<< > If an ET civilization were to transmit an optical beacon, say, a
> coherent signal with no modulation. Should this signal pass through
> a large body's gravity field, what effect if any is imparted on the
> signal? Does phase change?
It would be deflected, possibly to the point of producing two images of
the source (this does happen for starlight). The deflected path would
be longer, so the phase would be delayed, but, unless you had some phase
reference that would be academic. There might be some extra general
relativity delays, but I'm not sufficiently familiar with the topic to
know whether these are just those corresponding to the deflection effect.>>
Nice answers Dave!
I published a couple of SETI articles on gravitational lenses and SETI a few
years back; one was in the 1987 SETI Conference proceedings. You indeed get a
phase lag between the signal-images and this causes interference effects.