🚀 go-pugleaf

Where did all these physical philosophers come from all of a sudden?

In article <1992Apr9.023836.13990@csl.sri.com> ronnie@cisco.com (Ronnie B. Kon)  
writes:
> Consider a section of space-time which contains a perfect vacuum.

Section usually has a special meaning in space-time physics, but I assume
you mean a 4-D subset (maybe "chunk" would be good).

>  What is the space-time?

Mathematically, it is a 4-dimensional curved space. Physically, it is an
"arena" in which physical processes can take place.

>  Does it have temperature (3 degrees K)?

Depends what you mean by a vacuum. If it is classical and empty (neither of
which are likely to be true for chunks of space-time as we know it) then the
answer must be know (no energy --> no 3K photons). If you mean a chunk with
no massive particles (which is not possible even in the semi-classical limit)
then the photons in it at least have a 3K temperature. If you want even a
semi-classical (lowest order quantum effects) space-time, then you are 
beyond my ability to say (maybe some other's out there know).

>  How does it exist?

You'll have to be more specific.

>  It must be curved (in a relatavistic universe) so there must 
> be something to be curved. But if there is something, it must be 
> constructed of particles, so it can't be a vacuum. Or is space-time
> not constructed of particles? 

In classical space-time, space-time is not built out of particles. It simply
gives particles someplace to be (pardon the handwaving). It's existence is
seperate from the existence of particles.

> If not, what can it be constructed of? 

This is a pretty ambiguous question. What is matter constructed of? What is
energy constructed of? What is an electric field constructed of? These are
not questions that we can ask meaningfully at this point in physics.
 
> Will space-time and matter be unified one day?  (No, I don't expect a
> definitive yes.  Maybe a definitive no though).

I'll give you a definitive "perhaps" :-).

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########################## _`|'_ ##############################################
##  Warren G. Anderson     |o o| "... for its truth does not matter, and is  ##
##  Dept. of Physics       ( ^ )  unimaginable." -J. Ashbery, The New Spirit ##
##  University of Alberta  /\-/\      (anderson@fermi.phys.ualberta.ca)      ##