The Big Bang theory is the cosmological model for the universe from the earliest known periods through its subsequent large-scale evolution.

The universe is everything, from the tiniest particles to the largest galaxies and to the very existence of space , time and life, but when did it all begin? everything started with the big bang, the idea that the universe was suddenly born and is not infinite. For a long time we humans had no idea what was going on in the universe,so to help, we made up stories to either help us explain what we saw or to make us feel better about what we didn’t understand, but then science came along and we began to understand things more closely and logically. By the turn of 20th century scientist knew that the Earth was old. Darwin’s theory strongly implied that the Earth was atleast millions of year old and Lord Kelvin confirmed that the Earth was ancient given that it cooled from an initial molten state. Therefore the universe itself must be logically as old or even older than the earth which started with a Big Bang or did the Universe start with a Big Bang? what is the big bang science? or what is the big bang theory? 

A very popular idea was that the universe was static which also was predicted by Einstein, which meant it was always existing in the same way it is now. It always had everything that we see in it today. When we observe something in astronomy we try to fit it with already existing models and theories. But when something doesn’t fit the existing framework then it is a problem. Science is a tapestry, when we yank a thread, the whole structure needs to be weaved again. In 1921 astronomer Vesto Slipher started talking spectra of the spiral nebula hoping to get some insights on their characteristics. But to his astonishment he found that in all the spectra he recorded , was red shifted which clearly indicated that the whole system was moving away from us at a very fast speed. At this point physicist Georges Lamaitre ,who was studying Einstein’s work found that his equations fitted an universe which was expanding rather than a static one. Together with Slipher’s observation he concluded that the universe was expanding. In 1964 by accident, cosmic background radiation was discovered in relic of the early universe which together with the other observational evidence confirmed the above stated fact. Therefore the Universe was not static and had been expanding with time. So if we could turn back this cosmological clock it clearly suggests us that the universe must had started from a dimensionless singular dot. Gradually the Big Bang was accepted as a theory in science. Since then improved technology like the Hubble telescope has given us pretty good picture of the big bang and structure of the Cosmos. Recent observations even seem to suggest that the expansion of the universe is accelerating, but how did this big bang work? How can something come from nothing lets explore what we know.

From the Big Bang explosion we got :



The evolution of the universe since the Big Bang can be divided into two stages:

1. Radiation Age

2. Matter Age

1.The Radiation Age

(named so because of the dominance of radiation)

This age is further made up of smaller stages called epochs.

1.1 Planck Epoch

Temp : 1040 Kelvin

Time after big bang: immediate

  • No matter existed , there was only energy
  • The forces of the nature was all tied up together as a single force called the ‘Superforce”
  1. Gravity
  2. Strong Nuclear
  3. Weak
  4. Electromagnetic
  • At the end of this stage a key event occurred and gravity split of from the superforce.

1.2 Grand Unification Epoch

Temp : 1036 kelvin

Time after big bang: 10-43 seconds

  • The forces of nature collectively were:

Grand Unified Theory :

  1. Strong Nuclear
  2. Weak
  3. Electromagnetic
  • And Gravity( separated )
  • this epoch ended when again one of the forces ,i.e the strong nuclear force broke away.

1.3 Inflationary Epoch

Temp : 1033 kelvin

Time after big bang: 10-36 seconds

  • in this stage the universe expanded rapidly almost from a size of an atom to the size of an orange.
  • the universe at this time churned with
  • This rapid expansion increased the linear dimensions of the early universe by a factor of at least 1026 (and possibly a much larger factor), and so increased its volume by a factor of at least 1078. Expansion by a factor of 1026 is equivalent to expanding an object 1 nanometer (10−9 m, about half the width of a molecule of DNA) in length to one approximately 10.6 light years (about 62 trillion miles) long.

  • it is exactly not known when the inflationary epoch actually ended but it is estimated to occur between 10^-33 to 10^-32 seconds.
  • this rapid expansion disturbed all the elementary particles from the grand unification epoch.
  • on the 17th of march 2014 few astrophysicists announced the deflection of the inflationary gravitational waves in the B-mode power spectrum, providing the first clear experimental evidence for cosmological inflation and the Big Bang.

1.4 Electroweak Epoch

Temp : 1020 kelvin

Time after big bang: 10-32 seconds

  • The forces of nature collectively were:
  1. Weak
  2. Electromagnetic
  • Gravity( separated )
  • Strong nuclear (separated)
  • This epoch ended when the remaining two forces finally split away
  • Somehow around this epoch the matter won over antimatter and so today we are left with an universe that is comprised entirely out of matter. somehow there was just an extra matter particle.
  • By now all of the universe’s ingredients were present.
  • However the universe was still hot and dense for the formation of subatomic particles.

1.5 Hadron Epoch

Temp : 1010 kelvin

Time after big bang: 10-6 seconds

  • By this time the universe cooled down enough for the quarks to bind together to form protons and neutrons.’
  • In physical cosmology, the hadron epoch was the period in the evolution of the early universe during which the mass of the universe was dominated by hadrons. It started approximately 10−6 seconds after the Big Bang, when the temperature of the universe had fallen sufficiently to allow the quarks from the preceding quark epoch to bind together into hadrons. Initially the temperature was high enough to allow the formation of hadron/anti-hadron pairs, which kept matter and anti-matter in thermal equilibrium. However, as the temperature of the universe continued to fall, hadron/anti-hadron pairs were no longer produced. Most of the hadrons and anti-hadrons were then eliminated in annihilation reactions, leaving a small residue of hadrons. The elimination of anti-hadrons was completed by one second after the Big Bang, when the following lepton epoch began.

