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Distant Galaxies
Credit: STSci (HST)

The Universe is everything there is. It contains all the stars, planets, dust, gas, atoms, dark matterlight, and the space in between. It even includes the laws of physics, like gravity. As far as science is concerned, everything which exists is part of our Universe.

Scientific evidence tells us the Universe started with the Big Bang. This took place around 14,000 million years ago. Over time, the Universe has expanded, cooled and evolved. It now contains billions of galaxies. Each galaxy contains billions of stars and planets, plus lots of dust, gas, and dark matter. 

The Universe contains a lot of stuff, but it is also very big. This means on average, there is only 1 single hydrogen atom for every four cubic metres of volume. So the Universe is mostly made of nothing!