What is the 'Big bang' theory regarding the origin of the universe ? Explain the various evidences favouring this theory.

What is the 'Big bang' theory regarding the origin of the universe ? Explain the various evidences favouring this theory.   10
Ans: According to the big bang theory, the universe began by expanding from an infinitesimal volume with extremely high density and temperature. The universe was initially significantly smaller than even a pore on your skin. With the big bang, the fabric of space itself began expanding like the surface of an inflating balloon – matter simply rode along the stretching space like dust on the balloon's surface. The big bang is not like an explosion of matter in otherwise empty space; rather, space itself began with the big bang and carried matter with it as it expanded. Physicists think that even time began with the big bang. Today, just about every scientist believes in the big bang model. The evidence is overwhelming enough that in 1951, the Catholic Church officially pronounced the big bang model to be in accordance with the Bible.
Evidence for the Big Bang theory:
1. Redshift of Galaxies: The redshift of distant galaxies means that the Universe is probably expanding. If we then go back far enough in time, everything must have been squashed together into a tiny dot. The rapid eruption from this tiny dot was the Big Bang.
2. Microwave Background: Very early in its history, the whole Universe was very hot. As it expanded, this heat left behind a "glow" that fills the entire Universe. The Big Bang theory not only predicts that this glow should exist, but that it should be visible as microwaves - part of the Electromagnetic Spectrum. This is the Cosmic Microwave Background which has been accurately measured by orbiting detectors, and is very good evidence that the Big Bang theory is correct.
3. Mixture of Elements: As the Universe expanded and cooled down, some of the elements that we see today were created. The Big Bang theory predicts how much of each element should have been made in the early universe, and what we see in very distant galaxies and old stars is just right.
4. Looking back in time: The main alternative to the Big Bang theory of the Universe is called the Steady State theory. In this theory, the Universe does not change very much with time. Remember that because light takes a long time to travel across the Universe, when we look at very distant galaxies, we are also looking back in time.