Tom Van Flandern

Tom Van Flandern argues that the pre-general relativity formulation of gravity as a force of nature rather than as a pure geometric effect of curved space-time, is correct. He bases this claim on the observation that speed of gravity can't be appreciably less than the speed of light, since that could be detected by changes in the angular momentum of the planets. Instead he proposes a LeSage-like mechanism with super-luminal particles, travelling some 100 times the speed of light. He claims that while faster-than-light force propagation speeds do violate Einstein special relativity (SR), they are in accord with Lorentzian relativity, which has never been experimentally distinguished from special relativity.

Specifically Van Flandern notes that if gravity travels at the speed of light, as is assumed under general relativity (GR), then over time the paths of planets would shift to a degree that could easily be measured. In order to avoid this shift, or aberration, the speed of propagation must be faster, and given the length of time that we have been observing orbital motion, it must be at least 100 times as fast as the speed of light. The leap from this observation to requiring an entirely new theory, one essentially debunked a century ago, is left unexplained.

Only days after mentioning his claims on the internet, a critique was posted that stated that standard general relativity includes terms that make the observations match his lack of aberrations. Van Flandern claims that the lack of orbital drift can only be explained by a faster speed for the propagation of gravity, but in fact the very nature of general relativity is based on forces with a complex "direction", including force terms that exactly cancel out the effect Van Flandern claims proves GR to be wrong. Not only does it explain them, but it does so in a way that is completely "built in" to the theory, requiring no external framework. That is, GR not only explains the lack of aberrations, but does so in a completely "natural" way.

The scientific consensus considers Tom Van Flandern's theory to be crankishish, and that Van Flandern simply fails to understand the argument against his theory. To this day he has simply dismissed all such arguments and refused to address them directly. This consensus opinion should be contrasted with other non-standard gravitational theories such as Modified Newtonian Dynamics. Although the latter theory is considered wrong by most physicists, it is widely believed that proponents of the latter theory are at least "playing the game" in that they seriously responding to their critics, changing their theories to match criticisms, and that some of the disagreements with the standard model of gravity involve the results of observations which have not been made yet.

In 1970s Van Flandern was trying to find the 10th planet in our Solar system.

Tom Van Flandern's non-standard theory of gravity

A summary of the problem with Van Flandern's theory follows. Consider the Earth revolving around the Sun. It takes eight minutes for light to travel from the Sun to the Earth. Van Flandern asserts that if you simulate a gravitational system in which the force of gravity is pointed in the direction of where the objects were eight minutes ago, you end up with an unstable system, and asserts that in order to create a stable system the forces have to point in the direction of where the objects are at the current time.

Where Van Flandern disagrees with mainstream opinion is the assertion that that proves that gravity must propagate instantaneously. This is not the case. Most scientists believe that his mistake is to think of the forces being transmitted rather than the potentials.

Imagine the Sun being stationary, and the gravitational potentials moving away from the Sun at the speed of light. The potentials would be concentric circles. Now imagine the Sun starting to move. The lines of equal potentials will begin to bunch up in front of the Sun and start to expand behind the Sun. Now imagine the Earth in front of the Sun, and ask yourself what direction the force of gravity will be pointed at. The force of gravity will point down the slope of the potentials and will be pointed at where the Sun is at the moment, not where the Sun was in the past. However, causality is not violated. If the Sun suddenly shifted direction, there would be a delay before this change affects the forces and the potentials affect the Earth. (I wish I could draw some pictures.)

Note that the same thing happens with electromagnetic forces.

External links

Tom Van Flandern's argument [1]

Rebuttals at [1] and [1]

Usenet debate on news:sci.physics newsgroup archived at [1]

Tom Van Flandern's search for Planet X [1]