From the reference in this answer I learned that our current estimate for the density parameter (i.e., the density of the universe divided by the critical density, which determines the shape of the universe) is 0.9993 +/- 0.0019. But I’m also interested in the history: how our estimates of this parameter have changed since the first attempts at measuring it were made.

I have tried to find this information myself, and once again I have failed. Can anyone please help me?

I don’t need a complete year-by-year account – a few historical highlights will do. (But I do need sources.)

I have also asked this question on Physics StackExchange, but there have been no responses. I suppose this is a better forum to ask.


I found an article by Wendy L. Freedman Determination of cosmological parameters which contained the following graphics

Density over time

The corresponding references should be listed in the references of that paper


  • The online article is also published as Invited Review given at the Nobel Symposium, Particle Physics and the Universe, Haga Slott, Sweden, August, 1998. Published in Physica Scripta, Vol. T85, 37-46, 2000.
  • http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/denpar.html offers a value of 1.02 +/- 0.02 and dates back to the 2000s
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    $\begingroup$ I need help understanding the first reference. I'm interested in $\Omega$, but this reference is only about estimates of $\Omega_m$, which is just one component of $\Omega$. Were the other components assumed to be 0 or near-0 at the time? And if so, did they really think that the universe is strongly hyperbolic? Or did they realize that they were missing something? (The other reference was very useful, thanks!) $\endgroup$ – Casper Jan 27 at 21:07
  • $\begingroup$ @Casper Maybe you want to ask a follow-up question? This aside: Have you seen ned.ipac.caltech.edu/level5/Freedman2/Freed7.html and what it says about an Einstein-de Sitter universe? The latter Wikipedia link also makes some historical remarks, e.g. archive.org/details/cosmologycontrov00helg $\endgroup$ – B--rian Jan 27 at 21:14

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