Big Bang 101: How a universe formed from nothing

Updated: Dec 23, 2020

Evolution has engineered human beings to think, to contemplate, be curious and ask questions. We base our entire existence on asking questions. All our discoveries and innovations came to us because we had questions about everything; Many of those questions solved a plethora of problems.

There does not exist a human being who hasn't contemplated the existential questions like, What is this vast expanse called the universe? Why do we even exist? Does all of this have a meaning? How did we all end up here?. For most people, these questions are spiritual. But for some of us, these questions are scientific.

Even if the open windows of science at first make us shiver ... in the end, the fresh air brings vigour, and the great spaces have a splendour of their own.
BERTRAND RUSSELL, What I Believe

Some of us reconcile with the fact that the universe is the way it is whether or not we like it. For those who prefer the brute facts of science, it does not disappoint. Science tells us that the universe came from almost nothing as a quantum fluctuation, with a big bang. Big Bang is the only theory of the universe supported with evidence. Let's take a deep dive into what we know about the origin of the universe.


A brief history:

Till the 1920s, scientists including Albert Einstein believed the universe was static, eternal and comprised a single galaxy called the milky way; surrounded by an infinite, dark and empty space. But general relativity later painted a new picture of the universe even Einstein himself could not believe. Now almost everyone knows that our universe is expanding and our galaxy is one among 400 billion galaxies in the observable universe.

Soon after general relativity got published by, scientists started applying relativity to real-world problems. When Karl Schwartzchild adopted those equations for point masses with infinite densities, it led to the discovery of black holes. Alexander Friedmann, a Russian cosmologist and mathematician, developed the Friedmann equations from Einstein field equations, pointing that the universe might be expanding in opposition to the static universe model favoured by Albert Einstein.

In 1924, American astronomer Edwin Hubble; based on astronomical observations proved that the universe was expanding.

Studio Portrait of Edwin Powell Hubble. Photographer: Johan Hagemeyer, Camera Portraits Carmel. Photograph signed by photographer, dated 1931
Edwin Powell Hubble

In 1931, Georges Lemaître went beyond just an expanding universe and suggested something extraordinary. If we extended the expansion backwards in time, it would lead us to a smaller universe with mass concentrated into a single point. He called the early universe a primaeval atom, from which the fabric of space-time came into existence.

But how does this Big Bang work? How can something come from nothing? Before that, there are a few clarifications to make.


A few clarifications:

  • First, the Big Bang was not an explosion; names can be misleading. It was the space itself expanding everywhere all at once.

  • The universe started extremely small and rapidly expanded to the size of a watermelon.

  • The universe did not and is not expanding into anything, but the fabric of space itself is stretching. The universe cannot do so because it has no boundaries.

(For example: Imagine a balloon with small dots sketched on it; when you inflate the balloon the dots get bigger. It's not because the dot has expanded but the area where the dot sits has expanded, making the dot look bigger. Same way, space itself is expanding sweeping all the galaxies along with it)

  • There is, by sense, nothing outside the universe because the universe is all there is.

  • Asking 'what exists before the big bang?' makes no sense at all.

Singularity :

As per observations of scientists, the universe started from an infinitely hot and dense gravitational singularity. We know little about this singularity. It requires both General relativity and Quantum mechanics combined to understand this singularity state. As we learnt in our previous post about gravity, Scientists are struggling to bring General relativity and Quantum mechanics into one fold.

Singularities exist in the centre of black holes.


The Plank Era:

We know the period between 0 to 10^−43 seconds into the Big Bang as the Planck epoch. During this phase, the four fundamental forces (the electromagnetic, the strong nuclear, the weak nuclear and the gravitational force) combined into one.

In this stage, the universe was only about 10^−35 meters wide and had a temperature of roughly 10^32 degrees Celsius. At 10^−43 seconds, gravitation separated from the other forces and the universe cooled down a bit. The universe was pure energy at this stage; it was ragingly too hot for any particles to form. Matter and energy were not just theoretically equivalent but were practically the same stuff.

Equal amounts of matter and Anti-matter (yes they are real!) pairs formed and annihilated each other.

At a point, slightly more matter particles formed than antimatter and couldn't annihilate as they didn't have pairs to do so. Those loners served as the ultimate source of matter to create galaxies, stars and planets.

Please take a moment to relish that by now, only one second has passed since the beginning of everything.

For the next several billion years, the expansion of the universe gradually slowed down
The Big Bang Expansion

Big Bang Nucleosynthesis:

As the universe expanded and cooled, it needed to hit a sweet spot to facilitate the formation of elements. If too hot, the atoms formed would instantly tear apart; too cold, no reaction would take place. Between 10 to 1000 seconds after the big bang, the temperature dropped one billion degrees to 100 million degrees Celsius; the sub-atomic particles such as protons, electrons and neutrons formed in its hot forges.

The nuclear fusion reaction we all learnt in 8th grade is enough to understand the formation of atoms during the big bang. Nuclear fusion reaction takes place inside every star; it's a process in which two light nuclei combine to form a heavier one, releasing an enormous amount of energy.

As we read in the 'life cycle of stars', fusion not only creates energy but it also additional elements.

As the cosmos continues to cool—dropping below a hundred million degrees—protons fuse with protons and with neutrons, forming atomic

nuclei and producing a universe in which ninety percent of these nuclei are hydrogen, ten percent are helium, along with trace amounts of lithium.


