andrel <a_l### [at] hotmailcom> wrote:
> I have apparently missed a lot since my physics study. I was under the 
> impression that the size of the universe is of the order of a sphere 
> with a radius of the age of the universe times the speed of light. Could 
> you give a pointer to those current theories that you mentioned?

  Glad you asked.

  It is, in fact, a rather common misconception that the theory of
relativity limits the speed at which the universe can expand (even
some scientists and cosmology papers hold this misconception).

  However, the theory of relativity does not limit the speed at which
the universe can expand. The distance between two points in the universe
can grow faster than c without it breaking relativity. The reason why
people get confused is that they tend to think that if the distance
between two points increases at a rate which is larger than c, that means
that the points are *moving* away from each other faster than c, thus
breaking relativity. However, the points are not moving. The space
geometry between them is changing (in very simplistic terms, new space
appears between them). This is summarized, for example, here:

http://en.wikipedia.org/wiki/Metric_expansion_of_space

"The metric expansion leads naturally to recession speeds which exceed
the "speed of light" c and to distances which exceed c times the age
of the universe, which is a frequent source of confusion among
amateurs and even professional physicists.[1] The speed c has no
special significance at cosmological scales."

  No information of any type whatsoever can be transferred by any means
between two points which are recessing faster than c. This is exactly
what causes the so-called cosmological horizon (stub article at
http://en.wikipedia.org/wiki/Cosmological_horizon )

  In fact, assuming that the borders of the universe had always grown
at a constant rate of c is against observation. Moreover, it has been
conjectured that the universe suffered an exponential inflation period
at its first moments, which would explain many observed phenomena. This
is an interesting article about the subject:

http://en.wikipedia.org/wiki/Cosmic_inflation

-- 
                                                          - Warp

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