When Black Holes Collide

EricTheGreen writes "CNN.com reports on a pair of black holes in a mating dance that can only end badly for both of them. Fortunately they've still got several million years for the emotional rush to wear off and realize what a terrible mistake they're both making..."

Re:Sooner than you think

[BlewScreen]

I've always speculated as whether gravity travels like light. Would "gravity waves" from the merge be felt here on earth the instant it happened, or would it take the same amount of time as light/electromagnetic radiation to reach us?

If you take a look at this book [amazon.com], you'll find that there is a way to measure the "speed of gravity" (according to the author) and that it is indeed faster than the (current) speed of light.

I'm not going to agree or disagree with what he puts forth, but if you're interested in questions such as the one you propose above, you'll probably find the book interesting. The supposition is that the speed of light and the speed of gravity were, at the time of the big bang, equal, and that the speed of light has gradually slowed over time.

I think the answer the author would give to your question is that the "gravity waves" you mention would arrive before the light would, but it would not be instant.

-bs

Re:Why?

[mnemonic_]

Probably because you don't know how to punctuate quotations properly.

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Re:something I always wondered

[BinaryOpty]

There's a difference between the strength of a gravitational field and a gravitational gradient. It's like at the center of the Earth. The gravitational gradient there (relative to the Earth's field) is zero, but the force of all that overhanging rock is pretty high. You wouldn't float there comfortably with no force acting on you. You'd be squished.

Doesn't Newton's shell theory state that when within a large spherical body of mass you can treat the mass as a shell of radius to where you are within it because the mass that's further out than you ends up cancelling out? As such, if the center of the earth was somehow hollow and you somehow got transported there or something, then you would float because by the shell theory all of the mass above you is cancelling out all the mass below you and thus you have a net gravitational force of 0 pulling on you. The "overhanging" rock wouldn't squish you because you'd have "underhanging" rock to counteract its pull (even though those terms mean nothing if you're at the center of the planet where essentially every direction is up).