In sci.astro Tom Roberts wrote:
wrote:
3 Deviation of stars light by Sun is optical
[...]
And, of course, if you insist on it being optical effects, you must TUNE
the "effects" you claim to be almost precisely the values predicted by
GR -- unless you have an independent method of computing the index of
refraction(etc.), you have no leg to stand on; your paper gives no such
independent computation.
More than that -- he would have to explain why the observed dependence of
the deflection on the angle from the Sun ("solar elongation angle" of the
source whose light is being measured) agrees with the predictions of GR.
The usual introductory textbook derivation of deflection of light by the
Sun usually computes the deflection for a beam just grazing the Sun's
surface, for which the deflection is largest. But light passing quite
far from the Sun is still deflected; the deflection is smaller, but still
easily measurable by VLBI for radio sources even more than 90 degrees from
the Sun.
Shapiro et al. have a nice paper (Phys. Rev. Lett. 92 (2004) 121101) in
which they look at over a million measurements, with 541 radio sources and
87 VLBI sites. This is enough data that they can successively drop out
sources with lines of sight within 10 degrees of the Sun, 20 degrees,
30 degrees, on up to 90 degrees. The error bars get bigger -- both because
the deflection is smaller and because there are fewer measurements -- but
there is no sign of any deviation from the GR prediction. Even restricting
to sources at lines of sight at least 40 degrees from the Sun, the errors
are only about 2%.
If one wants to explain this as being due to the Sun's atmosphere, one must
claim not only that the atmosphere extends *far* beyond the Sun (picture a
light ray passing 40 degrees from the Sun...), but also that the density of
this enormous, previously unnoticed "atmosphere" just happens to vary in
exactly the right way to precisely reproduce the predictions of GR.
Steve Carlip