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Would the removal of the sun result in a shockwave?

  1. Feb 3, 2009 #1
    Hello everyone, good day,
    So I understand that gravity travels at the speed of light and such. So naturally, if the Sun were suddenly gone, it'd take ~8 minutes for us to fly off and die. But I was reading Michio Kaku's "Parallel Worlds" and he used the trampoline/bowling ball analogy for gravity and then used the finite speed of waves in a sheet of fabric to say "gravity travels in similar ways". And that got me thinking: if the Sun suddenly disappeared, would the trampoline snap back (and even up), tossing the marble up? Taking the 2d analogy to the 3d, this would mean a sudden jump in time? Yea, I was just thinking of the specifics of the sun disappearing and thought I'd ask you guys to clarify for me.
    Thanks.
    -DT
     
  2. jcsd
  3. Feb 3, 2009 #2

    DaveC426913

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    One of the problems with this is that there is no way for the sun to suddenly disappear. Even if it exploded, the mass would fly off at sublight speeds, and the gravity from that mass would change at a leisurely pace.
     
  4. Feb 3, 2009 #3
    See
    http://en.wikipedia.org/wiki/Gravitational_Wave#Effects_of_a_passing_gravitational_wave

    for a visualization of passing gravitational waves.

    Since gravitational potential would change from earth and sun combined to earth alone, yes time and space would change as well...

    You can get an idea of the power radiated by the combined system, only roughly 313 watts, at

    http://en.wikipedia.org/wiki/Gravitational_Wave#Power_radiated_by_the_Earth-Sun_system

    ..in other words gravitational waves are normally quite difficult to detect...

    Maybe somebody will post a few calculations: my gut tells me the earth would begin moving without warp drive like acceleration....And if the sun exploded, rather than being quietly "removed", of course we'd be instantly annihilated in a burst of radiation as the gravitational wave reached earth .
     
  5. Feb 3, 2009 #4
    Conservation of energy-momentum in GR forbids the possibility of the Sun "suddenly disappearing" and the situation you describe.
     
  6. Feb 3, 2009 #5

    Fredrik

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    Just to clarify a little bit: The reason why we aren't really willing to answer the original question isn't that we're unwilling to consider situations that are "too extreme". We don't mind considering e.g. a spaceship that goes at 0.9999999999999c in one direction and a nanosecond later goes at 0.9999999999999c in the opposite direction, even though it would smash the ship into a quark-gluon plasma or something. In that case we can at least describe the curve that represents that (absurdly ridiculous) motion. But in the case of the Sun "suddenly disappearing", the problem is that there's no solution of Einstein's equation that describes a scenario like that. So the theory doesn't really say anything about it. We can't even ask the question properly in the framework of GR.
     
  7. Feb 3, 2009 #6
    Yea, I suppose so. I've asked a question or two on these forums (often of the form "a spaceship traveling 0.99999c") and never realized how realistic my questions were. I can't really think of a way to restate the question while still getting at the concept, so I declare close-dom.
     
  8. Feb 3, 2009 #7

    DaveC426913

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    I think the closest you might get is rapid orbiting pulsar binary. I believe this is what they're trying to detect gravity waves from.

    The point is, your question should still be valid within known physics if we contrive it right.
     
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