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Slowing gravity?

  1. Aug 23, 2003 #1
    Gravity is supposed to propogate at the speed of light; but is there any way to slow it down "in a medium" as light can be? Are gravitons (theoretically) supposed to be emitted and absorbed by masses the way photons are by atoms? If so, could something like a star cluster act in the same way a medium does for light to "slow down" gravity (i.e. take a gravitational signal, with all the absorbing and reemitting, longer to travel from one side of the cluster to the other than if no masses were present)? Or am I completely off here?
  2. jcsd
  3. Aug 23, 2003 #2


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    One of the predicted properties of gravity waves is that they are not interfered with by passing through obstructions between the source and the observer. This is one of the many reasons why astronomers are so keen on developing ways to detect them. If this property proves true, then it would seem to suggest that the waves cannot be "red-shifted", slowed, or weakend by any medium. This is only my reasoning on the matter, and there may be more reliable information at MIT's LIGO Website .

    Although this does raise the question of whether or not they can be interfered with by other gravity waves. Never thought of the idea of gravity wave interferometry before, but I'm sure I'm not the first. Must go search.
  4. Aug 23, 2003 #3
    This is a point I'm not clear on: are gravity waves the same things as gravitons? I know there are projects like LIGO and VIRGO (and maybe LISA someday) to detect gravity waves directly (and that Nobel prize from ten years ago that involved the indirect detection of them) but when a gravity wave is definitely detected will that be the same as saying gravitons have been detected? I've seen people refer to them as if they're the same but they sound like two different things to me.

    But, regardless, are gravitons emitted and absorbed by masses in any way analogous to the way photons are?
  5. Aug 23, 2003 #4


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    Gravitons and gravity waves bear the same relationship to each other as photons and electromagnetic waves do. They are the quantum and classical representation of the same thing.

    I think what gets confusing is when people refer to the graviton as the force-carrying particle for gravity.

    This is not strictly true. The force carrying particle for gravity would be the virtual graviton. In the same way, virtual photons mediate the electromagnetic force.

    so it goes like this:

    for light
    wave: electromagnetic
    particle : photon
    Field: electromagnetic
    Force carrier : virtual photon

    for gravity
    wave: Gravity
    particle: graviton
    Field: Gravitational
    force carrier: virtual graviton

    In classical terms one usually refers to waves and fields, in quantum terms, particles and virtual particles.
  6. Aug 23, 2003 #5
    I don't think gravity waves could be slowed down. Gravity waves by their nature would be propogations of a space/time wave. Much like light does not require a medium to move in, but particles will make it slow down, since gravity is the very essence of a spacetime disturbance, one would have to put the wave in something other than spacetime...but if you can find one of those, I'll give you an infinite amount of money.
  7. Aug 23, 2003 #6
    All right, thanks for the responses. Too bad to hear there's no gravitational analogue of Cherenkov radiation.
  8. Aug 24, 2003 #7
    There wouldn't be unless, as I stated, you managed to make a gravity wave move in something other than spacetime. And as I stated, if you do, please by all means contact me. You'll get an infinite amount of money hehe.
  9. Aug 30, 2003 #8
    Light is slowed down by gravity, and I can think of nothing that can slow down gravity...
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