1.6 Lepton Epoch

Temp : 1012 kelvin

Time after big bang: 1 second

  • the above diagram shows how the forces split up from the one collective “Superforce”
  • In this epoch the protons and the neutrons underwent a significant change. They fused together and formed nuclei and in doing so the first chemical element , helium was created.

Let us please take a moment now to appreciate that only a second has passed since the beginning of everything !!!!!

more in-depth information regarding the particles can be found in the article , ” The Standard Model of Particle Physics


2.1 Atomic Epoch

Temp : 2000 kelvin

Time after big bang: 50,000 years

  • for the first time ever the universe was cool enough for electrons to attach to their nuclei
  • called recombination,this process created the 2nd element hydrogen.

2.2 Galactic Epoch

Time after big bang: 200 million years

  • hydrogen and helium dotted the universe with atomic clouds
  • within the clouds small pockets of gas may have had enough gravity to cause the atoms to collect.
  • these clusters of atoms formed during the galactic epoch became the seedling of the galaxies.
  • nestled inside the galaxies stars began to form and in doing so they formed the universes latest and current stages of development.

2.3 Stellar Epoch

Time after big bang: 3 billion years

  • the formation of the stars then caused a tremendous ripple effect which helped shape the universe as we know it today,
  • heat within the stars caused the conversion of hydrogen and helium in almost all the remaining elements in the universe.
  • in turn these elements became the building blocks of planets,moons,life and everything we see around us today.

This ecosystem is only possible because of the many stages of the universe’s development.

Now what happened right at the beginning ?

We don’t know at all what exactly happened right at the beginning.

Our tools to understand the nature breaks down, natural laws stops making sense and time itself becomes weebly wobly !

To exactly understand what happened there we need a theory that combines Einstein’s theory of General Relativity with Quantum Mechanics, something on which hundreds of scientists are already working. But this leaves us with a lot of unanswered questions.

  1. Where there universes like our own?
  2. or this is the first and only universe?
  3. what started the big bang?
  4. or did it just occur naturally ? based on the laws we probably don’t understand yet.

We don’t know yet! and maybe we never will. But we do know is that the universe as we know started and gave birth to particles,stars, clouds,galaxies,planets,moons, Earth and Us.

Since we ourselves are made up of star dust. We are not separate from the universe but a part of it. We could even say we are the universe’s way of experiencing itself. So lets keep experiencing it until we are left with no questions. Started with a Big Bang

I would highly recommend few books that would really help you know much in depth about Big Bang and much more regarding the cosmos:

  4. A Brief History of the Universe: From Ancient Babylon to the Big Bang (Brief Histories)
  5. The Physics Book: From the Big Bang to Quantum Resurrection, 250 Milestones in the History of Physics (Sterling Milestones)
  7. Cosmos
  8. Relativity: The Special and the General Theory (Routledge Classics)
  9. Black Holes: The Reith Lectures
  10. The Oxford Companion to Cosmology (Oxford Quick Reference)

please leave a comment below or ask any question you want to regarding the article “Started with a Big Bang



I am Mayukh Bagchi. 3rd year Undergraduate Engineering student at SRM University , physics and in general Astrophysics is my passion and I want to pursue the same. This blog is dedicated to serve the community with honest and clear insights to the cosmos.


Yash Dashetwar · June 16, 2018 at 5:42 pm

That was great bro..keep it up…..proud of you☺

    Mayukh · June 16, 2018 at 6:01 pm

    Thanks you Yash for your support! Keep reading and sharing your knowledge with everyone!

Vaibhav patil · June 17, 2018 at 2:38 am

That was great work mayukh!!!
It’s the Simple and best explanation about
Big Bang theory.Keep it up and best wishes for near future

    Mayukh · June 17, 2018 at 3:31 am

    Thank you so much Vaibhav ! Really appreciate the help! Keep sticking around for more content

Raghav · June 17, 2018 at 6:11 am

That’s a wonderful work brother looking forward to read more of your works!

    Mayukh · June 17, 2018 at 7:23 am

    Thank you so much brother! will definitely keep updating with more indepth content

Gokul · June 17, 2018 at 10:04 am

Wonderful article maayukh.. Keep it up 👏

    Mayukh · June 17, 2018 at 10:13 am

    Thank you so much Gokul for giving it a read! i really means a lot, hope you have taken back something from it!! keep sticking around and if you want to know on any topic, do let me know

J. Bagchi · June 18, 2018 at 7:54 am

Well done ! Really got to know something useful .

Vikas · June 18, 2018 at 3:03 pm

I appreciate Ur work mayukh. I suppose u will upload more articles like this…..😊😊😊😎😎

    Mayukh · June 18, 2018 at 4:01 pm

    Thanks You Vikas!! Means the world to me! I’m glad you liked and gave it a read and also put up a comment! This gives a lot of motivation!! Please stick around for more and keep sharing it!!

    Mayukh · June 18, 2018 at 4:02 pm

    You could also read my article on the “The Standard Model of Particle Physics” link :

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