The Big Bang

“Even though we call it a ‘Big Bang’ nobody believes that it started off with a bang,” astrophysicist (a scientist who studies the stars and the universe) Dr Maggie Lieu tells Science+Nature. The creation of the universe was less like an explosion and more like a balloon being blown up very fast.

If the most important event in the history of everything happened 13.8 billion years ago, before anyone was around to see it, how on Earth can we know what happened at all? Luckily, clues are everywhere – even in you.

Cosmic drift

Almost 100 years ago, astronomer Edwin Hubble noticed that galaxies appeared to be running away from us. Everything in space is rushing apart.

Experts pressed rewind. If everything is moving apart now, it must once have been squashed together. Every star, every galaxy, and every atom in the universe once existed in a speck smaller than this full stop. It’s the drifting apart of all that matter that experts call the “Big Bang”.

But if there was no bang, where did it get its name? Astronomer Fred Hoyle hated the idea and poked fun at it by naming it the “Big Bang”. He thought elements like carbon could never have been created like that. He was right. Astrophysicist Ethan Siegel told Science+Nature that Hoyle “pretty much invented” the science behind how stars make carbon. But about the Big Bang, Hoyle was wrong and he refused to change his mind.

Load of poo

But if the universe began as a tiny, hot speck, surely some of that warmth must be left today?

Experts call it “cosmic microwave background radiation” and it was discovered by accident. In 1964, two scientists were using a giant horn-shaped antenna when they noticed something was off with their signal. They blamed pigeon poo! Scrubbing it away made no difference. The hiss they were hearing was the afterglow of the Big Bang.

Elements we see around us today – hydrogen and helium – were both cooked up by the Big Bang and are also still around us in the same mix. Even inside of you.

Before and after

Looking into space is also looking back in time. Light takes time to reach us so the further away we see, the further into the past we see. The James Webb Space Telescope is just one of the tools scientists are using to try and answer the question of how the universe was made.

But ask what came before the Big Bang or what caused it and even experts are stumped. “This is where all the physics that we know breaks down” says Maggie. “All that matters is the evidence we get from the universe,” says Ethan.

There’s one final twist. Some scientists think that at some point the universe will start to rewind and that everything will once again crush together into a tiny dot. Experts call it the “Big Crunch.” But others aren’t so sure, thinking that one day the energy of the Big Bang will run out and the universe will eventually cool down and die.

In the 1990s, telescopes revealed that the expansion of the universe isn’t slowing down but is instead speeding up, like a mysterious force is pulling it apart. Scientists have named the force “dark energy” – but nobody knows what it is yet…

Also

The universe features so many big numbers that making sense of them can be tricky. Famous scientist Carl Sagan came up with a clever trick.

If you were to squeeze the 13.8 billion year history of the universe into a single year with the Big Bang on January 1st and today on December 31st, the Sun and Earth are born in September and dinosaurs turn up around Christmas time.

Everything in every history book you’ve ever read has happened in the last few seconds.

First published in The Week Junior Science+Nature, issue 104, September 2026.