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Homework Help: Special relativity

  1. Jun 20, 2009 #1
    (1) A very long stick is used in an attempt to send messages faster than the speed of light by tapping Morse code on a distant observers forehead. Why will this attempt fail to send messages faster than the speed of light?

    (2) An observer is born (event1), sits in the same place for 100 years, then dies (event2). Determine the interval between events 1 and 2. Is this a time-like, space-like or light-like interval? Can the two events be seen to be simultaneous in a different reference frame? Explain.

    As for (1) I know that it can't but for the exact reasoning I don't really have a clue besides that nothing can travel faster than the speed of light.

    For (2) I have no Idea. (However I don't think they can be seen to occur simultaneously as they occur in the same position.)

    I'm sorry for being so vague and unclear but I have read through multiple texts and just cant seem to grasp this. Numerical questions I can handle but explaining the concepts does my head in. So any help or explanations would be VERY much appreciated.
    Last edited: Jun 20, 2009
  2. jcsd
  3. Jun 20, 2009 #2
    1. lol is funny, i suggest that when the morse code is tapped, the sound is much much slower then light, so light would be faster, compared to the how fast you hear the tapping... im not sure, just an idea.

    2. the events are timelike, since they only depend on time, and i dont think they can be simultaneous
  4. Jun 20, 2009 #3
    for (1) if the stick is infinitely dense shouldn't the tap at one end be transmitted instantaneously to the other?
  5. Jun 20, 2009 #4


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    No. A shock wave travels at less that the speed of light even if density (or "stiffness") approaches arbitrarily large values in the limit.
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