prosba o komentarz

[Boud Roukema]

On Tue, 28 Oct 2003, szajtan odwieczny wrote:

> What I think we can say for sure is that, although we're not sure about
> the actual curvature of our obserwable universe, and thus we're not sure
> if the space go on and on to infinity, it seems that it's quite sure that
> our universe is accelerating (q<0), and from this point of view we can say
> that if we send out a probe into the space even at the velocity of light,
> it's likely that it will never return regardelss of the the curvature
> of the universe, because it just won't overpass the expantion rate of the
> universe unless there is some nontrivial topology involved. The Big Crunch
> never happens in area where q<0 on Omega_l, Omega_m plane. So from our
> point of view we can say the spacetime is infinite if we're thinking in a

We can't say "the spacetime is infinite". What you mean is
"the http://www.wikipedia.org/wiki/Event_horizon is less than
2 \pi times the radius of curvature even if comoving space is a hypersphere".

This is true even when \Omega_\Lambda = 0   - the Big Crunch happens
before we can see the back of our head.

> way of traveling in it. If we think just of a space as a slice in some
> moment of time the quiestion is still open, but what is use of thinking

i think you mean here "in some spatial section at constant cosmological time".

> about space this way - it just cannot be separated from time right ?

It's the fundamental nature of the model, so we ought to think about it.

If you can think of an alternative model which only models our past
time cone, fine.  But personally this reminds me of the Christian
fundamentalist cosmology model where the Unvierse is only 6000 years
old, as written in the Bible.

It's a model which perfectly fits all cosmological observations,
including those of WMAP. ;) The Universe in this model is the inside
of a sphere of radius 6000 light-years, on which EM radiation of all
sorts of wavelengths (and we could add other particles) was generated
6000 years ago on this surface, emitted in the direction of the Sun
(and it continues to be generated) in such a way to reproduce a
"naive" model that makes it (more or less) easy for human beings to
interpret these in terms of simple laws of physics. The being "God/Bóg"
which generates the emission wants human beings to have an easily
interpretable Universe, he/she/it is extremely intelligent and able
to generate such complex emission patterns of radiation. Just like
he/she/it set up species of animals 6000 years ago in a way that
makes biologists think there must have been lots of evolution...

Personally i find the model ridiculous, but it perfectly fits all the
observations and avoids "extrapolation" into times with which we have
no written contact (prehistorical), and the Universe is only 6000
years old.

pozd
boud