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    Re: gravitational fields
    From: Frank Reed
    Date: 2008 Mar 16, 00:10 -0400

    Bill writes:
    "Off topic, but allow me put it another way--an old question.  Our Sun is
    gone in a nanosecond. Light continues to come our way for approx. 8 minutes.
    What happens to gravity (Sun's) the moment it ceases to exist?(Not a star
    size; red yadda yadda vs. ... trick question)."
    Ok, I can't resist . General relativity, the best model of gravitation
    that we have, is incapable of answering this particular hypothetical
    question. Why? Because the setup violates mass-energy conservation, and this
    is explicitly required by GR. But you can do similar problems, and of
    course, when you do, the theory says that changes in the gravitational field
    propagate at the speed of light. There's no theoretical reason to believe
    otherwise, and there is also some observational evidence that confirms this
    specific feature of the model. Again, I would be happy to chat more about
    this, but I worry about annoying people with off-topic material, so again,
    if you want more, join me at Compuserve SciMath (see previous post for the
    Navigation List archive: www.fer3.com/arc
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