Darren New <dne### [at] sanrrcom> wrote:
> 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.

  It still states that the entropy of an isolated system never decreases.

> > 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.

  That would mean that entropy is also reversible, which would break the
second law.

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

  The sourced wikipedia text seems to disagree with that assessment.

"For isolated systems, entropy never decreases. This fact has several
important consequences in science: first, it prohibits "perpetual
motion" machines; and second, it suggests an arrow of time. Increases
in entropy correspond to irreversible changes in a system, because
some energy must be expended as waste heat, limiting the amount of
work a system can do."

> >   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 does that change the claim "space must exist"?

  If you accept the Pauli exclusion principle as one of the fundamental
laws of nature, then you have to accept space existing (or explain the
law in question in the case that space does not really exist).

> >   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.

  Even if spacetime couldn't exist without energy, does that mean that
spacetime *is* energy?

-- 
                                                          - Warp

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