Re: News: Physicists Predict the Death of Cosmology.

On 26 May, 02:22, 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.

That is resonable. Why odd?

Does the
reciprocal of the age of the universe place a lower bound on the Hubble
constant? My brain hurts.

I guess it does. If you assume things are flying apart but not
accelerating apart, then yes, the Hubble constant would have looked
bigger in the past. And if you don't assume that, then how would you
have an opinion on the age of the universe in the first place?

I don't see what point you are making about the original post. They
are saying that in the distant future, the most parsimonious and
rational cosmology would be different, which invites the question of
why we think we think we are doing ok at it - we may have come along
too late to see a crucial part of the action. Maybe there was a
clearly visible turtle up until the end of the Cambrian.

The article in the original post seems confused to me, but maybe I'm
confused. I didn't think the speed of light gets exceeded in any
meaningful sense. Rapidly receding objects become *effectively*
invisible as they get red-shifted down to DC. And of course, they may
not be accelerating away - that is the whole point of spending so much
money on dark matter research.

.

Relevant Pages

  • Re: News: Physicists Predict the Death of Cosmology.
    ... That's only in Special Relativity. ... The universe is 13.7 billion years old. ... "age in light years" as intended. ... since an observational horizon that exceeds the age of the universe ...
    (talk.origins)
  • Re: News: Physicists Predict the Death of Cosmology.
    ... velocities greater than c, for essentially the reasons Ritsjoena gives. ... The universe is 13.7 billion years old. ... since an observational horizon that exceeds the age of the universe ...
    (talk.origins)
  • Re: SR time dilation on remote objects ?
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    (sci.astro)
  • Re: Euclids postulates and non-Euclidean geometry
    ... |> Only if age was soley determined by the expansion. ... |> Despite what you say here the age of the universe has been determined ... |>>> Everything we can measure is recessing from everything else, ... synonyms RECEDE, RETREAT, RETRACT, BACK mean to move backward. ...
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  • Re: YEC
    ... radioactive elements so as to suggest an old Earth is not easy to ... only of great age but of the SAME great age (at least for those ... about absolutely everything in the universe shouting OLD AGE, ... would happen to one obscure biological entity on one obscure planet ...
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