Big Bang Theory

The Big Bang Theory: Origin of the Universe

We all know that universe is everything. From the tiniest particles to the large stars and planets even the Sun all comes under the universe. Even the existence of space, time, and life all comes inside the universe. You must have heard about the word universe and even know about what it is. But do you know how it came into existence? There are many theories regarding the formation of the universe, ancient myths like God created the universe. However, the most accepted one is the Big Bang Theory. To be precise it is the best theory that explains the formation of the universe scientifically.

Let us proceed by knowing the meaning of the big bang theory.

Big Bang Theory

What is The Big Bang Theory?

By the name itself, you can get an idea that is only a theory and not a proven statement. Big Bang Theory is the cosmological model of the universe that we can observe. This theory explains how the universe extended from a very small particle that was full of energy.


The above picture dramatically portraits hr explosion of the Big bang. This theory explains a very broad range which includes the abundance of light elements, the CMB large scale structure, and Hubble’s law.

Now that we know that what is the Big Bang Theory let us proceed to the topic of how it is marked for the Origins of the universe.

Origin of universe – Explanation of Big Bang Theory

Ok, so let me tell you, this story of the origin of the universe is 13.7 billion years ago. Because of this time gap scientists are not able to find the accurate reason for the origin of the Universe this is why the Big Bang Theory came into the picture.

Timeline of the metric expansion of space of Big Bang theory
Timeline of the metric expansion of space

Developed into space with a hypothetical non-observable portion of the universe. In the picture, a portion of the universe formation is represented as circular sections. The left circular motion represents the inflationary epoch and the center represents the expansion acceleration.

This word big bang was given by an English astronomer Fred Hoyle in 1949 during a BBC Radio broadcast. He said, “According to this theory universe is said to be formed from a big bang or explosion of a small particle.” Although it was first suggested by a Belgian priest back in the 1920s at that time no one believed him.

This Big Bang Theory states that the universe began firstly as a hot and infinitely dense point. This was only a few millimeters wide and kind of similar to a supercharged black hole. It is stated about 13.7 billion years ago this small dot exploded violently.

Big Bang explosion
Big Bang explosion

The above GIF dramatically represents the Big Bang explosion. This explosion leads to the formation of matter, energy, space, and time. After these two major stages of evolution of the universe were formed. The first stage was called the radiation era and the latter was called the matter era.

These eras contain small key events that help to shape the universe. Firstly the radiation era came into existence. Let’s start by knowing each era separately.

Radiation era

Radiation Era symbol of Big Bang theory

The above picture is the symbol of the radiation Era. Even though big bang is just a hypothesis but the events are represented using symbols.

This Era was observed right after the Big Bang explosion. This Era was known for its radiation dominance. Radiation Era was made up of small stages called epochs which occurred during the first ten thousand years of the formation of the universe. Let’s now look into these epochs one by one.

Plank Epoch

Plank Epoch of Big Bang theory
Plank Epoch

In the radiation Era, the first epoch was the plank epoch. At this point in the universe, no matter existed. Only the four primitive or super forces, viz, gravity, strong nuclear forces, weak nuclear forces, and electromagnetic forces existed. By combining the three forces existed as one.

But at the end of this epoch, a key event took place because of which the gravity split away from the super forces.

Grand unification Epoch

After this, the second epoch started, named grand unification. If you are wondering why this name was given to it then let me tell you it was because of the unification between the remaining three super forces. The remaining super forces were Strong nuclear force, weak nuclear force, and electromagnetic force.

Grand Magnification epoch of Big Bang theory
Grand Magnification epoch

During this epoch, the strong nuclear forces from the group of three super forces broke away. This is represented in the picture above. After this epoch, three components of the super forces formed. The three parts were gravity, nuclear forces, and electroweak forces which consist of two parts:- weak nuclear forces and electromagnetic forces.

Inflationary Epoch

Inflationary Epoch of Big Bang theory
Inflationary Epoch

Then the third Epoch, called inflationary epoch begins. As you can guess by the name, this Epoch is associated with expanding the universe.

During this effect, the size of the universe changed from a small collection of atoms to a size say a big orange. The universe at this time was so hot that particles like positive and negative quarks were isolated. They were not able to come together and form particles.

Electroweak Epoch

Electroweak Epoch of Big Bang theory
Electroweak Epoch

After this, the electroweak Epoch came into the picture. During this, the last super forces, weak forces, and electromagnetic forces finally split off.

Quark Epoch

During the next epoch called the quark epoch, different varieties of atoms were present in the universe.

Quark Epoch of Big Bang theory
Quark Epoch

But the temperature of the universe was too high that it was difficult for the formation of subatomic particles. You can visualize it by seeing the picture shown above. This will give you an idea of the temperature at that time.

