental laws of physics, the ones we know anyway, seem to be
> time symmetrical. But that doesn't mean that time is symmetrical.

...is just words. Stop nitpicking. If the laws of physics are time
symmetrical, that has a potential influence on EPR experiments.

> > and most particle interactions are constrained by boundary conditions.
> Yes, and that is why time is NOT symmetrical.

Stop playing with words. The time symmetry of fundamental physics is there,
so it's perfectly valid to say time is symmetrical below the level of
coarse graining needed to derive the 2nd law, and asymmetrical above it.
(That's virtually a simple restatement of Boltzmann's H-theorem "for
dummies".) The point is that symmetrical time may become apparent in EPR
setups. You haven't yet given even a suggestion of a reason why it
wouldn't, just a load of hand waving about stuff that is IRRELEVANT to EPR
experiments, which are carefully prepared to avoid all the influences
you've mentioned.

Now how about discussing what I've actually claimed, that time symmetry of
physics could account for the special situation which has to be created to
obtain EPR results?

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