History of the Universe

The Universe began with the Big Bang about 14,000 million years ago (14,000,000,000 years). When it was young, the Universe was very, very hot and dense. Since then, it has been cooling down and getting bigger.
 

For the first tiny fraction of a second after the Big Bang, everything was too hot for us to describe what it was like. It was not like any physics we see or experience now. But we can use science to work out what happened from as little as 10-43 seconds - or 0.0000000000000000000000000000000000000000001 seconds! - after the Big Bang.

 

Big Bang Timeline
Credit: NSO

Up to 10-6 seconds: Lighter particles

Subatomic particles like quarks, electrons and neutrinos exist. At this point, the Universe is too hot and dense for "normal" physics to work. Even forces like gravity act in different ways. Experiments in huge particle accelerators help us work out how physics works in extreme conditions like these.

After 10-6 seconds: Protons and Neutrons created

Up until now, the only things that could exist were very light particles. Now the Universe is cool enough for heavier particles to form, like protons and neutrons.

After about 1 second: Making elements

After 1 second, things have cooled down enough for hydrogen nuclei to exist. Some hydrogen nuclei fuse together to make helium nuclei. The large amount of hydrogen in the Universe is one of the pieces of evidence for the Big Bang.

After about 380,000 years: Normal atoms created

The Universe is now cool enough for atoms to exist. Before this point, the Universe was too hot for electrons to stay in orbit around a nucleus

The atoms release extra energy as photons, or light. So this is also when the Cosmic Microwave Background is created.

After about 400 million years: The first stars

Huge clouds of hydrogen collapse under their own gravity. It is hot enough inside for the first stars to begin shining. These stars create the heavier elements we see across the Universe today.

After 1000s of millions of years: Galaxies form

Gravity pulls clumps of matter together. Huge collections of stars form the first galaxies.

About 5,000 million years ago: Our Solar System forms

Our Solar System forms from a huge cloud of dust and gas in the Milky Way. This dust and gas contains elements which were created in earlier stars. Over 99% of the cloud becomes the Sun. The rest becomes the planets and other objects of our Solar System.

Today

Today the Universe contains lots of stuff we can see. Stuff like planets, stars, galaxies, dust, and gas. It also contains stuff we can't see, like dark matter. Even after 14,000 million years, the Universe is still expanding. We do not know yet what will happen to it in the future. But astronomers are working hard to find out.