Re: Universe topology

Michael S. wrote:

>What does it mean when people speak of the universe's topology? Does this
>topology imply any type of large scale variation in the universe's
>fundamental physical constants?
>
>-- Michael S.
>  
>
  No, it does not assume any variations in the fundamental constants.
It is essentially a way of describing in how many ways you draw a
straight line from point A that eventually hits point A again.  Let
me give you a few examples.  In the most trivial form of a flat
universe, the universe will behave like an infinitely large flat
sheet of paper.  You let the line start at point A, and it will never
come back to point A, but if you take your sheet of paper, and roll
it into a cylinder there is exactly one straight line starting at A
that will hit A from the other side after having gone one turn
around the cylinder.  Now you can take the cylinder and glue its
ends together to get a torus, and then there are two different
kinds of lines that will close at A, and you can also find
straight lines that are combinations of these two kinds of lines.
On a sphere things are a bit different again, and there is only
one kind of "straight lines", great circles, but on the other
hand all the lines that start at A will return to A after one
round around the circles.  These are just some of the simplest
examples of the possible topologies of the universe.  There
is a good article on this in Scientific American, April 1999,
I believe.

Ulf Torkelsson