The radius of the Universe was equal to zero 10-13 billion years ago, at the primordial moment in time. The density of energy is infinite, so is the density of substance. Total energy of the Universe and its total mass were concentrated in zero volume. Such a state is known as singular state.
In 1946 George Gamov and his colleagues developed a physical theory of the initial stage of expansion of the Universe. The theory explained the creation of chemical elements as a result of synthesis at highest temperatures and pressure, and a consequent "explosion" of energy and matter. This is why Gamov's theory is known as the Big Bang theory.
According to theoretical calculations, energy per unit of volume remained constant and the Universe expanded with a velocity that was much higher than the velocity of light during first 10-36 s, when the temperature of the Universe exceeded 1028 K. This fact does not contradict the principles of relativity since space, and not only substance, expanded with such velocity. This stage of evolution is known as the inflation stage. Modern quantum physics holds that strong nuclear interaction became independent from the weaker electromagnetic forces at that time. This loss of symmetry spurred an incredible emission of energy, which accounted for the dramatic expansion of the Universe. The Universe grew from the size of an atom to the size of the entire Solar System in the period of 10-33 seconds. The elementary particles, as well as a slightly smaller number of antiparticles appeared at the same time as a result of spontaneous disturbance in force symmetry.
Substance and radiation still maintained their thermodynamic balance, and "hot" photons completely determined the radiation pattern of Universe. This epoch is known as the radiation stage of evolution.
Recombination stage occurred at the temperature of 5∙1012 K. Almost all protons and neutrons that have been annihilated in the previous stages became protons again. Only those particles that lacked antiparticles were left. Observations prove that nearly one billion protons accounted for creation of one baryon. It follows that the initial relationship of particles as compared to antiparticles was equal to one billion to one. The matter of observed Universe mainly consists of this "excess" substance.
The stage of initial nuclear synthesis, when nuclei of heavy hydrogen and helium were formed, started a few seconds after the Big Bang. It lasted for around three minutes, and was followed by calm expansion and cooling-down of Universe.
The balance between substance and radiation was disturbed approximately one million years after the Big Bang. Atoms started forming from free protons and electrons. Radiation began to pass through substance as it would through a transparent medium. This radiation came to be known as relict radiation. Its temperature was around 3 000 K. Wavelength of relict photons increased as the Universe expanded. At centimeter bandwidth, the temperature of background radiation is presently 3.5 K. U.S. scientists Arneau Penzias and Robert Wilson discovered relict background radiation in 1964. Relict radiation is highly isotropic, and consistent in magnitude in all directions. It serves as a confirmation of the model of a hot, expanding Universe by its very existence.
Protogalaxies emerged as a result of density variations in substance that emerged during the inflation stage in accordance with Heisenberg's principle of uncertainty. Sources of gravity formed in those areas where the density of substance was slightly above average as compared to the general composition of the early Universe. Regions with reduced density became progressively more rarefied since substance gradually migrated towards the denser regions. Thus, a virtually homogenous medium was eventually split into separate galaxies and clusters.
First stars appeared hundreds of millions of years later.
The question pertaining to the origin of Big Bang, i.e., what existed prior to its occurrence, is still open to deliberation. Was there a universe just like ours? Was there an absolutely different world, guided by different natural laws? These questions remain to be answered in the XXI century.
This model enables you to track the evolution of the Universe since the moment of the Big Bang to our time. Slides in the central window display the landmark stages of evolution. Use the scale at the bottom part of the model to switch the slides.
You may also watch the slides in a continuous mode. Press "Run" button. Slides will alternate at a 3 second interval in a predetermined sequence, starting with the current one. "Stop" button suspends the animation. Press "Reset" button to return the model to the slide.