• Question: Is Time Travel Really Possible?

    Asked by 699mndp42 to Stephen Hawking on 22 Nov 2018.
    • Photo: Stephen Hawking

      Stephen Hawking answered on 22 Nov 2018: last edited 26 Nov 2018 8:31 pm


      Hi 699mnpd42,

      Probably not 🙁

      If we look at the maths, there’s a term in relativity that looks a little like this:

      Time = 1 ÷ (1- (v÷c)) (Time dilation equation)

      Where v = velocity, c=the speed of light

      This means as we go faster the slower we appear to the universe. Once we hit the speed of light (v = c), it would be like time had stopped! If we could somehow go faster than the speed of light (v>c) it would be the same as going backwards in time (the equation becomes negative).

      Here’s the problem. We know from Einstein’s famous equation (E=MC^2), that anything with mass is limited to travelling less than the speed of light (v<c). Humans have this horrible feature, we're made of stuff and stuff has mass.

      There are a few cool tricks in quantum mechanics though. For example, a positron can be treated as an electron travelling backwards in time! This helps when predicting particle behaviour, but we don't have any anti-particle humans to test that on yet.

      So unfortunately, we probably won't be able to go backwards in time, but knowing this lets us test the limits of physics in our Universe!

      Brilliant Question

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