ABSTRACT
During further expansion and cooling the universe had overcome the phase transitions in elementary particles system. The very early universe occurred to be enormously hot and elementary particles had energies higher than those currently accessible in particle accelerators on the earth. Approximately 10-35 s after the Planck epoch the phase transition triggered an exponential expansion of the universe called the “period of cosmic inflation” [3,4]. After the end of this period the building material for the universe comprised the quark-gluon plasma. With time the temperature fell down to the values when the next phase transition called bariogenesis occurred. At this stage the quarks and gluons fused into barions such as protons and neutrons. Thus, just at this stage the first ever known hydrogen species, namely, protons were born. Further cooling led to the next phase transition: formation of physical forces and elementary particles in its modern form. Then the epoch of nuclear synthesis came when protons fused with neutrons and formed the nuclei of deuterium, helium-4, and some other light isotopes. On further cooling and expansion of the universe the moment occurred when gravitation became the dominant force. Some 380,000 years after the Big Bang the temperature became so low that the appearance of hydrogen atoms became possible. Prior to this the processes of ionization of hydrogen atoms and recombination of protons and electrons were in equilibrium. With the formation of neutral hydrogen the decoupling of substance and radiation occurred and the cosmic microwave background was emitted. The color temperature of the decoupled radiation has continued to decrease ever since; now down to 2.725 K, its temperature will continue to drop as the universe expands. According to the Big Bang model, the radiation from the sky measured today comes from a spherical surface called the “surface of last scattering” [5]. Figure 1.1 shows the above-mentioned three stages of the universe evolution after the moment of the Big Bang. So, the hydrogen atoms appeared on the second stage whereas hydrogen atoms were formed only on the third stage, thus 380,000 years later than protons. Mother Nature celebrated the birth of Big Bang’s children, that is, hydrogen atoms, by emitting of cosmic microwave background that contained a sophisticated problem to solve for future generations
of researchers. After 13.7 billion years, this splendid problem was solved; in 1965, Arno Penzias and Robert Woodrow Wilson from Bell Telephone Laboratories registered the cosmic background and were awarded the Nobel Prize in physics in 1978.
