On 28-Jul-08 23:27, Warp wrote:
> 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 
is it?
> (even
> some scientists and cosmology papers hold this misconception).

yup, this physicist for instance.

>   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. 

yup, but that has no additional implication for the speed at which the 
universe can expand.

> 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

yes, but as I said above that has no implication for the size of the 
universe.

> 
> "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

And what exactly does this all prove? I haven't seen anything in those 
links that I did not know (but I admit I did not read everything) and 
nothing that even remotely supports your 'The real size of the universe 
is completely impossible to know. It could be just slightly larger than 
the observable universe, or it could be staggeringly larger. There's 
just no way of knowing.' but I might have missed it.
Unless you are in a roundabout way referring to the problem that you can 
not define the 'now' for which you are computing the size.

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