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Posted by Ken S. Tucker on January 19, 2008, 1:31 pm
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On Jan 18, 2:12 pm, david.willi...@bayman.org (David Williams) wrote:
> -> If when we see the blackness of the night time sky we are in fact seeing
> -> dust,
> -> then there is surely enough matter in the universe to block us from seeing
> -> the distant galaxies.
>
> -> But there is not.
>
> I tried to give the answer that is generally accepted by astronomers a
> few days ago, but nobody took any notice...
>
> If the universe were infinite in extent, and filled with stars,
> galaxies, etc., with an averge density that is constant with distance,
> and if it were not expanding, then the sky would be brilliantly bright.
> The brightness of each star would be inversely proportional to the
> square of its distance, but the number of stars at any given distance
> would be proportional to the square of the distance. So the effects
> would cancel out, and each "shell" of stars at any given distance from
> us would contribute equally to the brightness of the sky. Since there's
> an infinite number of shells, the sky would be as bright as the surface
> of a star.
>
> This is called "Olbers paradox", after the guy who first described it,
> centuries ago.
>
> Dust, etc., in intergalactic space would make no difference! The dust
> would absorb energy until it is hot enough to radiate energy as fast as
> it receives it, at which point it would be as bright as the brilliant
> sky around it.
>
> The solution, according to all astronomers nowadays, is based on the
> expansion of the universe. Light from distant galaxies is redshifted,
> which makes them less bright than they would be without the redshift.
> Beyond about 12 billion light-years, the redshift is complete, and
> galaxies further away than that cannot be seen. So the *observable*
> universe is not infinite, so Olbers paradox does not apply.
> dow
There's something I find strange about Olber's paradox.
Let me lay out a 3D XYZ cartesian grid, with arbitrary
units of 1 mile, and at each vertex let there be a person.
Now I'll send out a light signal from the origin spreading
to all persons, at which time they each begin humming a
tune, generating a faint sound. (We'll assume sound
is carried by the medium).
Now according to Olber, the amplitude of the humming
will build indefinitely, in fact to infinity.
See the problem, the sound energy generated is every
where of finite density, i.e. 1 hummer/cubic mile, yet
the sound becomes infinitely dense.
Is there something wrong with that?
Regards
Ken S. Tucker
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