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Can information travel faster than light?

  1. Feb 23, 2008 #1
    Theory of Relativity says nothing can exceed the speed of light. My question is:
    Can any information be made to travel faster than 'c'?

    suppose, i have a light torch of very high intensity which can be rotated on an axis(its stand). the light is made to fall on a wall(extending for millions of miles). the wall itself is millions of miles away from the light torch. now if i rotate the torch on its stand, the bright spot on the wall travels very fast. and, even for very minute changes in the angle, the spot travels thousands of miles. Can spot of light on the wall travel faster than c?

    If yes, doesn't it violate our laws?
  2. jcsd
  3. Feb 23, 2008 #2

    Doc Al

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    Staff: Mentor

    Sure, why not? Note that the moving spot of light is not a physical object (it's not really any kind of "object") and that it can't be used to send a signal (thus transmit information) between one spot on the wall and another.
  4. Feb 23, 2008 #3
    Doc is right but what youre describing isnt breaking the SoL limit because it doesnt exceed it in any way.

  5. Feb 23, 2008 #4


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    Your example is similar to waves approaching a beach, not quite head on.
    The point where the wave breaks on the beach moves along the beach at great speed,
    but is not the motion of anything physical.
  6. Feb 23, 2008 #5
    To send information you must be able to produce two different results on receiving point that are consequences of choices you made.
    In your experiment this is not possible: a person standing near the wall could do nothing to influence the traveling of the illuminated spot.
  7. Feb 23, 2008 #6
    Say we have two points on the wall (A and B) that are 10 light years apart. You are 6 light years from both A and B forming a triangle. If your laser is pointing at A and you start to turn the laser it will be 6 light years before the spot on the wall even starts moving. Now you turn your laser "instantaneously" to point in the direction of B. The photon leaving your laser that is now pointing at B will take 6 light years to arrive at B so the total time from when you decided to start turning the laser to the time the signal arrives at B is 6 years. Now if you see A launch a death ray towards B it will be 6 years before you are even aware that A has launched the death ray and another 6 years before your signal to warn B that he has an incoming attack. Your alert signal to B will arrive 2 years after he has been fried to a crisp by the death ray from A. :P
    Last edited: Feb 23, 2008
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