Deuterium in the Universe and in interstellar molecules

Deuterium role in the elementary processes of the Universe is investigated. The deuterium was formed during the ''Great explosion''. The modern deuterium amount should not be higher than the amount of the initial deuterium. Deuterium is not found on the Sun and other stars as it burns quickly there. On the Earth 1 ton of sea water contains 17 g of deuterium. Cosmic rays contain 100 times more deuterium than the Earth, while in the atmospheres of giants this amount is 3 times lower. There is one deuterium atom per 50000 hydrogen atom in the interstellar gas. According to the data of observations on interstellar molecules, there is one deuterium atom per 10-1000 hydrogen atoms. However, measurements of interstellar molecules can not be as reliable estimates of the real amount of deuterium in the interstellar medium. Results of measuring the DI/HI ratio, obtained according to absorption lines of atomic hydrogen are most reliable. The deuterium amount measured can be used to determine the mean density of the Universe and, consequently, the law of its expansion. The mean density of the matter in the Universe determined according to the deuterium amount and that actually observed in galaxies can be considered coinciding in the first approximation