# Carlip's explanation of lack of gravitational aberration

by hkyriazi
Tags: aberration, carlip, explanation, gravitational, lack
 P: 1,441 Carlip's article is not dispositive of the issue nor was it intended to be - he makes the point that Van Flanderen's argument based upon the the apparent lack of aberration is not valid evidence for faster than c gravitational action - Feynman discusses the same problem in the context of electrostatic fields. I do not know if this is worth consideration - but the situation is somewhat analogous to what is observed with light from distant stars - we use the aberration angle to measure the earths motion relative to the light source - but it is not reciprocal - we cannot conclude anything about the relative motion of the light source from our measurment of the aberration angle- there are a number of radial photon paths eminating from the source - and if the source moves we are simply capturing a different ray to use when we measure the aberration due to the earths motion about the Sun - in the case of the gravitational effect of the Sun, the G field is radially divergent so as the earth moves from one position to another our motion is affected by a different element of the radial spoke (so to speak)... so the next position of the earth is influenced by a different radial angle. The effect is to appear as though the line of communication is instantaneous - this crude explanation works for the path of the earth if it were moving in a straight line - but there is almost no curvature to the earths motion in a very short time element - so the effect "almost" exactly corresponds to a situation where the force points in the direction of the present position rather than the retarded position of the earth.
 P: 8 As for gravitational radiation entering the equation in our solar system, the only bodies we have seen that emit this are massive binary pulsars, black holes, and extremely large bodies moving at extreme speeds, and last I looked we had no dual pulsars or other such in our solar system. http://en.wikipedia.org/wiki/Gravitational_wave http://math.ucr.edu/home/baez/physic...radiation.html All other gravitational radiation emitted from smaller bodies has already been shown to be virtually undetectable. So this may indeed apply to light passing binary pulsars, but no such explanation can be used for objects within our solar system.
Emeritus
P: 7,204

## Carlip's explanation of lack of gravitational aberration

Consider the following problem. Determine the "speed of electromagnetism" based on an analysis of the coulomb force law.

One of Carlips many points is that if you analyze this simple E&M problem, you'll find that the "speed of electromagnetism" is "infinite", using the same logic one used to determine that the "speed of gravity" is infinite. This suggests that said notion of "speed" is flawed, otherwise we'd be arguing that the "speed of light" is infinite, and we know that is not the case from multiple experiments.

The usual issue is that people have some pre-existing intuitive notion of how this sort of "speed" is determined, rather than thinking it through. This makes any discussion of the point hard, because one can't demonstrate the errors in a chain of logic where there is no chain of logic.

If one makes some incorrect assumptions, it's possible to formalize the argument a bit more as to why the direction of a force should indicate it's speed, which helps to see where the problem is.

These incorrect assumptions would be that the E&M force is carried by a particle (which is pretty close, but the actual correct assumption is that it's carried by VIRTUAL particles ), that these VIRTUAL particles have an actual "speed" which is equal to the "speed of light" and is in a radial direction (I don't know if this is correct or not, it's a suspect assumption), that the momentum of a particle must point in the same direction as its velocity, (definitely untrue for VIRTUAL particles - see http://math.ucr.edu/home/baez/physic...particles.html which illustrates how the momentum might even be in the opposite direciton of travel, which is required for attractive forces ), and that said virtual particle is absorbed by the receiving particle transferring its momentum (probably an OK assumption).

Given these incorrect assumptions, one can envision detecting the change in state of the motion of a test charge by observing the force on a stationary test charge some distance away. Unfortunately, these assumptions are still incorrect.

One of the points of Carlips paper is that if you actually analyze Maxwell's equations to get the E&M field of a moving charge, this simple scheme for measuring "speed of propagation" doesn't actually work. To see this requires that one have the mathematical / physical background to actually work with Maxwell's equations - div, grad, curl and all that. Sorry, but sometimes one DOES have to actually sit down and study the math to get good physics!

One will find discussion of this issue in E&M textbooks as well as in Carlips paper - it's usually talked about as the Coulomb gauge vs the Lorentz gauge - but typically said discussion is even more technical than Carlip's paper.
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