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Would the Earth Have A Delay Reaction if the Sun disappeared

  1. Jun 13, 2015 #1
    So, I heard the other day from someone online who claimed that if the sun would to suddenly disappear that the Earth would still travel in its regular path for 8 minutes before breaking off.

    The person claimed that because it takes light 8 minutes to reach Earth, and that since nothing can travel faster than the speed of light that it would take the information that "the sun was gone" 8 minutes to reach the Earth thus the Earth wouldn't react until 8 minutes later.

    Is this accurate? And if so, can someone explain to me how?

    Thank you very much.
  2. jcsd
  3. Jun 13, 2015 #2
    That is indeed correct.
    What part do you have trouble understanding? As you said yourself, nothing can travel faster than light, and that of course includes gravity. So, the change in gravitational force would take 8 minutes to reach us. Up to that time we'd still be receiving "old information", so to speak.
  4. Jun 13, 2015 #3


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    This is a frequent question on PF.
    Unfortunately, there is not a straightforward answer to it. For a start, you cannot envisage taking away the Sun, 'just like that!'. If you 'nuked the Sun, its centre of mass would not change so the gravitational field at Earth would not change. Of course, after 8 minutes, there would be an almighty flash, arriving on Earth!
    If you 'nudged' the Sun with a large, high speed object, it would be the position of the centre of mass of the Sun plus Object that would affect the Field at Earth. This wouldn't be a 'sudden' event, at all.
    Neverthless, any effect at earth would still be delayed.

    However, if you want a thought experiment that would be more feasible. If we had a binary pair of stars at the centre of our orbit, the varying gravitational potential as the stars moved from end on to broadside on, in their mutual orbits - and back again would be 8 minutes delayed and would give the Earth a wobble in its orbit that lagged about 8 minutes behind the relative positions of the two stars.
  5. Jun 13, 2015 #4
    This is something that is more easily explained in terms of General Relativity. In Newtonian mechanics, the gravitational force change is transmitted instantly from one location in space to another. However, this is not the reality of the situation. In reality, it is the curvature of space-time, induced by the presence of a massive body (in this case, the sun), that is responsible for the gravitational effect. If the massive body somehow vanished, the curvature of space-time would have to readjust, but the readjustment effect would not take place instantaneously. It would travel outward at the speed of light from the place where the massive body had been.

  6. Jun 13, 2015 #5
    What's the experimental confirmation of gravity traveling at the speed of light actually? We've never seen gravity waves after all.
    Or is it more implicit confirmation since the GR formulas all involve c somewhere or another, and something like Mercury's precession validated gravity's speed alongside with it?
  7. Jun 13, 2015 #6
    I'm not sufficiently knowledgeable about general relativity to answer this. Hopefully some of our relativity mavens will jump in and help.

  8. Jun 14, 2015 #7


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