The subject of cosmology is the universe in its entirety and history. For historical reasons, it was variable because people have different understanding of the universe through the centuries. Knowledge of modern physical cosmology have accumulated from the twenties of the 20th century. Until then, it was believed that the universe was static and eternal, and there were no technical means to exceed the limits of our galaxy and other galaxies were just nebulae.
Unlike other studies in natural science, cosmology can not verify their hypotheses with experiments, but relies on knowledge accumulated from observational astronomy and of modern astrophysics
Moreover, cosmology plays a special role in the study of models such as string theory and other models of physics. For example, in string theory cosmology shows the evolution of the universe and the laws of physics by passing and adjusting them to various forms of Calabi-Yau in various stages of phase transitions of the universe.
The Big Bang Theory
The term Big Bang (English Big Bang) was introduced in 1949 by Fred Hoyle in radio program on BBC. Hoyle does not support the theory, and it tries to laugh.
One consequence of the Big Bang is that the conditions in today’s universe are different from those in the past or in the future. Under this model, George Gamow states in 1948 that the early hot phase of the universe should have left a residual radiation, which should have a range of blackbody and comes from all directions in the sky. The so-called relict radiation was discovered in the 60s of the XX century by Penzias and Wilson and serves as a confirmation of the Big Bang theory against its main alternative theory of sustainable condition.
According to the Big Bang 13.7 billion years ago the universe was infinitely dense state with huge temperatures and pressures. For the first 10-33 seconds of the universe no satisfactory physical model. General relativity provides a gravitational singularity where the density becomes infinite. To resolve this paradox is needed theory of quantum gravity. The understanding of this period in the history of the universe is one of the most important unsolved problems of physics.
In 1927 the Belgian Jesuit Georges Lemaître first hypothesis suggests that at the beginning of the universe stands “explosion” of a “primeval atom”. Before that, in 1918, the Strasbourg astronomer Carl Wilhelm Wurtz systematically measured redshift of some nebulae and called K-correction. He is not aware of the cosmological implications, nor that these nebulae were actually galaxies outside our own Milky Way.
Created at that time general theory of relativity, Albert Einstein prevents static solution – the universe must either be expanding or contracting. Einstein believed that due to wrong and tries to avoid it by adding a cosmological constant. Einstein, who was aware of the biblical idea of the beginning of time, does not accept the theory of Lemaître for “primeval atom”, as seen in her experience Lemaître to push the idea of Creation. During the general theory of relativity is applied to cosmology for the first time by the Russian scientist Alexander Friedmann whose equations describe the universe Friedmann-Lemaitre-Robertson-Walker – universe without cosmological constant.
In 1929, Edwin Hubble describes observations confirm the theory of Lemaître without being aware of it (article Lemaître was translated into English by Arthur Eddington until 1931). Established back in 1913 that most spiral nebulae identified later as galaxies away from Earth, it combines this fact with measurements of the distance determined by observing Cepheids in distant galaxies to determine that the galaxies are moving apart in all directions at speeds Earth proportional to the distance between them. Today, this phenomenon is known as Hubble’s Law.
From the cosmological principle gives two explanations of the diverging galaxies. According to one, maintained and developed by George Gamow, the universe arises from the extremely hot and dense state in the final time in the past and has since expanded. Alternatively, the theory of sustainable state of Fred Hoyle, whereby in the spacing of galaxies appears new material. In this model, the universe is roughly the same at any point of time. For a time, support for these two theories is even contact.
In recent years, observations support the notion that the universe emerged from a hot dense state. After the discovery of relict radiation in 1965. It is considered the best theory for the origin and evolution of the cosmos. By the end of the 60s many cosmologists believe that infinitely dense singularity in the cosmological model of Friedman is a mathematical idealization and that the universe is shrinking before reaching it