How electrons began to remain in orbits
In the early hot universe, free electrons were being captured by protons, forming hydrogen atoms. The photons, emitted in this process called recombination, took away the difference between the summary mass of free particles and the mass of atom. The reverse process, i.e. knocking out a free electron out of the atom by a photon, began to lag behind the recombination as the universe cooled, the emitted photons lose part of its energy, so its value became not sufficient to destroy atoms. However, to one photon emitted during the recombination, there were fallen dozens of billions of others, among which there were quite energetic ones, which restrained the growth of the number of atoms. During the time interval between the moment when the number of free protons became less than that of atoms, and when the protons have practically disappeared, the temperature dropped about 100 degrees. Since then, the universe has expanded 1,400 times.