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Direction of Motion and Time

  1. Jun 18, 2012 #1
    I was watching the Brian Greene program, called Illusion of Time, on NOVA and saw the part on direction of motion and time. If you are very far away from an object and move away from it, you will be in your present but that object's past. If you move towards the object, you will be in your present but the object's future. Can someone explain why direction of motion affects time in this way?
  2. jcsd
  3. Jun 18, 2012 #2


    Staff: Mentor

    The short answer is that Greene is here using the terms "past" and "future" in a way that doesn't match up well with our common intuitions. When he says that you are in another object's "past", he does not mean that you can actually do anything to change the way the object is "now"; and when he says that you are in another object's "future", he does not mean that you can actually get any information from it as it is "now". So you can't actually change anything about the other object by changing your state of motion.

    The longer answer requires understanding the math behind special relativity and spacetime, which may be more than you want to get into.
  4. Jun 19, 2012 #3

    You can see in above image that B is going far from A. So, B's Line of present touches to A's past. And C is coming near to A. So, C's LoP touches to A's future.

    But, this is just the game of words. C cannot see A's future before A. B cannot do anything in A's past to affect A's present.

    Light ray coming from event D and E will take some time to reach to B and C. There is nothing like instant.
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