Inflation ( 10^{– 43} s )

Modern science is unable to answer the question about the Universe origin. There are many guesses on this subject. Many of these agree on the inflation (a superfast Universe expansion) period followed by the Big Bang. Initially, the Universe size was extremely small, ~10^-33 cm, but it increased up to almost 1 cm within a short period of 10^-36 seconds! The inflation theory managed to explain a lot of questions, which nonplussed physicists for a long time. The end of inflation period was accompanied by the Universe quick warming up – a release of huge amount of heat, usually referred to as a Big Bang.

Electroweak phase transition (ns)

The Universe is filled with hot (10¹⁶ – 10¹⁷ K) plasma. Weak and electromagnetic interactions, being united before this period, become independent by now. Electromagnetic force is carried by massless photons. W^± and Z⁰ bosons carry weak force and acquire mass because of their interaction with Higgs field, which makes weak interaction a short-range one. It acts at the distances by a factor of thousand smaller than a nucleus size. Interactions between charged bodies and particles, as well as elastic, viscous, molecular and chemical ones relate to the electromagnetic interaction. Weak interaction is responsible for stars energy release and nuclei radioactive decays at the micro level. Besides the electromagnetic and weak interactions, there is also a strong interaction, which accounts for the bind between protons and neutrons in nuclei, and for gravitational interaction, providing attraction of all non-massless bodies.

Quark-hadron phase transition (1 μs)

A so called “quark soup” existed in the early Universe at temperatures higher than 10¹¹ K. According to modern concepts, quarks are elementary particles with fractional charge. Protons and neutrons consist of quarks. As a result of Universe expansion, temperature decreases, and quarks start to bind, forming protons and neutrons. Quarks, protons and neutrons are called hadrons. It means these particles participate in the strong interaction.

Nucleosynthesis (3 min)

Nucleosynthesis is one of the most important stages of the Universe evolution. Space expansion and, consequently, Universe cooling result in the fact that it becomes favorable for protons and neutrons to combine into nuclei. Light nuclei (up to carbon nuclei) are formed because of thermonuclear reactions. Carbon nuclei will be formed much later as a result of thermonuclear reactions in stars. Along with protons, helium nuclei appear in the Universe, too. When the nuclei formation processes take place, Universe approximate lifetime is about hundred seconds. Typical temperature values for this Universe evolution stage are 10⁸ – 10¹⁰ K.

Recombination (400000 years)

About 200 thousand years after the Big Bang, the Universe temperature decreases down to approximately 3000 – 4500 K. Formerly free electrons combine with light atomic nuclei and protons. Atoms of hydrogen, helium and of other light elements are formed during the recombination. As a result, the Universe becomes transparent for photons – relic radiation, which is registered with detectors nowadays.

Galaxies formation (1 billion years)

Galaxies start to form after a billion years after the Big Bang. We see these galaxies in the night sky nowadays. According to one of many theories, their formation prerequisites were laid at the inflation expansion stage, when density perturbations were formed from scalar field quantum fluctuations. These  fluctuations, usually showing up in microscopic scale only, quickly increased in the exponentially expanding Universe.

Nowadays (13.7 billion years)

We observe our modern Universe after almost 14 billion years after the Big Bang. The Universe contains 10¹¹ galaxies, its size is about 10²³ km. Our planet revolves around a star (Sun), one of hundreds of billions of the Milky Way galaxy stars. According to the latest ideas, the formation of our Solar System started about 4.6 billion years ago with a gravitational collapse of a small part of giant interstellar molecular cloud. The Earth formed about 4.54 billion years ago due to an accretion from the solar nebula. Human existence period is negligible compared to the Universe age; however, we already managed to recreate temperatures and energies of the world first instants in our scientific laboratories. Thanks to modern technologies, amazing possibilities for research open up before scientists’ eyes.