The term Big bang was coined by the British astronomer Fred Hoyle who was actually a opponent of this theory. He developed an alternative The Steady state theory. According to this steady state theory the universe remains stable since the decreasing density caused by expansion is balance by the constant creation of new matter.
In 1929 after spending many nights in taking photographs of the universe with the latest telescopes he concluded a fascination discovery otherwise called Red Shift theory. According to this the galaxies appear to be moving away from our own and they are receding at faster speed the farther away they are. The spiral arms of the various galaxies are expanding this concludes that at some point of time the universe was a small un imaginable dense mass of matter.
In 1946 astrophysicist George Gamow suggested that if the big bang theory is correct, the receding energy would have to leave the traces in the form of cosmic noise or backward radiation. The existence of this radiation was conforming in 1965 by two American radio astronomers. They detected a background radiation present in all parts of the heaven.
Years later the uniformity of temperature becoming puzzling for the supporters of the big bang theory the background radiation indicates the matter was distributed uniformly in the space. But the matter is concentrated into galaxies this raised the question of the origin of Spiral galaxies.
The Big bang theory rest pm the quantity of helium present in the universe most of the chemicals are born from the stars. However helium accounts for 23% of all matters of universe, it is impossible that all originated from the stars. Therefore we have to assume that they were existed before the formation of stars.
There are so many unsolved mystery and doubts in the big bang theory:
1) It is not possible to study the first moments of Cosmos- The very beginning of time and space.
2) Many scientists regard the existence of quasars as another obstacle to the big bang
theory. Quasars are the cores of active galaxy and hence some scientists believe that their properties are in conflict to the big bang theory.
The observation made so far revealed the universe is still young but the astrophysical theories based on the assumption that they were 13 thousand million years old.