speed of light vs. "speed of gravity"

HarryKeogh · 13th March 2003, 06:25 AM

say the sun popped out of existence. we wouldnt know for around 7 minutes because of it's distance and how long the sun's light takes to reach us. ok, simple enough.

but if the sun popped out of existence would it's gravity exerted on us (and every other object in our solar system) cease immediately or does it travel at a certain speed?

CurtC · 13th March 2003, 06:31 AM

Most scientists think it travels at c. It's really really hard to measure though (suns don't normally just pop out of existence), so work is still being done. They're trying to detect gravity waves from things with changing gravity, such as two massive stars orbiting each other in a tight orbit.

garys_2k · 13th March 2003, 06:33 AM

Gravitationally caused distortions in space-time move at the speed of light. We'd stay on orbit until the sun's non-existence entered our reality, about seven minutes after it went away from the point of view of an observer located right near it. The sun is not just 93 million MILES from the earth, but it is actually displaced seven minutes from us, as well. Nothing about the sun, no "communication" from it, can get here faster than light.

scotth · 13th March 2003, 06:44 AM

Quote:

Originally posted by HarryKeogh
say the sun popped out of existence. we wouldnt know for around 7 minutes because of it's distance and how long the sun's light takes to reach us. ok, simple enough.

but if the sun popped out of existence would it's gravity exerted on us (and every other object in our solar system) cease immediately or does it travel at a certain speed?

This may be a bit out of date, but....

The speed of light and the speed of gravity should be identical. That is what current theory calls for.

My understanding of the current experimental evidence to support this:
1) Watching short period massive binary star systems over time indicate that they loose orbital energy at a rate that is consistent with the theory that they are producing gravity waves.
2) Numerically, the rate of energy loss is consistent with what is predicted if our current theory concerning gravity is correct.
3) Gravity waves have yet to be directly detected. (This may be out of date), but theory indicates detecting them would be a daunting task unless some fairly rare astronomical event occurs in our galactic neighborhood.
4) We are currently building better gravity wave detectors.

We will know alot more if/when we can directly detect gravity waves.

Some points to ponder about waves in general
1) In order to have a wave of any type, a field must be propagated at a finite speed.
2) Therefore, if gravity is propagated at infinite speed it would exclude the possibility of gravity waves.
3) Conversely, if/when gravity waves are detected, it conclusively rules out the possibility of infinite propagation speed.

Andonyx · 13th March 2003, 06:48 AM

You know they just did some major reserach on this a month ago:

http://www.arstechnica.com/archive/news/1042065116.html

There's one article.

And here's another:

http://physics.about.com/library/weekly/aa011503a.htm

Agammamon · 13th March 2003, 06:53 AM

Anyone who has seen Star Trek: Generations will have noticed that the mad scientists plan wouldn't have worked. Making the star nova would have had no effect on the path of the space thingy until the EM wavefront reached the location of the planet, frying it within a couple of seconds.

13th March 2003, 06:25 AM	#1
HarryKeogh Catholic School Survivor Join Date: Jan 2003 Location: New York, NY Posts: 11,342	speed of light vs. "speed of gravity" say the sun popped out of existence. we wouldnt know for around 7 minutes because of it's distance and how long the sun's light takes to reach us. ok, simple enough. but if the sun popped out of existence would it's gravity exerted on us (and every other object in our solar system) cease immediately or does it travel at a certain speed?

13th March 2003, 06:33 AM	#3
garys_2k Muse Join Date: Jan 2003 Posts: 756	Gravitationally caused distortions in space-time move at the speed of light. We'd stay on orbit until the sun's non-existence entered our reality, about seven minutes after it went away from the point of view of an observer located right near it. The sun is not just 93 million MILES from the earth, but it is actually displaced seven minutes from us, as well. Nothing about the sun, no "communication" from it, can get here faster than light.
garys_2k Muse Join Date: Jan 2003 Posts: 756	__________________ - Gary

13th March 2003, 06:44 AM	#4
scotth Atheist Political Candidate Join Date: Feb 2003 Location: DFW, TX area Posts: 1,801	Re: speed of light vs. "speed of gravity" Quote: Originally posted by HarryKeogh say the sun popped out of existence. we wouldnt know for around 7 minutes because of it's distance and how long the sun's light takes to reach us. ok, simple enough. but if the sun popped out of existence would it's gravity exerted on us (and every other object in our solar system) cease immediately or does it travel at a certain speed? This may be a bit out of date, but.... The speed of light and the speed of gravity should be identical. That is what current theory calls for. My understanding of the current experimental evidence to support this: 1) Watching short period massive binary star systems over time indicate that they loose orbital energy at a rate that is consistent with the theory that they are producing gravity waves. 2) Numerically, the rate of energy loss is consistent with what is predicted if our current theory concerning gravity is correct. 3) Gravity waves have yet to be directly detected. (This may be out of date), but theory indicates detecting them would be a daunting task unless some fairly rare astronomical event occurs in our galactic neighborhood. 4) We are currently building better gravity wave detectors. We will know alot more if/when we can directly detect gravity waves. Some points to ponder about waves in general 1) In order to have a wave of any type, a field must be propagated at a finite speed. 2) Therefore, if gravity is propagated at infinite speed it would exclude the possibility of gravity waves. 3) Conversely, if/when gravity waves are detected, it conclusively rules out the possibility of infinite propagation speed.

13th March 2003, 06:48 AM	#5
Andonyx Graduate Poster Join Date: Jul 2002 Posts: 1,834	You know they just did some major reserach on this a month ago: http://www.arstechnica.com/archive/news/1042065116.html There's one article. And here's another: http://physics.about.com/library/weekly/aa011503a.htm
Andonyx Graduate Poster Join Date: Jul 2002 Posts: 1,834	__________________ Andonyx www.andonyx.com Shy Gypsy Slyly Shyly Tryst By My Crypt.

13th March 2003, 06:53 AM	#6
Agammamon Graduate Poster Join Date: Jan 2003 Posts: 1,385	Anyone who has seen Star Trek: Generations will have noticed that the mad scientists plan wouldn't have worked. Making the star nova would have had no effect on the path of the space thingy until the EM wavefront reached the location of the planet, frying it within a couple of seconds.
	__________________ It will be a great day when the US Air Force has all the bombs it needs and the NEA has to hold a bake sale in order to pay its lobbyists.

13th March 2003, 06:31 AM	#2
CurtC Illuminator Join Date: Aug 2001 Location: Dallas, TX Posts: 4,758	Most scientists think it travels at c. It's really really hard to measure though (suns don't normally just pop out of existence), so work is still being done. They're trying to detect gravity waves from things with changing gravity, such as two massive stars orbiting each other in a tight orbit.