Birth of Universe-The Big-Bang

Let us start with our first (and most probable) hypothesis-Big Bang. Actually Georges Lemaitre proposed this theory. This theory is mainly based on three laws, namely: -
1) General relativity
2) Homogeneity
3) Isotropy

According to Big Bang theory, the universe is expanding or we can also say that the galaxies are moving away from each other. Law of Doppler shift proves this. So, if the universe is continuously expanding it suggest that the evident expansion in forward time required that the universe contracted backwards in time, and would continue to do so until it could contract no further, bringing all the mass of the universe into a single point, a "primeval atom", at a point in time before which time and space did not exist. As such, at this point, the fabric of time and space had not yet come into existence. If we try to extrapolate this view we will reach a point when it is not possible to contract the universe any more and we will get a primeval atom with super high density and energy.

We will try to understand this concept using the example of football. We will try to correlate both the cases. Consider a football, think it as the primeval atom (starting point of whole universe). Now suppose we are pumping air in this football and we go on pumping till the football explodes. This point of explosion is known as Big Bang. Now as the football explodes the fragmented parts start flying away from each other. These fragmented parts correspond to the galaxies and they go on moving away from each other.

This is the basis of Big- Bang theory. I will try to explain this theory in more detailed manner (theoretically and mathematically) in my further posts.