Hadron Epoch

After this, the Hadron Epoch came. During this Epoch the temperature of the universe cools down to combine quarks and form electro neutrons and protons.

Hadron Epoch of Big Bang theory
Hadron Epoch

This lead to the formation of numerous neutrons, protons, and electrons in the universe. These tiny particles scatter all around them space but were unable to combine because of environmental parameters.

Lepton and Nuclear Epochs

After this, the last two epochs of the radiation era came into the picture. These were the lepton and nuclear epochs. During this, the nucleons, and protons went under significant change.

Lepton and Nuclear Epochs
Lepton and Nuclear Epochs

This change leads to a combination of neutrons and protons into the nuclei. During the fusion process, the neutron and proton combined. This produced the first element which is helium. After there, the radiation era ended.

Matter era

Matter Era

This new ability of the universe to form elements out of neutron, proton and electron resulted in the matter era. The matter era was dominated by the formation of matter across the universe.

This era consists of three epochs which made the vast universe and even include the present day. Now let’s take a look at the different epochs of the matter era.

Atomic epoch

Atomic Epoch
Atomic Epoch

This was the first epoch of the matter era. During this epoch, the universe temperature cools down enough for the electrons to attach to the nucleus and hence formed another atom called hydrogen. The process by which the electron attached to the nucleus is called recombination.

Galactic Epoch

Galactic Epoch
Galactic Epoch

Now the next epoch called the galactic epoch started. During this, the hydrogen atoms along with Helium atom formed clouds all over the universe. Inside the clouds, gas had enough gravity to combine two atoms. These became the pillars of the Universe which we are seeing today.

Stellar Epoch

The next and the epoch which we are in today is the stellar epoch. During this epoch, inside the helium and hydrogen clouds, stars started to form and it caused a huge repeal effect.

Stellar Epoch
Stellar Epoch

The heat between the starts leads to the conversion of hydrogen and helium and formed almost all the elements in the Universe. These elements ultimately became building blocks for the formation of planets, sun, and every other heavenly body that is present today. These became the key to life on our planet.

All this event leads to the formation of each and everything in the universe which we can see or which are present but we cannot reach them.

Why the Big Bang Theory is the most accepted theory for explaining the formation of the universe?

We all know that there are many theories regarding the formation of the Universe. But why Big Bang is the most accepted one? To know this we must know the special features of this model. The features are the reason for its wide acceptance.

Two main parameters for acceptance of Big Bang

One of the main reasons for the acceptance of this theory is it explains many phenomena like light elements, the CMB, large scale structure, and Hubble’s law.

This theory of Universe formation depends on two parameters. The first one is the universality of physical law which is one of the underlying principles of the theory of relativity. The other parameter is the cosmological principles. According to the cosmological principle, the universe is isotropic and homogeneous.

These parameters or ideas were initially taken as just theories but later some tests were run to prove them or make them possible in real life. For instance, the universality of physical law was tested on the fine structure constant. After this experiment, we knew that the age of the universe is of order 10-5. Apart from this, the general relativity has also tested on the scale of the solar system and binary stars.

The reason is the expansion of the Universe!!

Other than these two parameters, big bang also contributed to the theory of the expansion of the Universe. This was one of the reasons for the acceptance of the Big Bang.

Expansion of Universe
Expansion of Universe

The main feature of the theory was the presence of particle horizons. This was made on the assumption that our universe is somehow finite and so the light travels at a finite speed. Due to this, there may be some objects whose light hasn’t reached us yet.

FLRW model
FLRW model

These places have a limit or past horizon of the most distant objects we observe. On the other hand of the universe is expanding then it may happen that some objects light will never reach us. This is because the light has h specific or finite speed. So if the objects keep on moving away, it is sure that those objects light cannot reach us. The name of this process is the future horizon. The presence of both the future and past horizon depends on the FLRW model of the universe.

There are concepts of the existence of both the horizons. The knowledge of the universe of early times suggests the existence of the past horizon. But, if the expansion of the universe constantly gets accelerated then there is a scope of future horizon too!!

Observable evidence of Big bang

We all know that science needs evidence, not theories.

Even though the Big Bang is just a theory, some considerable evidence related to it has been observed. Let us look at that evidence which has been found till now.

Hubble’s law and expansion of space

The earliest observation for the existence of Big Bang theory was the expansion of the Universe which was stated by Hubble’s law.

This law says that the distant observed galaxies and planetary bodies are red-shifted. In simple words, we can say that they are expanding. Yes, according to this law the galaxies and other heavenly bodies are moving at a speed which is proportional to their distance from Earth. In other words, we can say that the farther they are the speed increases.

