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Superluminal transfer of information via gravity

  1. Jul 5, 2009 #1
    it takes light about 8 minutes to reach earth from the sun, and I've heard it said information cannot be transmitted faster than the speed of light. if the sun blinked out of existence, steady stream of light indicating to you the the sun still exists would last for 8 minutes, but could you not tell the sun was gone almost instantly by the loss of gravity from the sun?
  2. jcsd
  3. Jul 5, 2009 #2
    The gravitational field also has to travel at the speed of light. The gravity you feel now from the sun is pulling you towards where it was 8 minutes ago.
  4. Jul 5, 2009 #3
    jdog has given you the 'popular' reply, but it has not been proven to my knowledge, however, I don't think we would know it even in 8 minutes. Why would we? The earth would start to move straight instead of in an ellipse. How would we know that?
  5. Jul 6, 2009 #4
    star positions, communications satellites breakdowns
  6. Jul 6, 2009 #5


    Staff: Mentor

    In 8 minutes the earth would be less than 700 meters out of place. Do you really think we could detect that small an error in the star positions in less than 8 minutes? I don't.

    Communications satellites would be fine too.
    Last edited: Jul 6, 2009
  7. Jul 6, 2009 #6
    if one were looking for it yes, it would be a sad indication of mans scientific achevment of we couldn't considering star positions have been one of the strongest underlying themes in all of science reaching as far back the first humans, if we can't predict with a high degree of accuracy the path of the earth's orbit and when its no longer obeying laws by which we predict its orbit then I suggest the hope for the discovery of a fundamental theory of the universe is far beyond our scope, and moreover and more importantly one could design experiments to test for the speed of gravity, the real issue, which I am inclined to believe they have. Does anyone know of experimental evidence one way or the other?
  8. Jul 6, 2009 #7


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    Staff: Mentor

    Huh? That's just a big load of crapola. The largest stellar parallax we can see is about 3/4 of an arcsec over the course of a year. We certainly wouldn't be able to detect it to as we moved out of position 700m! (That would imply we could measure it on a minute-to-minute basis, as the earth rotates fast enough for a 700m shift in a minute at moderate latitude.

    Perhaps you are confusing this concept with celestial navigation, for which we could probably with high quality instruments and a stationary platform get closer than 700m, but it wouldn't be easy. That kind of accuracy on a ship, on a regular basis, would be nearly impossible.
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