All of the universe we can see is made from matter of the kind we find near us, and in about the same abundances of the elements everywhere. Most of this matter is at the temperature of the surface of the Sun. There is also quite a lot, several percent, of cool matter often found in interstellar clouds. Then, we think there is a large reservoir of 'dark matter' which may not even be matter at all. Some astronomers believe this makes up anywhere from 20 to 99 percent the total 'mass' of the universe which ads up to about 30% of the critical density. If that is the case, the stars and galaxies we actually see in the sky are only a few percent of what the universe actually contains. The rest of the universe includes a cosmological constant 'dark energy' that pervades space and contributes about 70% to the critical density. It also causes the expansion of the universe to accelerate. The above diagram shows the amount of dark matter, Omega-M, compared to the cosmological constant, based on current observational limits shown by the red and blue curves. Only a small zone is at the common intersection of the two limits.
Oh yes, don't forget that the largest single constituent of the universe is 'empty' space. Physicists and astronomers are only now beginning to understand what space 'is'.
Copyright 1997 Dr. Sten Odenwald
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