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szajtan w poczta.onet.pl
Śro, 29 Paź 2003, 13:21:43 CET
> 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
why not ?
event horizon accounts for all evolution of expantion according to assumed
model. if it's less than the curent curvature radius then we won't see the
probe, if it's bigger we mae but not must see it, for the curvature
radius is changing in time.
> "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".
last time I checked the page expired so don't know what was there, but did
anyone said something about the relation of the event horizon to the
curvature ratius.? (this should be calculated)
> This is true even when \Omega_\Lambda = 0 - the Big Crunch happens
> before we can see the back of our head.
even better - another reason for which we will never see the sent signal
(probe), but with CDM=.3 and DE=.7 or anything close to it we have no big
crunch at all.
> > 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.
the fundamental nature of the model is that going in space we also move in
time. eg. Imagine that that space is closed, and expands slow enough that
a photon emited from your flashlight can round it, but as the time passes
expansion rate mae grow up, event horizon falls, (say cosmological
constant starts dominate) and the photon won't make it eventually.
> If you can think of an alternative model which only models our past
> time cone, fine.
if the accurate model predict things in the past, I see no reason why
it should not predict also things in the future.
below this this point I don't follow ;)
> 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
gash, does it says about CMB fluctuations ?
meaybe I should review the bible instead of Peebles, etc :)
> 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.
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