Research concerning the matter in the universe indicates the presence of non-luminous matter, and also non-baryonic matter (that is, matter not made up of quarks), which is called black or dark matter. This dark matter was predicted based on the properties of gravitation. Each body, in effect, creates a gravitational field, and undergoes the influences of all the other bodies. By studying the movement of a body it is possible to calculate its gravitational field, and also to localize and calculate the size of masses that create this field. Since 1933 (the work of Zwicky) many galaxies have been observed that contain stars whose rotational speed is not what theory says it should be: their rotation is too fast to maintain itself in those galaxies. The only explanation is that there is some matter (which must be much larger than the mass of the galaxies themselves) that is influencing those stars, and preventing centrifugal force from scattering them far from the center of their galaxies. This matter must be made up of electrically neutral elements, because it does not emit radiation. Hence the name, dark matter.

Dark matter constitutes about 23% of the total amount of matter in the universe. Baryonic matter (of which we ourselves, and the planets, and the “visible” stars are composed) represents only 4.5% of the total amount of matter in the universe. All the rest is dark energy (about 72%).