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Speed of light travel

  1. May 21, 2009 #1
    Ok, I have come up with a new theory of traveling at the speed of light. This is totally theoretical and isn't phesable at any level. That aside, here it is.

    Make a pole 1000 light years long. Now swing the pole like a bat. The tip of the pole should be traveling millions of times faster than the speed of light.

    Again, this is theoretical. You can assume that the pole is strong enough to stand the length without snapping. Lets say the pole's total mass is 1 pound. Would this work? Please explain.

    Yes, I know about E=mc[tex]^{2}[/tex]
  2. jcsd
  3. May 21, 2009 #2
    No, you can't, which is exactly why your theory doesn't work. Nothing is infinitely rigid.

    If you would swing a pole of that length at that speed assuming it won't break, it would bend. It would bend just enough so that the tip would still not travel at the speed of light. You cannot assume that it doesn't bend, because that would imply it was infinitely rigid.
    Simply speaking; if you imagine the pole as a large row of atoms/molecules gripping on to each other. If you swing your pole, the atoms nearest to you would swing nearly instantly. But the atoms at the end of the pole would not feel anything; that is, until the 'shockwave' of the sudden movement reaches them. This shockwave travels at the speed of sound in the pole, which is not faster than light.

    Also, this isn't a new theory, it is probably one of the most thought up 'experiments' to have something move at the speed of light.
  4. May 21, 2009 #3
    The pole consists of atoms that interact with each other via local interactions. So picture a lattice of atoms such that if you deform the lattice the atoms can move bumping into the neighboring atomes thereby propagating the deformation throughout the lattice.

    If you push some supposedly rigid structure, then what really happens is that one side is squeezed and that compression wave propagates to the other end. This happens so fast (at the speed of sound), that it looks like it is intantaneous.
  5. May 21, 2009 #4
    So the pole would bend so that nothing would be traveling at the speed of light? I also figured that this theory has already been thought of.
  6. May 21, 2009 #5
    Yes, and there is no way to avoid that without assuming infinite rigidity.
  7. May 21, 2009 #6
    Ok. New question, what is rigidity?
  8. May 21, 2009 #7


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    Staff: Mentor

    Exactly. It would coil itself into a spiral as the force propagates along the rod at the speed of sound. You can simulate the effect by spraying a garden hose while spinning in place.
  9. May 21, 2009 #8


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    Staff: Mentor

    More commonly known as stiffness. Stiffness is a function of elasticity and moment of inertia (geometry): http://en.wikipedia.org/wiki/Stiffness

    Stiffness is a static property. When you apply a quick force, the situation becomes dynamic and the mass factors in. Together, these factors determine the speed of wave propagation (sound) in the object.
  10. May 21, 2009 #9
  11. May 21, 2009 #10
    If nothing is infinitely rigid , what if we used an electron positron pair that were entangled and separated them by 10 light years and then rotated that would that work .
    or if we had the electron positron pair that were entangled and we rotated one of them counter clock wise and the other one rotated immediately that would be faster than light .
    or the Path integral formulation of quantum mechanics where light takes all possible paths and it get there in a time faster than c for certain paths how do we explain this .
  12. May 21, 2009 #11


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    Gold Member

    You misunderstand what entanglement is. It does not mean they are locked together in any fixed way.
  13. May 21, 2009 #12
    oh i see
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