Dense Space

Would anyone be able to tell me, or tell me where I could find, an
estimate for the density of the matter floating around in space 4 or
so billion years ago?

Thank you

Jack Goodfriend

In article ,
(Jack Goodfriend) writes:
Would anyone be able to tell me, or tell me where I could find, an
estimate for the density of the matter floating around in space 4 or
so billion years ago?

Are you looking for an average over the whole Universe or in some
particular type of local region?

For an average over the whole Universe, a bit of fooling with Ned
Wright's cosmology calculator
http://www.astro.ucla.edu/~wright/CosmoCalc.html
shows that 4 Gyr ago corresponds to redshift 0.37. Thus the average
matter density was (1.37)^3 times greater then than now, unless I'm
completely confused.

If you want some particular type of local regions, a good first guess
would be "same as now." 4 Gyr is just not all that long ago, and
physical conditions were not all that different back then.
Furthermore, a lot of region types (e.g., stars, molecular clouds,
ionized gas clouds) have densities controlled by fundamental physics,
and as far as we know, the laws of physics were the same then as now.
There has been a minor increase in heavy element abundance in the
last 4 Gyr, but it probably isn't enough to make much difference.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
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