Big Bang Theory; Observational Evidence

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What is the Big Bang model?

According to the Big Bang theory, the universe was once a small clusters of volume with extremely high density and temperature. The universe was initially very small. The big bang theory states that the universe was initially a tight, condense ball of matter. The big bang theory is the theory that stated that space began to expand like a surface of an inflating balloon. Unlike popular belief that the Big Bang theory was a big explosion, it was not an explosion at all in an empty space. Space itself began with the Big Bang theory and it carried matter with it as it expanded.
Most people in the 1900s assumed that the universe was fixed in size. In the 1915, there are new possibilities that opened up when Einstein formulated his famous general relativity theory that described the nature of space, time, and gravity. The theory allows for the expansion or contraction of space. In 1917, both Willem de Sitter and Alexsandr Friedmann reached the same conclusion that the universe was expanding. All matter contained in tiny universe and expanded.
There are three main observations that explained that the universe began with the big bang theory. One observation is that the universe is expanding; there is separations between galaxies that become larger and larger. This led astronomers to deduce that everything used to be extremely close together before some kind of explosion happened.
The idea of the expanding universe was verified by Vesto Slipher who noticed that there are more galaxies going away from us than approaching us. Scientist know that galaxy is approaching or receding by looking at the spectrum of its light. If spectrum is shifted toward shorther wavelength or blueshift), then the ...