A Belgian priest named George Lemaitre firstly suggested the idea of big bang theory in age 1920s.
The actual beginning of everything may not be explain by Big Bang Theory.

13.8 billion years ago, an explosion occurs because of every speck of energy dense into a very tiny point called singularity. This explosion was beyond the imagination.
After this explosion, all the matter spread in all over surrounding directions with very high speed approximate speed of light. The temperature at that time was 1000 trillion degree Celsius.

Events after big bang-

After Big Bang, in initial three lakh years, all the matter was in plasma state. After this, the protons and neutrons combine together and form nuclei and then a complete atom.

The first atom formed after Big Bang was Hydrogen atom and then Helium by hydrogen’s fusion, then higher atoms.

The atoms combine and form small terrestrial bodies then stars, planets, galaxies and our universe.

The estimated numbers of atoms in the present universe are approximately 10⁷⁸ – 10⁸².

Expansion of universe

The expansion of universe is the main evidence for the existance of big bang. According to some theories, the universe is still expanding after big bang. It is predicted by the light coming from other galaxies that the galaxies are moving far away from our galaxy (milky way).

According to planck’s observations the rate of expansion of universe is 67km/sec/megaparsec. But according to present understandings of universe it is 9% faster rate then planck’s prediction.

During big bang, the infrared light form. But now we observe these rays as cosmic microwaves.

According to some theories there are other universe like our universe called multiverse.

Our universe form after big bang and expanding, but after some billion years it would be contracted and again a big bang occurs. This cycle would be happen continually, called oscillating universe.

If we see the stars in space, it means we see the past of stars because light can take thousand years reach to earth from these stars.

Experiment related to big bang

Physicists create conditions of big bang by a gigantic machine called Large Hadron Collider (LHC). The LHC is an 27km long underground tunnel in ring shape.

It comprises superconducting magnets to accelerate the particle (protons and heavy ions) inside the tunnel.

In LHC, two particles accelerated close to the speed of light. The accelerated particles collide and produce extreme energy. By these conditions, physicists understand that how big bang creates the universe.