# on the question of "What is the speed of gravity?" **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [May 9, 2003, 4:18pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136 "2003-05-09T16:18:18Z")\ **Posts on this page:** 11\ **Page:** 3
**Author:** ![dkoik](https://avatars.discourse-cdn.com/v4/letter/d/e36b37/32.png) [@dkoik](https://boards.straightdope.com/u/dkoik)\ **Post date:** [May 16, 2003, 4:16am UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/41 "2003-05-16T04:16:33Z")
Regarding instantaneous action and its usefulness to transmit information, Slate currently has posted a discussion regarding the principle as applied to quantum computing and quantum cryptography. [http://slate.msn.com/id/2082874/entry/2082873/](http://slate.msn.com/id/2082874/entry/2082873/) ---
**Author:** ![UselessGit](https://avatars.discourse-cdn.com/v4/letter/u/74df32/32.png) [@UselessGit](https://boards.straightdope.com/u/UselessGit)\ **Post date:** [May 16, 2003, 5:32pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/42 "2003-05-16T17:32:22Z")
Doesn´t monarchy travel faster than the speed of light, though? My experiments with what I call “monarchons” have gone off to a slow start, so let me know if you hear about a king with slack security… ---
**Author:** ![danceswithroaches](https://avatars.discourse-cdn.com/v4/letter/d/8797f3/32.png) [@danceswithroaches](https://boards.straightdope.com/u/danceswithroaches)\ **Post date:** [May 28, 2003, 7:28am UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/43 "2003-05-28T07:28:02Z")
In the 8 minutes it takes for light to travel from sun to earth, the earth moves about 19 arc-seconds through its orbit. Because of this small angle the pressure of the light exerts a small force against the direction of orbital motion. If gravity had a similar lag it would exert an attractive force in the same direction. This force is large enough that the orbital radius would double in about 1200 years. No such effect is observed, so there is no such force. Specially trained smart people have calculated that the speed of gravity has to be at least 10^8 times the speed of light. Here is the complete explanation: [http://www.metaresearch.org/cosmology/speed\_of\_gravity.asp](http://www.metaresearch.org/cosmology/speed_of_gravity.asp) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 28, 2003, 9:57pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/44 "2003-05-28T21:57:22Z")
> [@](#): > > Yeah, but the advantage of this method over EPR type effects is that most important phrase “So far as we know…”. Yes, and I put that phrase in there for a reason. I am **not** prepared to state that FTL communication is impossible. I am prepared to say that if FTL communication is possible, then it would lead to some other really weird effects, but I’m likewise not prepared to state that those weird effects are impossible, either. **danceswithroaches** , the effect you mention is the Newtonian orbit-decay problem mentioned by **Punoqllads**. The problem does not come up in General Relativity: In GR, the speed required of gravity (both by theory and experiment) is exactly c. I don’t have time to fully dissect the link you posted, but I’ll start by pointing out that it’s not published in any peer-reviewed journal, which means that it’s no more reliable a source than any other web page. With a little searching, you can probably find web pages which “explain” gravity as being the result of the great turtle the Earth is riding on inhaling and sucking us all down. But that doesn’t make it true. ---
**Author:** ![buckminster](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@buckminster](https://boards.straightdope.com/u/buckminster)\ **Post date:** [May 29, 2003, 3:01am UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/45 "2003-05-29T03:01:49Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*Yes, and I put that phrase in there for a reason. I am **not** prepared to state that FTL communication is impossible. I am prepared to say that if FTL communication is possible, then it would lead to some other really weird effects, but I’m likewise not prepared to state that those weird effects are impossible, either. > \*\* Hey Chronos, Are you are just trying to hedge your bet because if FTL anything were possible, we would have to give up some long cherished principles. Ya know, minor stuff, like causality… Come on, even a post modern deconstructionist astrologer would have to think twice before they are will to kiss that puppy off. But I agree with your position. One of the things that separates science from other human activities is that we gotta accept that there is some finite probability that FTL could exist. I’ve been reading postings about gravity, cosmology and related topics on [Belief.net](http://Belief.net) and that willingness to say ‘maybe’ is the most fundamental difference. best regards, buck * * * “It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring.” - Carl Sagan ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [May 29, 2003, 4:44am UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/46 "2003-05-29T04:44:19Z")
Note that the link provided by **danceswithroaches** is to an essay by Tom Van Flandern. It is most definitely not mainstream science. I don’t have the knowledge and training to dissect the article, but FYI, anyone taking this as a statement of the position of cosmologists in general would be mistaken. Just so you know what you’re getting into. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [May 29, 2003, 1:26pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/47 "2003-05-29T13:26:45Z")
