• Question: Is time travel possible?

    Asked by danniella1588 to Colm, Eoin, Joseph, Lauren, Stephen on 18 Nov 2013.
    • Photo: Joseph Roche

      Joseph Roche answered on 18 Nov 2013:

      Not yet. But let’s not rule anything out. It may be possible in the future. Although if it does become possible in the future, surely I would have come back in time and edited this answer 🙂

    • Photo: Eoin O Colgain

      Eoin O Colgain answered on 18 Nov 2013:

      Yes, in many different ways, some of which may be science fiction 🙂

      Physicists think of space and time in a unified manner. We have 3 spatial dimensions and one temporal direction (time). Together these form a 4-dimensional spacetime. However, if one was to plot the movements of a particle or person in this spacetime, they can only move forward in time. However, the rate at which one goes forward in time can change. This can be regarded as time travel.

      We know from Einstein’s theory of special relativity that “moving clocks run slow” (we also call this time dilation). So, if we take two clocks, one at rest and one in motion, the clock in motion will experience less time. At the speeds we encounter everyday, these effects are very small, but they can become very significant if one goes quicker.

      This effect is very pronounced for muons produced by cosmic rays. Rossi and Hall (1941) noticed that if one measures muons at the top of a mountain and again at sea level that they decay slower than expected. In effect, time as measured by the muon runs more slowly!

    • Photo: Stephen Scully

      Stephen Scully answered on 18 Nov 2013:

      Yes. You are travelling into the future right now. Einstein showed that when we move through space be slow time down for us. This means that we age slower than a person who is standing still. Unfortunately in order to get far into the future we need to travel close to the speed of light. This is not possible for us yet.

    • Photo: colm bracken

      colm bracken answered on 18 Nov 2013:

      Yes, time travel into the future has already been happening for some people. The astronauts who have spent time on the space station has travelled into the future by as much as a second or two. Einstein’s theory of general relativity tells us that if you are in a stronger gravitational field then time travels slower for you than it does for someone in a weaker field. But his theory of special relativity tells us that if you are moving really fast compared to someone else then time also goes slower. Astronauts are moving at such high speeds that time goes slower for them. So when they return to Earth it is like everything here is a tiny bit older than it should be , or a tiny bit in the future. This is real effect that is agreed upon by pretty much all physicists.
      Time travel into the past is a little trickier. But since time is relative then you could argue that the astronaut stayed in the right time and everything else moved backward in time. It all depends on your perspective!

    • Photo: Lauren Mc Keown

      Lauren Mc Keown answered on 20 Nov 2013:

      To travel into the future, we need to travel at the speed of light, or at a “relativistic” speed. Which would probably kill us as we would burn up in doing so. Sure the tiles on the space shuttle had to be changed with great difficulty as they kept getting too hot on re-entry into the atmosphere…so I don’t think we will have a solution to this problem any time soon.

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