• Question: What exactly is time dilation?

    Asked by jeremyhatt to Ben, Dave, Ed, Sam, Susana on 19 Jun 2013.
    • Photo: Benjamin Hall

      Benjamin Hall answered on 19 Jun 2013:

      Time dilation is the difference in time between one thing happening and another thing happening when percieved by two different observers.

      So if I was standing on a train station platform watching a clock on a train, and you were sat watching the clock whilst sat in the seat in front of it, the difference in time between one ‘tock’ of the clock would appear greater to me than it would to you. This is because when things that are moving are observed from an object that isn’t moving, they happen more slowly.

      This is because of the nature of the space-time continuum and I’m afraid my physics isn’t up to scratch to explain it in any more depth.

    • Photo: David Briggs

      David Briggs answered on 20 Jun 2013:

      Time dilation is the distortion of space-time, mostly by gravity.

      Einstein came up with the idea of space-time – that space and time are essentially the same thing, and both can be affected by gravity.

      Really massive objects like Stars and Black holes have strong gravity can influence the passage of time around them. Time passes more slowly in a gravity field – so it you took two clocks, put one on the desk, and took the other to a black hole, the one near the black hole would slow down (compared to the other one) the closer you got to the black hole. When you got to the event horizon, the clock would stop — compared to the other one.

      Time wouldn’t stop for you, but if you could then go back to your clock on your desk, the black hole clock wouldn’t have moved as far as the one on your desk.

      Strange huh?

    • Photo: Susana Teixeira

      Susana Teixeira answered on 20 Jun 2013:

      Time dilation tells us about how time can be measured differently by 2 different observers, if they are moving with respect to one another. Time and space are not independent!

      It is usually not something that affects us, because we do not travel at speeds close to the speed of light. At this sort of speeds time is “dilated”, or in other words it appears to stretch for someone travelling at that speed. Like if Ben’s train was going very very fast, for someone sitting inside the train watching their own wrist watch. Time would pass slower for the train passenger than for the person watching the train whoosh past.

    • Photo: Sam Horrell

      Sam Horrell answered on 21 Jun 2013:

      So as Ben and David have said its is the distortion of time by gravity.

      A couple of interesting things that have come about from this. GPS satellites up in space are affected less by the gravity of the earth so they can go out of sync very very very slightly because of the time dilation. However, this tiny fraction can throw a satnav off by a good few miles so they have to correct for this.

      Also, it means that your head is slightly older than your feet because your feet are closer to the earth so times moves more slowly. Only by tiny fractions of a second though.

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