Re: Cosmology

[Leigh Palmer <palmer@SFU.CA>]

> Leigh Palmer wrote:
>
> >  There is no evidence that our galaxy is expanding. The universe is
> >  expanding according to evidence of a couple of kinds, but none of
> >  that evidence arises from observation of objects within our galaxy.
> >  No external galaxy is seen to be expanding, either.
>
> I am by no means a cosmologist, but I do enjoy reading and thinking about such
> things.  I think I understand why you are saying that the evidence of the
> expansion of our universe is not found within our galaxy or by observation of
> other galaxies.  I wonder though why you would so definitively state that our
> galaxy is not expanding.  If the Milky Way was expanding at a rate similar to
> that observed in the universe at large would we have techniques capable of
> measure this expansion on scales as small as our galaxy?  Perhaps I am missing
> something obvious.

You make me figure out Hubble's constant in unreasonable units.

           75 km/s/Mpc                -18  -1           -11   -1
       ------------------- = 2.43 x 10    s   = 7.7 x 10   yr
        31 x 10^18 km/Mpc

Ah! Hubble's constant can be expressed in parts per trillion per annum,
and the number comes out to be almost the same. (Please, someone check
my arithmetic. That's such a neat result that it ought to be better
known.)

It is clear that the astronomical unit is known to about 130 parts per
trillion, and if the solar system were expanding at the Hubble rate it
would be evident in two years' time. Since measurements of the AU go
back much longer than two years with high precision, expansion of the
solar system would have been seen by now. I'm afraid I can't suggest
high precision measurements on a larger scale than this.

I rest my case, but I'd be grateful for someone to check my arithmetic.

Leigh