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Could (or is) a mechanical connection be FTL?

  1. Dec 9, 2015 #1
    Say we have this scenario, we have two bodies (big rocks, asteroid etc), existing in the vacuum of space, both are in perfect sync with each other (distance between them remains static) and are 1 light second apart in distance. Bob is standing on one rock and Mary on the other. Each has a radio, but there is also a long rod made of some material we haven't discovered yet that does not bend, stretch or compress when stress is put on it. Both Bob and Mary are hanging on to one end of the rod. Bob says "hi Mary" at the exact same time he pushes on the rod.

    Will Mary feel the pressure on the rod at her end before she hears Bob say "hi"?
  2. jcsd
  3. Dec 9, 2015 #2
    If the material is made of any currently known form of matter or energy, and held together by any currently known interaction, then the push will arrive at the time the radio message arrives, or later.
    In other words, the answer to the title is No.
  4. Dec 9, 2015 #3


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    Gold Member

    To expand just slightly on Slowthinker, the speed of transmission in a solid is the speed of sound in that solid and is limited by electromagnetic interactions (atom's electrons banging into each other) and for all substances make of atoms, is approximately zero compared to the speed of light.

    This question is answered here frequently. Lots of people have this mistaken idea.
  5. Dec 9, 2015 #4


    Staff: Mentor

  6. Dec 10, 2015 #5
    If the rod is made of material that satisfies chemical physics, pressure goes as sound wave the speed of which is less than light speed. I am sorry for this boring answer.
  7. Dec 10, 2015 #6
    Thanks - all I needed to know! :-)
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