How long ago was the Big Bang?

Dr Stephen Curran, from Te Wānanga Matū—School of Chemical and Physical Sciences, answers:

"The Big Bang was 13.8 billion years ago.

"We get that number by the fact that the universe is expanding so when we look at galaxies, they’re all moving away from us and that’s true of every point in the universe. So, if you imagine the surface of a balloon with galaxies drawn on and you inflate it, they’re all moving apart from each other. But if you wind that back to when they were all together it was about 13.8 billion years ago.

"So, there is something called a cosmic calendar where the entire history of the universe is squeezed into one year. So, if you have the Big Bang at one new year then all of human civilisation appears at 30 seconds to midnight on the 31st of December. So, compared to us that’s a very, very long time.

"People often ask what came before the Big Bang and no one knows, and it’s possible there was nothing, which is very hard to explain because both time and space were created with the Big Bang and so now you are getting very metaphysical. So, it’s not that the universe appeared in space, after some time it just started expanding. That is when everything was created so that’s a by definition the universe.

"So, asking what was before the Big Bang is not really something scientists can answer."