None of the elements that facilitate life formed in the Big bang; the carbon in your body, the oxygen you inhale, the metals in your kitchen tableware and the uranium used in nuclear power stations—was all once forged in the fiery furnaces inside stars. We are star-dust!

Following nucleosynthesis, the universe existed as a hot, dense plasma of atomic nuclei, electrons and protons. The light could not pass through this hot plasma; any atom that formed got ripped apart. This state continued for 3,80,000 years.



Recombination and the cosmic microwave background (CMB):

Magic happened when the temperature of the universe fell below 3,000 degrees. The phase called recombination allowed electrons to bind with the nuclei forming the first-ever atoms. The universe became transparent when the last scattering took place. The photons trapped within the hot dense plasma freed themselves and traversed across space.

Astronomers can see this light from the early universe that is virtually unchanged for over 13.5 billion years today. This super-cooled microwave radiation called the cosmic microwave background is just 2.73 degrees above absolute zero (-270 degrees).

Robert Wilson and Arno Penzias of Bell Laboratories, New Jersey accidentally discovered this leftover radiation from the Big bang while they were trying to eliminate a faint cackle caused by it.


The photons from the big bang are all around us. The cosmic microwave background accounts for 99.99% of radiation in the entire universe. For every photon produced in a star, there are 10^32 photons left over from the big bang.

If someone tells you that they don't believe in the Big bang, tell them there is proof right in front of us. We see the Big bang!

(Feel free to use our infographics for educational purposes or share in social media. Don't forget to credit us with a link)

Pre-Big Bang-A Universe from Nothing:

The idea for the universe created from nothing lies in the quantum realm. It suddenly appeared where once there was nothing at all.

Sub-atomic particles can blink in and out of existence all the time. Their sudden, almost magical appearances have a price to pay; greater the energy of the particle formed, faster it disintegrates. That is more energy borrowed, shorter the life.

Nature plays with strict rules here. If you borrow energy, you need to give it back; if not, you die. Higher the sum you borrow, shorter gets your life. But if we borrow nothing, it's a different story altogether.

According to the law of conservation of energy, the overall energy of the universe sums to zero.

If we borrow no energy at all, a universe in principle can pop into existence from nothing.

Allen Guth, the proprietor of the theory calls it the free lunch universe.

It formed from nothing as a quantum fluctuation; such a universe should have collapsed under its gigantic gravity and soon disappeared. But before that could happen, a grand expansion came to the rescue and pushed it out of the quantum realm before it had any chance to collapse. A universe can create itself from nothing without violating a single law of physics.



Structure Formation:

During the first billion years, the universe further expanded, and the temperatures cooled down a bit. The matter that existed here and there clumped together and gravitated into the colossal groups we now call galaxies. Nearly a hundred billion of them formed, each comprising hundreds of billions of stars that undergo thermonuclear fusion in their nuclei.

(Learn more about the formation of stars here) For the next twelve billion years, the expansion of the universe steadily slowed down as the stuff in the universe pulled on itself through gravity.

Some stars, with more than about ten times the mass of the Sun, produce enough pressure and heat in their cores to manufacture heavier elements, those makeup planets and the life that may thrive upon them.

Reasons to believe in the Big bang theory:

Even though not all the scientists of the 21st century agree that the big bang is how the universe formed, it is still one of the most plausible explanations we have. Here's why.

  • Our microwave telescopes detect background radiation, surrounding us on all sides and virtually perfect and consistent in all directions. It is red-shifted light from a period almost as primitive as the cosmos itself.

  • We can see that the universe is expanding and moving apart, which means it was once much tinier and denser. Physicists and astronomers can determine how fast things are moving apart, and calculate how long before that microscopic, dense state existed.

  • We find Quasars in the galaxies far away from us; light from quasars light up all the stuff in its path, giving us insight about the early universe. In 2011, astronomers found clouds of primordial gas by investigating distant quasars. These two clouds of gas contain only hydrogen and deuterium, but no traces of heavier elements; they likely formed in the first few minutes after the Big Bang.

What the Big bang theory not explain?

Even though Big Bang theory is one of the ablest cosmological theories, it has its gaps to fill.

  • Big bang tells us that the universe expands from a gravitational singularity. But it does not explain the origin of this state of singularity. We do not know what existed before the singularity.

  • The universe seems to have expanded from an exceedingly orderly, smooth state. We can see this through the uniformity of the cosmic microwave background. We don't know why this is the case.

  • Understanding space and time fully compels us to discover equations that can grapple with the extreme conditions of immense density, energy, and the temperature of the early universe. Many physicists believe, developing a unified theory of physics will resolve this quest.



Research and references:

1. Krauss, Lawrence M. (2012). A Universe from Nothing: Why There Is Something Rather Than Nothing. New York: Free Press

2. Parson, Paul (2018). The Beginning and the End of Everything: From the Big Bang to the End of the Universe, Michael O'Mara Books, 2018

3. Big Bang From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Big_Bang

4. Niel Degrasse Tyson, "ASTROPHYSICS FOR PEOPLE IN A HURRY". Kirkus Reviews. March 7, 2017. Retrieved August 5, 2017.

5. A BRIEF HISTORY OF TIME From the Big Bang to Black Holes. By Stephen W. Hawking. Illustrated by Ron Miller. 198 pp. New York: Bantam Books.







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