Explanation of Paradox

DaveL,

Others have made similar arguments, also hoping to avoid the observation-based conclusion that gravitational force appears to propagate much faster than light. Search the USENET archives for: Carlip Van Flandern non central force.

I believe that some of the articles on tvf's <i>Gravity</i> CD also touch on this.

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TVF points out two problems with this approach:

A) Even though the math works, there are no known phyical phenomena to justify adding these terms to our models. (We're still looking, of course. Absense of evidence is not evidence of absense. But ...)

If there were such phenomena they ought to cancel *all* non central forces (for example tidal forces), not just the ones (for example the aberration that would be induced by light speed propagation of a force) that don't support a particular theory.

Regards,
LB

Why would the speed of gravity have an effect on the orbit of a planet? I'm kind of stupid about this stuff but it seems to me the gravity field would be there for the planet even if gravity was not moving at all. And why would gravity travel anyway?

Thanks for the response, Larry Burford.

I am looking at this: www.lunchwithgeorge.com/lwg_gravity.html

Towards the bottom is very interesting, Carlip's claim that EM forces derived from retarded potentials will point to an extrapolated position rather than the 'instantaneous' position. I'll have to look into that. If that's true, there is no need to postulate either advanced forces or instantaneous ones, at least to the problem of the earth staying in orbit.

I've not found any explicit mention of considering time-advanced forces but I am still reading.

Anyhow, if what Carlip says about retarded EM (Leinard-Weichert) potentials is true, I am going to lose interest in the whole thing, probably, because the credibility of the whole problem will go out the window for me, unless one of the TVF/MR papers has an explicit working out of the force directions under GR, rather than just a diagram, that can show that GR is different than standard EM theroy in this area. I am inclined to take Carlip's word that GR will be the same as EM here, unless somebody with an interest has demonstrated otherwise.

To me it does seem more plausible to have time-advanced forces than instantaneous ones, but any of our feelings about it are irrelevant. All that matters is what works to explain observations.


Its not obvious to me that advanced forces would cancel tidal forces. Is that worked out someplace?


Jim, what I am referring to is described here

www.metaresearch.org/cosmology/speed_of_gravity.asp

<blockquote id="quote"><font size="2" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by DaveL</i>
<br />... unless one of the TVF/MR papers has an explicit working out of the force directions under GR, rather than just a diagram, that can show that GR is different than standard EM theory in this area. I am inclined to take Carlip's word that GR will be the same as EM here, unless somebody with an interest has demonstrated otherwise.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">Figure 3 is an aid to understanding the derivation that follows, which shows that a linear extrapolation is grossly insufficient in the case of gravity. Carlip does not dispute that point, and in fact relies on it in his PLA paper. That is in part what led to my second "speed of gravity" paper, which mentions the Sherwin-Rawcliffe experiment. That experiment (which no one ever bothered to replicate, probably because it would be a career-killer to do so) showed that a linear extrapolation is insufficient even for E&M. -|Tom|-

It did occur to me that linear extrapolation will not fully restore angular momentum conservation, by itself. But it would increase the amount of time required to note an effect. Has anybody calculated how long in that case to have an effect on the earth? You have 1200 years to double the radius if the force points to the past position. That's a very fast-acting effect, in terms of cosmic time. So if linear extrapolation meant it took a thousand or a million times longer to see an effect, it would still be readily apparent.

Anyhow I am not giving Carlip's argument its full due, I suspect. There is more to it than just the fact (according to him) that retarded potentials lead to a linear extrapolated effect, I think. Its going to take me longer than tonight though to get a handle on it. Also he mentions a paper by Damour where I gather this is addressed further.

Here is a link to Feynman's Nobel Lecture in which he talks about the application of advanced-action to the problem of radiation resistance:

nobelprize.org/physics/laureates/1965/feynman-lecture.html

There is a paper with Wheeler too, but don't have a link at the moment.

Here is a link to Huw Price's website:

www.usyd.edu.au/time/price/TAAP.html