How much dark matter is there in the Universe?
One parameter which allows us to decide upon the possible geometric
shape of the Universe and establish the ultimate destiny of the Universe is the average density of the matter present in the Universe.
Inflationary cosmological models predict a value of 1 for the Omega parameter, and a flat Universe. Given that, scientists deduce, from the visible quantity of matter, an Omega value of 0.005, we can say that dark matter should make up 99.5% of the mass of the Universe. But is it possible to verify that the density of matter really corresponds to the critical density, as foreseen in the theory of inflation?
The total amount of matter required in order to keep stars in galaxies and galaxies in superclusters is estimated to be 35% of that needed to obtain a Universe of euclidean geometry. It is also believed that this matter is subdivided as follows:
On the other hand, other studies (most recently the
WMAP experiment) have demonstrated that the small fluctuations in
temperature in the microwave
have the characteristics expected in the case of a Universe with an energy density equal to
the critical density.
So what is the remaining 65% of "density" which has nothing
to do with either visible matter or dark matter? We will look at this in the next section.