🚀 go-pugleaf

In article <1992Apr8.071015.17512@ifi.uio.no> jarlo@ifi.uio.no (Jarl Magne  
Michael stensen) writes:
> I would want to ask all of you this wery simple (?) question: what is time?

I'm not sure whether you realize this, but you are asking one of the biggest
questions in physics these days. Answering this satisfactorily would
lead (it is hoped) to understanding many of the unresolved issues in
quantizing gravity.
 
> Let me first try to recap the basic knowledge and ideas in physics today 
> about this subject. 
> 
> First of all, time is not absolute. At least this is what SR and GR states. 
> There is no absolute past and present, or absolute clock ticking somewhere in
> the heavens.
> Newton assumed this to be correct, after all muons and other strange beasts
> did not run around with big signs on them in his time either. But today we
> safely (?) assume that there is no absolute time.

It depends what you mean by absolute time. If we define spatial 3-surfaces
in the universe to be at constant time if they are homogeneous and isotropic
(which is standard in classical cosmology) then one can define a preferred
universal time. This is because the cosmic background radiation essentially
gives us a preferred frame.
 
> Time is closely related to the curvature of space and thus is a geometrical
> object. We know that the picture of the slowing of relative time in a strong
> gravitational well relates to the "dip" in space at the point. (In pictures)

This is true, but I think it does not address the point properly. Specifically,
the entire 4-D space-time bends when matter/energy is present. Thus, time
*and* space are altered. The real question (in my opinion) is why is one
of these 4 dimensions, time, singled out by other dynamical laws (as expressed
in the metric signature).
  
> Is it impossible that time could NOT be continous?

It would require a drastic change in our understanding of physics 
(especially quantum mechanics). I believe that a discretized time would
not allow for a discrete energy spectrum under that theory. Since we have
observed discrete energy spectra, there is certainly a large price to pay
for postulating discrete time.
 
--
########################## _`|'_ ##############################################
##  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)      ##