alt.sci.physics

LIGO and null results

Can someone please explain why LIGO and similar interferometric
gravitational wave detectors should be expected to find anything other than
the null results so far found?

It seems to me that the effect of a passing gravitational wave, a transient
variation in gravitational potential, would be analogous to raising or
lowering the height of the whole interferometer in the Earth's field, an
action for which General Relativity appears to predict a null effect. In
that theory, it has long been predicted that both distances and the speed of
light are modified by the same factor under a change of gravitational
potential, so that the round trip time for to- and fro- laser beams would be
unchanged even though the passing wave affected the distances along the
interferometer arms. Light travels slower in a region of lower potential by
the same factor as lengths are reduced, and vice versa.

The horrible suspicion is that these experiments are suffering from the
inverse of the misconception that we now know invalidated the
Michelson-Morley experiment in its aim of detecting a preferred frame for
light propagation - the idea that only light and not the forces maintaining
the arm-lengths would be affected by motion in the ether. (We now know the
latter are electromagnetic, and thus would be affected in the same way as
light in a preferred frame, if it existed, leading to a null result and if
anything supporting the case for a Lorentzian ether model!).

In the LIGO case, it seems (in what I have read so far) to be assumed
implicitly that the light propagation from the lasers is independent of
changes in gravitational potential, which are assumed to affect only the
arm-lengths.

I hope someone can point me to an analysis of the LIGO-type experiments
which shows how the effects of gravitational changes on both light
propagation and lengths are explicitly taken into account, and why the
effects do not cancel as GR seems to predict.

Trevor Morris