The Big Bang Theory

What do we really know about the big bang?

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The big bang theory

“In the beginning, there was nothing and then, it exploded.”

That is the most commonly known understanding of how the universe started. Although there was technically no explosion and there was probably ‘something’ in the beginning, this quote paints a picture in the minds of small children and qualified cosmologists alike, all the explanations that follow just refine that picture and form the foundation for the Big Bang Theory. 

This is the most popularly known theory for the beginning of the universe, and as we said already, most of you get the gist of it right but your understanding of the theory, most probably, is bonkers. But if it’s any consolation, no astrophysicists fully understand the theory either. There are just too many holes in our scientific theories and too many unsolved mysteries for us to properly understand the beginning of the universe. So you have been warned: there will be points in this article where we would reach dead ends in scientific knowledge, problems no one currently has answers to, and we will have to take a leap and jump to problems that we do have answers to.

What is the Big Bang Theory?

Edwin Hubble

It is a scientific model that explains the history of the universe. Edwin Hubble discovered that the universe was expanding in 1925. It doesn’t take a genius to take that information and conclude that the universe was a bit smaller last week, even smaller last year, much smaller a million years ago and extremely small billions of years ago. Big Bang, essentially, is an understanding of the universe that depicts its state in terms of how it looked like, what it contained, how big it was, depending on the time. And the theory doesn’t just help us understand the universe’s past, but also its future. It’s pretty simple, really. If you observed that a bucket of water was leaking and was half full, you can predict when it’ll be empty due to the leak. Similarly, we know that the universe is expanding and can use this information to predict its size, temperature etc. in the future.


“Big Bang” is commonly referred to as an explosion that created the universe, which only gets it half right. Yes, something did trigger the sudden expansion of the universe in the beginning but no, it wasn’t a “Bang” because there was no sound.
But most of you clicked on this article to know about the “beginning of the universe.” Unfortunately, an astrophysicist works by understanding the current state of the universe and slowly understanding its past, going further and further into the past, until they reach the beginning of the universe. So physicists have a better grip on how the universe looked a few thousand years after the Big Bang but they don’t have a very good understanding of what happened right in the beginning, and figuring that out is still a big problem. But fortunately for you, this is not a course in cosmology. It’s an article, so you can get what you want; and we will start from the beginning and move towards the present rather than go in the opposite … ehm … right direction.

What was there in the beginning?

We wrote that there was probably ‘something’ in the beginning. But what exactly was it? Was it mass, was it energy, was it both? See, we already know that mass and energy are convertible forms of each other. So … it was actually both! In fact, everything has an aspect of both mass and energy. Einstein says this in his famous E=mc^2 equation, Werner Heisenberg says this in his uncertainty theory, Max Plank says this in this quantum theory … we could go on, doesn’t matter for now. The point is that in the beginning, the entirety of the universe, mass and energy combined, was packed in a very small place the size of a full stop, more or less. Yes, the entire universe was once the same size as that of a full stop.

That means two things: 

i. One, that the universe was immensely dense and carried a lot of mass in a small volume. 

But that sounds odd, entire galaxies in a single full stop? That’s doesn’t sound possible. Guess what? It doesn’t entirely have to be that way. Which brings us to the understanding that,
ii. There was actually more energy than mass. Most of these giant planets and stars were stored in the form of energy and since energy doesn’t occupy space, you can fit as much of it in as little space as you want, even if it’s the entire universe’s energy.

Now, we are clear on what was there in the beginning of the universe. There was a bunch of extremely dense mass and energy in a very small volume. But why did it ‘expand?’ What caused the Big Bang? Why couldn’t the universe just chill without banging? To know that, it’s time to dive deeper into physics.

What triggered the Big Bang?

This is a million dollar question and absolutely no one knows the answer to that. Scientists are unaware of why the initial universe started expanding.

Was there an imbalance of something? If so, what terrible thing forced the universe to be in this dense state in the first place? Nature resists imbalances.

Hmm … maybe the universe starts compressing after it can’t expand anymore? If so, it would compress to a certain point and the Big Bang would happen. This compression is called Big Crunch and might be the real reason for the Big Bang. But unlike hard evidence of expanding universe that serves as foundation for Big Bang, we have no evidence for Big Crunch. Damn it.

Oh what about the string theory? You know what, forget about it. This is a whole different pandora’s box.
So the point is that there are different theories that can explain why Big Bang happened, but none of them have any evidence or strong proof. They are just speculations. This is currently where our understanding of nature lags behind nature itself. We don’t know why the universe started expanding. We just know that it did.

After the Bang:

Anyway, the universe started expanding and a lot of matter was created. But in the beginning, the particles of matter were extremely small and densely packed together. This means that no gases, liquids or solids cold be formed. Moreover, since sound waves propagate through a medium, this was all completely quiet. That’s why we say that there was no “Bang.” This also means that gravity largely affected these tiny particles, which is not the case in the universe right now; and that creates another big problem. Einstein’s theory of general relativity is very good at explaining how gravity works for large particles such as Sun and Earth. But it’s not very good at explaining how gravity works for extremely small particles. Quantum-gravity, is yet another mystery physicists are unable to solve. Einstein, Neil Bohr and Werner Heisenberg spent their lives figuring out how gravity could be explained for quantum particles, but they never succeeded.
Enough about gravity. With more expansion, the particles were finally far away from each other that we can predict how they behaved. At this point, the matter in the universe was a really dense and extremely hot “Plasma,” which is a state of matter in which electrons can’t revolve around a nucleus.

After some more time, the universe had cooled and expanded just enough for electrons to start revolving around neutrons and protons. This would form atoms. The first atom being that of the Hydrogen gas. We can guess that Hydrogen was the first element and the first gas ever because its atoms are small and therefore, there isn’t a lot of attractive force needed to keep the electron revolving around the nucleus. After a long time when temperatures were low enough, solids, liquids and other gases were formed. Chunks of gases, solids and liquids form everything we know. These chunks of matter moved away from rest of the matter as the universe expanded and formed stars. Pieces of these stars, when they stopped burning and cooled down, separated from them and scattered. Some of these pieces would start rotating around each other and other stars, forming moons and planets.

Just like the immediate beginning of the universe, the ultimate ending of the universe is unknown as well. Maybe, the Big Crunch is true and the universe will expand and compress forever. Maybe, the string theory is true and there are infinite universes. Maybe, the universe will just disintegrate and freeze in the future, expanding forever.

Test yourself - The big bang

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I'm a Mechanical Engineer, and an entrepreneur. I believe that science and engineering is a way of communicating with nature and reality. Unfortunately, our education system fails to incite 'intrigue' and 'curiosity,' we are flooded with information we don't understand. I write to educate students and to help them love the reality around them.

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