View Full Version here: : gravity / velocity
25-12-2010, 08:38 PM
Hi all, as it has been a long time between observing nights I have had way to much time to ponder.
I am not even sure that this question makes sense but here goes;
does gravity have speed / velocity :question:
The effects of gravity travel at the velocity of the speed of light in a vacuum (3x10^8 m/s).
Leveraging off of what Steven said in a another post regarding a query I had regarding black holes - gravity is an effect caused by curvature in space. Nothing can travel through that space faster than the speed of light and this includes any changes to its curvature due to any moving masses embedded in it.
I hope that Steven - or others - will correct me If I'm off-track.
26-12-2010, 07:55 AM
Oh boy .. simple question for mainstreamers but a can of worms for the 'non-conformists' !!
Einstein answered this question as part of the early stages of his General Relativity work, I think.
Special Relativity is really only meant to cover matter moving through space (as Mark has said).
But spacetime is not matter.
This subject is a topical one, given the impending Gravitational Wave detectors about to be launched into space.
An interesting question. My "biologist's"point of view (ie: I have a mere passing knowledge of subjects like GR and SR) is that gravity should propagate at the speed of light. But wouldn't that be interesting if gravity's effects were instantaneous at any distance? I wonder how that would change the way things work. Or if!
Man we've got some cool experiments happening over the next period of years, gravity wave detectors, SKA, LHC, planet hunting Kepler and many more. I can't wait to see how these things advance our understanding of the Universe.
Enjoy reading your Christmas present. I received "Death from the Skies" by Phil Plait and The Grand Design by a Mr Hawking. Also "One Small Step" on the history of space exploration.
26-12-2010, 10:44 AM
Gravity transients would propagate at the speed of light.
If Sun, by some miracle, were disappeared, we would notice this after 8 minutes. Or, if somewhere in space two black holes merge.. the effect would come to us after some time, propagating at speed of light.
However, the gravity field is associated with mass, no matter how distant it is - it behaves as if it is part of that mass and the effect is immediate - that means, as the mass is moving, so is it's gravity field.
The main proof that things are like this is if the Sun's gravity were "dragging" behind (with the speed of light), the planet's orbits wouldn't be stable.. But they are. Ergo, the Sun's gravity field is part of the Sun and it moves as one with the Sun.
This topic was discussed previously in this forum..
27-12-2010, 07:53 AM
I missed your inputs on our recent "Trillions of Earths" thread !
We were really getting into biological stuff there .. 'twould've been great to have your comments !! :)
Oh well ..
Yep there are heaps of interesting things going to come up in the New Year.
Looks like we're going to get some more info about the impact site on comet Tempel 1 as well ! I'm looking forward to that one also !
Got another book also .. Lisa Randall's "Warped Passages". Should be a good read .. if I can ever get out of Hofstadter's book, that is !
Cheers & Happy New Year, Stuart !! :)
Will post some thoughts re biology on the Trillions of Earths thread for your consideration. :)
27-12-2010, 12:03 PM
Are people over thinking this? Gravity is a measure of a force. The force is induced by Mass. As a force it has acceleration and velocity components relative to starting point, time, mass, friction and any other forces acting on the components inducing gravity.
27-12-2010, 03:13 PM
Hmm .. a very Newtonian view !
27-12-2010, 10:52 PM
So relativity doesn't consider gravity as a force (albeit a 'well' in space time). Isn't it still something acting on something else? (note that I probably do not correctly understand the concept of relativity - general or special)
28-12-2010, 09:17 AM
I think the original question was: "does gravity have speed / velocity ?"
The way I originally pictured this question was from a propagation-of-gravity-disturbances perspective.
The Newtonian view is cool - no probs ! It made me recheck the original question.
The question of "what is (ie: causes) gravity?" would seem to be a different question altogether, and ends up being highly speculative.
No one has entirely answered this one !
I think we need Brian W to chirp in … and add some meat to his original question …
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