Warp wrote:
>   Time must exist, or else it would be impossible to postulate essential
> properties of physics such as the second law of thermodynamics. 

The second law is statistical.

> You can unambiguously distinguish if a closed system is going forward in
> time by measuring its entropy.)

No you can't, because time is reversible. Entropy is an artifact of measurement.

Take a deck of cards and shuffle it. How likely is the order of cards you 
just shuffled?  It's exactly the same as the likelihood that all the cards 
are in the canonical order (ace to king, sorted by spade, heart, club, 
diamond).  Entropy is a measurement of how interesting to us a particular 
arrangement of atoms is.  The fact that you can't get work out of random 
heat is simply saying that it's really, really unlikely for random heat to 
suddenly all go one direction.

Note that QM has no arrow of time. Reactions going forward are identical 
(altho inverted) to reactions going backwards.

Break a rack of pool balls. (I.e., start the game.) Suddenly, it's much less 
ordered. But if you could measure exactly where everything is at the end and 
how fast it was going before it stopped and exactly how much friction there 
was and etc, you could reverse that. (Modulo QM uncertainty, of course.)

>   Space must exist, or else it would be impossible to postulate essential
> properties of physics, such as the Pauli exclusion principle. 

The Pauli exclusion principle is not part of GR. It's part of QM. :-)

> (How could
> you state that two particles cannot be at the same *place* at the same
> time if the very concept of "place" wouldn't exist?)

It does in QM. That's the fundamental problem and tension preventing GR from 
being unified with QM.

The *concept* of place exists. It's just a question of whether it's 
something real or something that falls out of our math and "common sense".

>   Just because space and time are relative doesn't mean they don't exist.

Maybe I'm misinterpreting stuff like this:

http://math.ucr.edu/home/baez/background.html

It seems to be saying that GR says that space and time exist because matter 
and energy exist. You can't have space or time without energy to be 
experiencing them, just like you can't have sound without air to carry it.

-- 
Darren New, San Diego CA, USA (PST)
   Serving Suggestion:
     "Don't serve this any more. It's awful."

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