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Homework Help: Why does time and space have to be relative?

  1. Sep 18, 2012 #1
    The lorentz-transform shows that both length and time are relative concepts.
    My question is: Why does both time and length have to be relative? Why can't you mathematically construct a transform which transforms your x' relative to x such that light has same speed in both the x and x' frame while still keeping time an absolute quantity?
  2. jcsd
  3. Sep 19, 2012 #2

    Andrew Mason

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    Measurement of a distance requires simultaneous measurements of two different points in space. The reason distance measurements are not the same in all inertial reference frames (IFORs) is because observers in different IFORs do not agree on what is simultaneous.

  4. Sep 23, 2012 #3
    You can, and it was considered, but that is not sufficient.
    We discussed this in the recent (and still open) discussion thread here:

    This is specifically addressed in post #20 and following posts:
  5. Sep 23, 2012 #4


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    Say event A is light being emitted from a flashlight and event B is the light entering your eye. In the rest frame, the distance between your eye and the flashlight is x, so the time it will take for the light to propagate from A to B is x/c, where c is the speed of light. In the moving frame, x' is the distance between the two events. If x' is different and you insist c remains the same, can the time interval between A and B remain unchanged?
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