In 1929, Edwin Hubble found that all the Galaxies are moving away[or spreading]. Today we can say that the universe came into existence 13.7 billion years ago. Today the universe is spreading which does mean that its all compounds must be united at a point anywhere in the past which later got expand into a much larger area. The effort of the BIG BANG theory is to explain what happened in the very beginning of the universe.
According to the standard theory the universe came in the existence from as ‘SINGULARITY’ AROUND 13.8 billion years ago. Now you must be thinking what this singularity is? Actually, we don’t know it pretty surely. Singularity is the zones which refuse to obey our current understanding of physics. They are thought to exist at the core of "black holes”. A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—including particles and electromagnetic radiation such as light—can escape from inside it.
Our universe has begun as a very infinitely small hot, dense, something- Singularity. After its initial appearance, it got inflated [Big Bang], got expanded. It grew from very, very, very small and hot to the size and temperate of the current universe. After billionth of second of the big bang, it was so hot and small that it cannot be imagined by us. In this, all the 4 basic forces were present at that time, Gravitational force, Electromagnetism, Strong Nuclear force and Weak nuclear force. The all together were making SUPER forces. After the universe grew 1 second, all the basic forces got scattered. With time the universe grew older it started getting cooler.
The most common misconception with the big bang is that people think that it was a giant explosion. Rather than popping the balloon, think it as the balloon started getting inflated. Imagine balloon as singularity and inflated balloon as today's universe.
Evidence for The Theory
Firstly, it’s obvious that the universe had a beginning.
Secondly, the galaxies are moving away [according to Hubble's law]. This observation supports the expansion of universe and that the universe was compact once.
Finally, the abundance of the "light elements" Hydrogen and Helium found in the observable universe are thought to support the Big Bang model of origins.
Drawbacks of the theory We don’t know
How Big Bang happened?
How did the universe expand?
What was there before the Big Bang
Extra Point: Stephen Hawking said how the universe came into existence with Big Bang, it will come to an end with Big crunch
Written by: Aaryan Salgania
Aaryan Salgania is a Student from India volunteering for Voyager Space Outreach to write Blog Posts on STEM/Space Topics.