How did everything begin? It’s a question that humans have pondered for thousands of years. Over the last century or so, science has homed in on an answer: the Big Bang.
This describes how the Universe was born in a cataclysmic explosion almost 14 billion years ago. In a tiny fraction of a second, the observable universe grew by the equivalent of a bacterium expanding to the size of the Milky Way. The early universe was extraordinarily hot and extremely dense. But how do we know this happened?
Let’s look first at the evidence. In 1929, the American astronomer Edwin Hubble discovered that distant galaxies are moving away from each other, leading to the realisation that the universe is expanding.
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