Re: News: Physicists Predict the Death of Cosmology.

On May 26, 3:22 am, Jim Willemin <jim***willemin@hot***mail.com>
wrote:
ZikZak <ZXBWDNKFY...@xxxxxxxxxxxxx> wrote in news:1180132365.533457.39260
@g4g2000hsf.googlegroups.com:



On May 25, 7:25 am, Greg Guarino <g...@xxxxxxxxxxxxx> wrote:
On Fri, 25 May 2007 10:42:58 GMT, Ye Old One <use...@xxxxxxxxx> wrote:

distant galaxies will eventually be moving
away faster than the speed of light.

I only got as far as general college physics. If memory serves, this
wasn't allowed, at least in the '70s,

Greg Guarino

That's only in Special Relativity. In General Relativity, two bodies
that are sufficiently far apart from each other can have relative
velocities greater than c, for essentially the reasons Ritsjoena gives.

I'm a little confused, I think. The universe is 13.7 billion years old.
The Hubble constant is something like 70 km/sec/megaparsec, I think. The
speed of light is 3e5 km/sec. That means that the observational limit of
the universe is 3e5/70 = 4300 megaparsecs (to the accuracy of these
figures) - things more than 4.3 gigaparsecs away are receeding at relative
velocities greater than c. 1 parsec = 3.26 light years, so the
observational horizon of the universe is 14 billion light years, give or
take... This is odd, but I'm not a cosmologist - has the observational
horizon always been the age of the universe in light years? It must have
been, since an observational horizon that exceeds the age of the universe
in light years would mean that we could see before the big bang. Does the
reciprocal of the age of the universe place a lower bound on the Hubble
constant? My brain hurts.

Yes size of the visible universe corresponds directly to its the age.
The further the distance the longer light needs to get here. So we
currently can look back until first light (=cosmic background
radiation) at the beginning of the universe.

.

Relevant Pages

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  • Re: News: Physicists Predict the Death of Cosmology.
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    (talk.origins)
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