Big Bang call a cosmological hypothesis of the beginning of expansion of the Universe and dynamic change of space and time. The term "Big Bang" is used also for the description of an event which happened 15 billion years ago and gave rise to origin of the Universe.
Early Universe
According to this theory the Universe appeared in the form of a hot clot of superdense matter then it began to extend and cool down. At the very first stage of evolution the Universe was in a superdense state and represented a quark-glyuonnuyu plasma. If protons and neutrons faced and formed more heavy-nuclei, time of their existence was insignificant a little. At the following collision with any fast particle they at once broke up to elementary components.
About 1 billion years ago formation of galaxies began, at that moment the Universe began to bear a faint resemblance to what we can see now. Through 300 thousand years after the Big Bang it so cooled down that electrons began to be kept strongly by kernels owing to what there were stable atoms which did not break up at once after impact with other kernel.
Formation of particles
Formation of particles began as a result of expansion of the Universe. Its further cooling led to formation of kernels of helium which resulted from primary nucleosynthesis. From the moment of the Big Bang there had to pass about three minutes before the Universe cooled down, and energy of impact decreased so that particles began to form steady kernels. The first three minutes the Universe represented the heated sea of elementary particles. Primary education of kernels was continued very not for long, after the first three minutes of a particle move away from each other so that collisions between them became extremely rare. During this short period of primary nucleosynthesis there was a deuterium — heavy isotope of hydrogen which kernel contains one proton and one neutron. Along with a deuterium were formed: helium-3, helium-4 and insignificant amount of lithium-7. More and more heavy elements appeared at a stage of formation of stars.
After the Universe birth
Approximately through one hundred-thousandth fraction of a second from the beginning of origin of the Universe the quarks connected in elementary particles. From this point the Universe became the cooling-down sea of elementary particles. After this process which is called great association fundamental forces began. Then at the Universe there was energy corresponding to the maximum energy which can be received in modern accelerators. Later spasmodic inflationary expansion began, along with it antiparticles disappeared.