• Question: How do we know when the Big Bang occured?

    Asked by thomasrhodes to Viv, Asif, Laura, Lena, Sean on 12 Mar 2012. This question was also asked by dawarboss.
    • Photo: Viv Lyons

      Viv Lyons answered on 12 Mar 2012:

      One of the methods used to work out the age of the universe involved looking at the expansion of the universe and extrapolating backwards. Astronomers have used shifts in the wavelength of light coming from other galaxies to determine that everything in the universe is accelerating away from everything else. It looks to us like everything is moving away from us but only because we happened to feel like we are stationery. In fact we are moving too. A good way of imagining this is drawing dots on a balloon. As you blow up the balloon all the dots separate away from each other but none of them are at the centre.
      Observation has shown that the further a galaxy is from us the faster it is moving so if this is traced backwards in time astronomers have worked out when everything was in the same place, i.e. when the big bang occurred, about 13.7 billion years ago.
      There are a couple of very cool pictures taken by astronomers of some very early galaxies that are the farthest objects we have managed to see and therefore must be the youngest (http://hubblesite.org/newscenter/archive/releases/2004/07/). It is mind-boggling to think that when the light we see now left them our solar system, let alone our planet did not even exist.

    • Photo: Sean Murphy

      Sean Murphy answered on 19 Mar 2012:

      This is a good question! Astronomers use very large telescopes to look at light from very far away. Because light travels at a known speed, we can work out from the distance it has traveled how long it has been traveling. It is quite difficult to explain how they do this and I think Viv has done a good job!

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