• Question: Is it true if you send one identical twin to space and keep one on earth for a couple of years, when the twin from space comes back will it look younger than the one on earth?

    Asked by bethanyknight to Julian, Eoin on 22 Mar 2011.
    • Photo: Julian Rayner

      Julian Rayner answered on 22 Mar 2011:

      Hi bethany. I think what you are referring to is something Einstein discovered, which is that time is not a constant thing, but is relative – influenced by other factors such as motion and gravity. The faster you travel (closer to the speed of light), the more time slows down. I could be getting this wrong, but my understanding is that if one twin travelled fast enough away from earth, then they might indeed return younger than the twin that remained behind. Only trouble is that we are a long long way away from inventing anything that will make us travel fast enough for that to work. Shame, there would be queues of people wanting to travel fast enough to stay young!

    • Photo: Eoin Lettice

      Eoin Lettice answered on 22 Mar 2011:

      Hi bethany,
      This example is called the twin paradox and was described by Albert Einstein to try and explain his theory that time is relative – it speeds up or slows down depending on how fast one thing is moving compared to something else.
      Einstein thought that the faster you go, and the closer you get to the speed of light, the slower time goes by from the perspective of someone who isn’t moving (the earth twin in this example).
      It’s a theoretical example so, until we discover a way to allow twins travel at close to the speed of light, it is difficult to prove this theory.

      Eoin

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