Here goes the expression for Hubble’s Law:- ѵ = HoD

  • ѵ is the recessional velocity of the galaxy or any other heavenly bodies.
  • D is the distance of Earth to the objects.
  • Ho is the Hubble’s constant whose value is around 70.4+1.3
resistance velocity versus distance graph for Hubble's law
resistance velocity versus distance graph for Hubble’s law

In the above picture, you can see a graphical representation of Hubble’s relationship or the law. The graph shows that with the distance the velocity of expansion increases.

Hubble’s law that has two possible explanations. It says that either we are at the center of the galaxy which was unexplained under the assumption of the Copernican principle. the other one is that universe is expanding uniformly from every other direction.

The expansion of the universe was first predicted by Friedmann in 1922 and by Lemaìtre in 1927 which was based on the general relativity. After this Hubble analyzed in 1922 and observed regarding the expansion of the universe. These all became the concrete proof of the Big Bang theory.

Cosmic microwave background radiation

The discovery of cosmic microwave background radiation was a kind of accident. In 1964 Arno Penzias and Robert Wilson discovered the existence of CBR( Cosmic Background Radiation)which was and single directional microwave band.

CMB radiation
CMB radiation

This discovery of CBR proves to be the most concrete evidence for the existence of the Big Bang.

The Big Bang theory predicted that when the explosion happened the heat transmitted from the explosion got distributed among the space. The evidence for this theory existed. When this assumption was made a temperature value was given and the network assumes that the temperature of the Universe dropped 2.7°. The scientist said that the temperature should have cooled down around 2.7 degrees above the absolute 0° and the practical value was the same as theoretical.

When the cosmic background radiations were found the temperature was the same as theoretical. This came out to be a huge turning point for Big Bang.

Different elements present in space

We know that every star every planet which is present in the universe does not have the same composition. This means that every other heavenly body does not have the same amount of elements present in them. Maybe some bodies have a single kind of element which is not present in any other.

According to the Big Bang Theory, during the explosion and cooling down process some elements were created which further went under changes and created a variety of elements. This means that the process is continuing and new elements are being created. The existence of different elements and different composition of every heavenly body indicates that the big bang is correct.

This is true because for example the elements which are present in the Sun and not present in the stars which are younger than the sun. Because the sun was made 7 billion years ago and some start which are 3 billion years old does not contain the same elements.

Drawbacks of Big Bang Theory

Some scientists constructed the existence of the Big Bang Theory. Here are some of the points which they highlighted.

  • The first conflict was regarding the violation of the law of Entropy. This was due to the explanation of the formation of stars and Galaxy Through The Big Bang. cording to the law of Entropy system of change become less organized over time. But if we view the early universe it conflicts the law that the universe today.
  • Some scientists say that the evidence regarding the existence of redshift or cosmic background radiation are misconceptions. They also said, there is some kind of cosmic body whose formation can be explained by Big Bang Theory but they did not exist in reality.
  • The early period of The Big Bang Theory also highlights the rule that nothing can travel faster than light. This is because according to theory space can expand faster than light.

Myths regarding The Big Bang Theory( TV series)

So, now that we know almost everything about the big bang, there is one myth regarding a TV series which goes by the same name!!

Yes, there is an American TV series ‘ The big bang theory’. This was telecasted from 25th September 2007 to 16, May 2019. It is a sitcom drama, about 5 friends who lived together in an apartment.

By seeing the name you might have to get confused that this television show is somehow related to the big bang explosion or somehow it has explained the facts or it is some kind of sci-fi television show. You might have decided to watch it for learning more about the big bang.

But let me tell you, it is not at all related to the Big Bang of the universe. It is just a story of 5 people out of which 3 worked in the science field. This can be the reason for which this name was given to the series.


We know that the big bang is just a theory, but there are some proves for its existence or which points out that it happened. But some points are so their which contradicts the big bang.

But understanding this theory is also very important as this somehow suggests the framework and building of the universe we live in. There is also a future scope that this theory can even explain the ending of this Universe. With the advancing technology, we can explore the space and ability to find real evidence that indicates towards big bang. However, till now it is just a theory and proper proofs are still to be found.

Frequently asked questions

Who discovered the big bang theory?

This theory was first proposed by a Belgian priest named Georges Lemaître in the 1920s.

What was third before the big bang?

There are not any certain answers to this. Some believe that, before the big bang, there was one fundamental force which was located nowhere.

Is the American TV series ‘The Big Bang Theory’ is related to the big bang explosion?

The American TV series is not at all related to the big bang. It is just a story of 5 friends who shared an apartment.

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