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#1
08-25-2005, 12:08 PM
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The speed of gravity
I've been wondering - how fast do gravity waves travel?
By that, I mean, if the sun were to vanish somehow instantaneously, it would take us 9 minutes or so to actually notice, since the light waves take 9 minutes to reach us. But what would the gravitational effect be? Would it take the earth 9 minutes to "break orbit", or would we break free the second the sun vanished? Ringo 
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#2
08-25-2005, 12:21 PM
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Re: The speed of gravity
If gravity is really the curvature of the space-time continuum, then it seems reasonable to think that if the sun suddenly vanished it would take a while for the curvature to uncurve.
PairTheBoard
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#3
08-25-2005, 12:29 PM
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Re: The speed of gravity
[ QUOTE ]
I've been wondering - how fast do gravity waves travel? By that, I mean, if the sun were to vanish somehow instantaneously, it would take us 9 minutes or so to actually notice, since the light waves take 9 minutes to reach us. But what would the gravitational effect be? Would it take the earth 9 minutes to "break orbit", or would we break free the second the sun vanished? Ringo [/ QUOTE ] Gravity waves travel at the speed of light, they are similar to photons (they are quatized) If the Sun dissapeared right now, it would be impossible for us to tell until ~ 9 minutes after, we would still be in orbit in the meantime
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#4
08-25-2005, 12:38 PM
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Re: The speed of gravity
[ QUOTE ]
By that, I mean, if the sun were to vanish somehow instantaneously, it would take us 9 minutes or so to actually notice, since the light waves take 9 minutes to reach us. But what would the gravitational effect be? Would it take the earth 9 minutes to "break orbit", or would we break free the second the sun vanished? [/ QUOTE ] Newton's theory would have the Earth instantly break orbit. Einstein theorized that the gravity is not a force that travels instantaneously, but at exactly the speed of light. That is if the sun instantly ceased to exist, the change in the curvature of the spacetime fabric would reach us the exact moment after the sun's last breath of light. GoT
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#5
08-25-2005, 01:25 PM
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Re: The speed of gravity
I thought the whole curved space theory was created in order to solve inconsistencies in the Newtonian junx like simultaneity. The “Spooky” in “spooky action at a distance” included the fact that gravity seemed to affect things instantaneously, which just doesn’t fly. So…if the Sun “disappeared” instantaneously (which is fortunately impossible) wouldn’t space have to also change immediately? Make a computer model of the solar system and delete the sun. It should take that long.
Or am I wrong? It’s been known to happen… Edit: I definitely am missing something RE: gravity quanta/waves. I'm going to the googlibrary, tho...I'll be back...
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#6
08-25-2005, 01:39 PM
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Re: The speed of gravity
[ QUOTE ]
HotPants -- Gravity waves travel at the speed of light, they are similar to photons (they are quatized) [/ QUOTE ] I thought gravity waves were still theoretical. Something we have yet to find physical evidence for. In fact, I thought it was one of the missing links for a unified theory. PairTheBoard
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#7
08-25-2005, 01:46 PM
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Re: The speed of gravity
[ QUOTE ]
[ QUOTE ] HotPants -- Gravity waves travel at the speed of light, they are similar to photons (they are quatized) [/ QUOTE ] I thought gravity waves were still theoretical. Something we have yet to find physical evidence for. In fact, I thought it was one of the missing links for a unified theory. PairTheBoard [/ QUOTE ] Well, no, we haven't observed them directly. But the only theories that explain the orbits of observed pairs of massive objects orbiting each other (black holes and neutron stars) are the theories that have gravitons in them. My friend just when off to do a phd, trying to detect gravity waves with some people, I'll let you know if he sees any (I don't think he will) And as for the unified theory, this is beyond my limited knowledge, but yeah I think the unified theory predicts gravitons will have spin of 2, so if we observere gravitons with a spin of 2 (not just observe gravitons, since relativity predicts them) then yes this would be some good evidence for the unified theory
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#8
08-25-2005, 01:55 PM
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Re: The speed of gravity
[ QUOTE ]
[ QUOTE ] [ QUOTE ] HotPants -- Gravity waves travel at the speed of light, they are similar to photons (they are quatized) [/ QUOTE ] I thought gravity waves were still theoretical. Something we have yet to find physical evidence for. In fact, I thought it was one of the missing links for a unified theory. PairTheBoard [/ QUOTE ] Well, no, we haven't observed them directly. But the only theories that explain the orbits of observed pairs of massive objects orbiting each other (black holes and neutron stars) are the theories that have gravitons in them. [/ QUOTE ] The point is no one's saying those theories are very strong. They're just some good ideas that sound right. In the next 50 years we could easily come up with and provide evidence that supports an entirely different theory.
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#9
08-25-2005, 02:14 PM
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Re: The speed of gravity
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] HotPants -- Gravity waves travel at the speed of light, they are similar to photons (they are quatized) [/ QUOTE ] I thought gravity waves were still theoretical. Something we have yet to find physical evidence for. In fact, I thought it was one of the missing links for a unified theory. PairTheBoard [/ QUOTE ] Well, no, we haven't observed them directly. But the only theories that explain the orbits of observed pairs of massive objects orbiting each other (black holes and neutron stars) are the theories that have gravitons in them. [/ QUOTE ] The point is no one's saying those theories are very strong. They're just some good ideas that sound right. In the next 50 years we could easily come up with and provide evidence that supports an entirely different theory. [/ QUOTE ] Maybe, but I think that different theory will still have gravitons in there some where Or at least photons, It would seem impossible for a theory to be correct if it didn't account for light some how
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#10
08-25-2005, 02:43 PM
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Re: The speed of gravity
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] HotPants -- Gravity waves travel at the speed of light, they are similar to photons (they are quatized) [/ QUOTE ] I thought gravity waves were still theoretical. Something we have yet to find physical evidence for. In fact, I thought it was one of the missing links for a unified theory. PairTheBoard [/ QUOTE ] Well, no, we haven't observed them directly. But the only theories that explain the orbits of observed pairs of massive objects orbiting each other (black holes and neutron stars) are the theories that have gravitons in them. [/ QUOTE ] The point is no one's saying those theories are very strong. They're just some good ideas that sound right. In the next 50 years we could easily come up with and provide evidence that supports an entirely different theory. [/ QUOTE ] I don't think the strength of the observational evidence for General Relativity is properly stated. I used to work in Numerical Relativity, and GR expansions to several orders accurately predict the change in period of observed binary neutron stars over many orbits which is fairly strong evidence for gravity waves although indirect. Further, there have been many competing theories to GR and none have ever performed better concerning comparison to observational data at any astronomical scale (Solar system, Galactic, super-Galactic, etc.). There is not a single astronomical observation that has ever been suggested to be possibly in disagreement with GR. Beside QED, GR is the most successful physical theory in the history of mankind. It still may be wrong, but it isn't far wrong. GR is a very well tested and strong theory and certainly is not just some idea that sounds right.
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