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Speed of gravity - Interesting question

  1. Mar 5, 2007 #1
    Greetings, I learnt that the speed of gravity is the speed of light as einstein predicted that once the sun disappears, the earth would not instantaneously fly out of its orbit but only after an approximate 8 mins then the earth would spin out of its gravitational field tangent to the circle as it takes approximately 8 minutes for light from the sun to reach earth.

    Ok imagine yourself on ground level on earth. Both of ur palms are together with a piece of paper in between. Logic tells us that the paper falls when both palms are seperate. My question is:

    Since gravity travels at the speed of light, if we can complete a single " oscilation of ' clapping ' before the gravity from the centre of the earth reaches the paper, would the paper even move (fall)? Though i know that nothing can travel faster than the speed of light..
  2. jcsd
  3. Mar 5, 2007 #2
    before you start, gravity from the center of the earth has already reached the paper... goodnight un'
  4. Mar 5, 2007 #3
    Yes, there's that. It also wouldn't work because the gravity from the earth has already reached you. If you're talking about general relativity, the space around you is already curved according to the shape of the earth, and this will give the instantaneous appearance of a gravitational force. If you're talking about quantum physics, then gravitons that left the earth earlier have already reached you, and so there's no time delay in feeling the gravitational force.

    The time delay predicted by the finite speed of gravity will only allow you to detect changes in the local gravitational field.
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