What is Big Bang Theory?
Big Bang Theory is one of the theories put forward to explain the origin of our universe. Of all the theories that have been put forward till date, this theory seems to explain what we see around us the best.
As it is supported by many observations, it’s no surprise that it is the most accepted theory of the origin of universe nowadays. However, there are many grey areas even now. It cannot explain everything and so it is still evolving – a work in progress.
In this article, we will study about the Big Bang theory in some detail.
Table of Contents- Origin of Universe as per Big Bang Theory
- Stages of the creation of Universe as per Big Bang Theory
- Lacunae in Big Bang Theory
Origin of Universe as per Big Bang Theory
As per the Big Bang Theory, universe originated from nothing. Initially all the mass of the universe was concentrated at a single point of singularity, which was very dense, and very hot.
Then because of some reason an explosion happened (around 13.7 billion years ago), referred to as the “Big Bang”. This created space, time, matter and energy.
NoteTo tell you the truth, there was no explosion. At the start the space just started expanding. The term “Big Bang” is a misnomer.
That is, as per this theory the universe is not infinite or ageless. It has a start and so a boundary and a certain age. Earlier, many theoretical physicists used to believe in the theory of Static Universe, as per which the universe is static - it’s not expanding and has no start or end.
Big Bang Theory challenged this theory of static universe, and now because of many observations that support it, the Big Bang Theory is the most accepted theory of the inception of our universe. Some of these observations are:
Observation by Edwin Hubble, that most of the galaxies are moving away from each other, which means that the universe is expanding.
Discovery of Cosmic Background Radiation in 1964 proved to be the most important factor in validating the Big Bang Theory. The smoke coming out of a gun indicates that the gun has recently been fired. Similarly, Cosmic Background Radiation proved that there had been a big explosion at the beginning of the universe.
Hubble telescope and other advanced tools have given us a clear idea of the extent of our universe since then, and also the rate at which it is expanding. Now we understand that not only is our universe expanding, but it’s doing so at an accelerated rate.
But what does the Big Bang Theory say exactly? Let’s dive into the details of this theory.
Stages of the creation of Universe as per Big Bang Theory
Development of universe can be divided into two main eras, each of which can be further classified into various epochs:
Radiation Era – This era came first. During this era there was dominance of radiation in the universe. It consists of the following epochs: Plank, Grand Unified, Inflationary, Electroweak, Quark, Hadron, Lepton, Nuclear.
Matter Era – It consists of the following epochs: Atomic, Galactic, Stellar.
Let’s study some of these in more detail.
Plank Epoch
It’s the earliest phase of the universe after the big bang. Temperature was around 1040 Kelvin.
No matter existed in the universe at this time. There was only energy.
Even the four fundamental forces of nature (i.e. gravity, electromagnetic force, weak nuclear force and strong nuclear force) were not existing separately. They were combined together in the form of a super force. This epoch ended when gravity came into existence.
Grand Unification Epoch
This started 10-43 seconds after the big bang. Temperature was around 1036 Kelvin.
This epoch ended when strong nuclear force came into existence.
Inflation Epoch
This started 10-35 seconds after the big bang. Temperature was around 1033 Kelvin.
In this time period, the universe expanded pretty rapidly, from the size of an atom to that of a ball. So, the temperature of the universe fell rapidly too.
Energy started manifesting into elementary particles like gluons, electrons, quarks, and anti-quarks. But as the temperature was very high, those newly formed elementary particles were not very stable. So, in this stage the energy was creating matter, and the matter was getting annihilated to form energy.
Electroweak Epoch
This started 10-32 seconds after the big bang. Temperature was around 1020 Kelvin.
Weak nuclear force and electromagnetic force came into existence. So, by now all the four fundamental forces of nature came into existence, i.e. gravity, electromagnetic force, weak nuclear force and strong nuclear force.
Quark Epoch
This started 10-12 seconds after the big bang. Temperature was around 1016 Kelvin.
All the basic ingredients of the universe were already present, all the quarks, electrons etc. Also, all the four forces of nature were existent. However, as the temperature was very high, these particles failed to combine together to form bigger particles.
Hadron and Lepton Epoch
This started 10-6 seconds after the big bang. Temperature was around 1010 Kelvin.
The universe was more than a billion kilometres in diameter, and so its temperature started dropping quickly. Quarks became stable and started forming even bigger elementary particles, e.g. protons and neutrons.
Nucleosynthesis Epoch
This started 1 second after the big bang. Temperature was around 109 Kelvin.
One second after the big bang, the universe was over 100 billion kilometres wide. And so, it was cool enough to form atoms, and the first element Hydrogen came into existence.
After the end of radiation era, which lasted for around 50 thousand years, the next era of the universe started – the Matter Era. Matter became predominant. This is the era that we are living in even now. Let’s see some of its epochs.
Atomic Epoch
This started 50 thousand years after the big bang. Temperature was around 3000 Kelvin.
Universe has cooled down enough for the electrons to get attached with the nucleus. So, the second element came into existence – Helium (H2).
Galactic Epoch
This started 200 million years after the big bang. The hydrogen gas and the helium atoms present in the universe started coming together because of gravity and form clumps of gas and matter clouds. These were the seeds of the future galaxies.
Stellar Epoch
This started 3 billion years after the big bang. The first stars came into existence due to the extreme pressure and temperature at the centre of the hydrogen clouds. So, light came into existence. This is the stage of the universe that we are living in right now.
Stars converted hydrogen and helium into higher elements, such as carbon, nitrogen, iron, gold etc. These in turn, became the building blocks of planets, satellites, organic life etc.
Lacunae in Big Bang Theory
As we mentioned earlier, there are still many things that cannot be explained by Big Bang theory. In fact, there are some dimensions of this theory that are beyond the comprehension of scientists. Let’s have a look at some of them.
What caused the Big Bang?
Though the Big Bang Theory can explain a lot of things that happened after the big bang, it fails to explain the cause of the Big Bang. This is the most critical question regarding the origin.
Was there something before the existence of our universe, or was the big bang result of some white hole that originated from a black hole in another universe, or did it happen because of the collision of two universes? This theory has no answers regarding it.
And because of it, theologists see it as a proof of the existence of some superior being. Someone who caused “Big Bang” to happen. We see this in Bible, where the God first created the universe and then decided that there be light. As per Hindu scriptures, universe originated from nothing – sounds very similar to the theme of the Big Bang Theory. However, these are mere speculations. Nothing can be said with certainty.
So, this theory can answer what happened after the big bang, but cannot answer why big bang happened.
Issue of Singularity
This is the biggest issue with the Big Bang Theory. When theoretical physicists do the maths, this theory keeps on throwing infinity at them, i.e. a point having infinite mass.
As per this theory, at the beginning all the mass of the universe was concentrated at a single point of infinite density, called the point of singularity. Then something happened and an explosion caused the universe to expand very quickly, and the elementary particles, space and time came into existence.
However, scientists cannot explain the nature of the initial point of singularity. Even in case of black holes, we encounter the same problem. That’s the reason why we cannot explain what is inside a black hole.
To find out what happened at the beginning of the universe, at the moment of the big bang, we need the theory of everything, i.e. a grand unified theory that combines the following two theories:
- Einstein’s theory of relativity – that explains the big particles and objects of the universe.
- Quantum theory – that explains the behaviour of elementary particles.
This is still a work in progress. If anyone can achieve this unification, then it probably will be the biggest discovery in physics.