Re: [Phys-L] Big Bang

[John Denker <jsd@av8n.com>]

On 03/14/2013 10:41 AM, Anthony Lapinski wrote:
> The Olbers' paradox idea. Since the night sky is dark, the universe must
> be finite with a finite number of stars.
>
> Or maybe this is not really valid/scientific?

It's not right.  It is a classic example of an argument that is
"almost" right but leads to completely the wrong conclusion.

First of all, the "dark" sky is not completely dark!  It's just not
very bright on the human scale.  It glows with a black-body temperature
of 2.7 kelvin.  This is the cosmic background radiation, and it is
everywhere for exactly the reason that Olbers pointed out.  That is,
if you look in an arbitrary direction, eventually your line of sight
will it /something/.

The only thing that Olbers missed was the expansion of the universe.
Eventually your line of sight will hit some primordial plasma or some
such ... but the "hit" corresponds to a long-ago time.  The color of
the cosmic background radiation is not white (the color of stars) but
rather far-far-infra-red, because it cooled as it expanded.