I found the Flandern essay interesting myself, but I’m not at all competent to critique it. Other people are and have found it, or at least the peer-reviewed paper on the subject he had published into a physics journal, totally wanting. [Re: Flandern article in Physics Letters A](http://www.lns.cornell.edu/spr/1999-09/msg0017879.html) by Chris Hillman: > [@](#): > > I think it is clear that each of these posts criticize different claims made by Flandern in the PLA paper, and each of them dismisses these claims as erroneous or even vacuous. Larry Mead even states the obvious: the referees simply goofed, and let an erroneous paper slip into print. It happens. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 29, 2003, 3:31pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/48 "2003-05-29T15:31:53Z")
> [@](#): > > Come on, even a post modern deconstructionist astrologer would have to think twice before they are will to kiss that puppy off. As it happens, I am not a post modern deconstructionist astrologer ;). But seriously, discarding causality is one of those Really Weird side effects I mentioned. I’m a little more willing than most to reject causality (but still not without some good evidence!), although I admit that that may be partially wishful thinking. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [May 29, 2003, 5:10pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/49 "2003-05-29T17:10:17Z")
> [@](#): > > \*Originally posted by danceswithroaches \* > \*\*In the 8 minutes it takes for light to travel from sun to earth, the earth moves about 19 arc-seconds through its orbit. Because of this small angle the pressure of the light exerts a small force against the direction of orbital motion. If gravity had a similar lag it would exert an attractive force in the same direction. This force is large enough that the orbital radius would double in about 1200 years. No such effect is observed, so there is no such force. Specially trained smart people have calculated that the speed of gravity has to be at least 10^8 times the speed of light. \*\* Now wait a minute. Are you telling me that the effect of the sun’s mass on the fabric of space resets to zero unless there is an actual mass there to interact with? The warping of space by the sun is present regardless of the presence of the earth. The warping changes slightly as the two gravity wells move through each other but I fail to see why you would need to worry about this. What did I miss? ---
**Author:** ![buckminster](https://avatars.discourse-cdn.com/v4/letter/b/13edae/32.png) [@buckminster](https://boards.straightdope.com/u/buckminster)\ **Post date:** [May 30, 2003, 5:06am UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/50 "2003-05-30T05:06:30Z")
> [@](#): > > \*Originally posted by Exapno Mapcase \* > \*\*I think it is clear that each of these posts criticize different claims made by Flandern in the PLA paper, and each of them dismisses these claims as erroneous or even vacuous. Larry Mead even states the obvious: the referees simply goofed, and let an erroneous paper slip into print. It happens. > \*\* One of the unusual aspects to this line of research has been the inclusive manner that the ‘fringe’ element has been treated by the mainstream researchers. This is a good thing. Yeah, Flandern has some strange opinions. And the first generation of scientist who tackled gravity wave detection are no longer in the loop any more either. Overall, society and science is better served by giving these fellows an opportunity to be heard and participate. I seriously doubt that Flandern’s theories have any validity. but if scientist don’t address these unusual viewpoints, then these fringe elements seem to get a big boost from the conspiracy, UFO, ancient astronaut, ESP, pyramids built by aliens folks. I wonder if astronomers had addressed the[theories of Velikovsky](http://skepdic.com/velikov.html) 50 years ago, would anyone would bother to attend an event such as this [symposium](http://www.knowledge.co.uk/sis/50years.htm). Maybe I’m being optimistic (a serious fault of mine) but I like to think that most people are reasonable and they would start to catch on to these guys after awhile. best regards, buck * * * “If we don’t believe in freedom of expression for people we despise, we don’t believe in it at all.”- Noam Chomsky ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 30, 2003, 8:57pm UTC](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136/51 "2003-05-30T20:57:25Z")
On the one hand, there is value in letting the fringe elements have their say, but on the other hand, you can’t address all of the fringes. The problem is that there are far too many of them. If professional physicists and astronomers (and I assume this is true of other scientists as well) addressed every “theory” which crossed their desks, then they wouldn’t have time to do anything else at all. One has to draw a line somewhere, but unfortunately nobody seems to agree on where. The presentation of an idea also makes a big difference. If a person writes a paper saying that “Assuming a Newtonian model of gravity, analysis of motions in the Solar System indicates a speed of gravity of at least 10[sup]9[/sup]c”, then at worst the paper will be regarded as interesting but irrelevant. If nothing else, such a paper can be used as evidence against a Newtonian model. If, though, the person writes a paper saying “Our analysis of Solar System motions proves that gravity must have a speed of at least 10[sup]9[/sup]c”, then it’s hard to say that the paper is anything other than just plain wrong. [Previous page](https://boards.straightdope.com/t/on-the-question-of-what-is-the-speed-of-gravity/174136.md?page=2)