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What is Big Bang Theory?

Updated on 29 December 2020
Bsc Courses
7 min read 8 views
Updated on 29 December 2020

There have been many theories and speculations on how our universe was created. This seemingly infinite place inside which we live now has always been a puzzle and mystery to humans. How it originated and what would be its possible end, are some of the fundamental questions which are being asked continuously since men have begun to think. Common men, scholars, philosophers, scientists all have given their theories.

But today many scientists agree on one particular theory for the origin of the universe, and this theory is famously known as the “Big Bang Theory”. So, what happened during the big bang? Some of the leading scientists, astronomers and cosmologists believe that our Universe was created after a massive explosion. All the matter which is part of our Universe and all the laws by which it is governed are the results of this single most phenomenon.

It must be kept in mind that the big bang theory is not the only theory that tries to explain the origins of the universe, there are some competing modern theories such as the Steady State Theory (a.k.a. Oscillating Universe Theory) which also explains the phenomenon well. However, Big Bang Theory is now the most widely accepted and popular.

The reason for acceptance may be attributed to the explanation of the origin of all known matter, the laws of physics, and the large scale structure of the Universe. It also explains the phenomenon of a “continuously expanding universe”.

Now the question arises what is the Big Bang Theory all about, which we shall try to explain under the next few headings.

What is the Big Bang Theory?

The simplest explanation of the Big Bang is that it is the phenomenon through which our universe began. 

It is the idea that the universe began from one single point. This single point began to stretch and expand due to an explosion inside. This explosion and expansion have created all the matter and laws within our universe. From that single point to the present time, the universe is still expanding and will continue to do so till eternity. All of this occurred around 13.8 billion years ago.

The Big Bang theory has prominently born out of the observation that the galaxies around us are moving away from our own galaxy in all directions. This is the most simplified and known explanation for how did the big bang happen from nothing.

Who discovered the Big Bang Theory?

The fundamental tenets of the Big Bang Theory were given by an astronomer Georges Lemaitre in the year 1927, however, this story has been continuously developed by other scientists and astronomers. 

The Belgian astronomer and priest Georges Lemaitre suggested the prominent ideas of Big Bang in 1927. He proposed that the universe began from one single primordial atom. He also gave the fundamental assumption of the theory that the universe is stretching and expanding from that point onwards. 

Lemaitre’s theory got a major nod when Edward Hubble asserted upon his astronomical observations, that the galaxies are going far away from us in all directions. 

Additionally, the discovery of the Cosmic Microwave Radiation by Arno Penzias and Robert Wilson added credibility to Lemaitre’s Theory. 

The term “Big Bang” however was coined by another astronomer Fred Hoyle, in the year 1949.

So what existed Before the Big Bang?

The best explanation of everything before the Big Bang is that the universe was an infinite stretch of dense material that was extremely hot. This material was “steady” and remained in this state until the Big Bang occurred. 

This steady, dense and ultrahot universe that existed before the Big Bang may have been governed by the laws similar to Quantum Mechanics (which is the physics of extremely small scale).


Stephen Hawking viewed this state before the Big bang as something immeasurable and undefined. Hawking termed his explanation, the No-boundary Proposal (in 1983). According to this “proposal”, time and space have no starting or ending points. Time and space are finite as well. 

Hawking had a very interesting explanation of what existed before the Big Bang

In an interview, he said that in order to understand the pre-Big Bang time, you need to take your universal remote, and press the rewind button. 

Now rewind enough to the time of the Big Bang (i.e. 13.8 billion years ago). At this point in time, the universe had shrunk to the size of a single atom. 

This subatomic ball of an atom can be termed as Singularity. This Singularity is extremely infinitely small and is a densely packed material of heat and energy, Inside this infinitesimally small subatomic ball, the laws of physics and time cease to exist. 

In other words, Time didn’t exist before the Big Bang.

(Because as the direction of time shrinks infinitely, thus it never reached a clear starting point).

Hawking said that the time was bent and "it was always reaching closer to nothing but didn't become nothing".

And What happened During the Big Bang?

At the point when the universe began to form, it was just a hot, tiny subatomic ball of light and energy( as explained by Hawking). And out of nowhere, an explosion occurred. This was around 13.8 billion, a very long time, we guess.

In the immediate seconds followed by the Big Bang, the surrounding temperature was about 5.5 billion degrees Celsius. At this moment, the cosmos got filled with fundamental particles such as Electrons, Neutrons, and Protons. Gradually, these particles combined as the universe began to get cooler.

This mixture of particles could not be distinguished as there was darkness due to the absence of any form of light. According to NASA, the light which came afterwards may have been caused by the free electrons.

This early light is termed as “afterglow”, scientifically it is known as the Cosmic Microwave Background (CMB). The discovery of CMB added a new level of acceptance to the Big Bang Theory in the 1960s. This is the most simplified and accepted theory for the question What happened during the big bang?

The Big Bang Timeline

As stated earlier, what we now know as the Universe began to originate nearly around 13.8 billion years ago. Atoms, molecules, light, energy, stars, galaxies, asteroids, comets, planets and black holes, all have formed after the cosmic explosion of the Big Bang. 

The following picture shows the timeline of the Big Bang and the expansion of space.

Image Credits- Earthsky.org


The Big Bang Theory didn’t come easily. The scientists have painstakingly pieced together the history of our universe back to 0.0000000000000000000001 seconds (10 -21 seconds) after the Big Bang. Tracing that how the Big Bang happened from nothing has been very challenging. This reconstruction of ~14 billion years old history is based on the threads of existence visible to us today and is only possible through a half-century of laborious observations. 

The Big Bang Theory undoubtedly is one of the crowning achievements of our species. Other theories definitely may come in the future, however, this one makes the most sense in the history of mankind. 

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