Phillip Helbig---remove CLOTHES to reply wrote:

http://www.arxiv.org/abs/astro-ph/0306434

Here, the main point is that microlensing can't be the main source of
QSO variability. However, IF most of the dark matter is in compact
objects, then one WOULD expect to detect it (quantitatively; of course
microlensing has been observed, the question is how much mass is in the
objects and how is it distributed). Things might conspire so that the
signal is swamped by other variability, but if it is "just so" then one
should be suspicious.

Good. I think we have a mutually acceptable compromise developing here.

I do think it is possible that microlensing by stellar-mass DM objects
is obcured by other more energetic phenomena in QSOs, and that this
possibility should not be labelled a "just so" story. The preprint I
cited in the previous post is fairly optimistic that QSO studies are
approaching a point where they might make substantial new contributions
to the questions we seek to answer.

The very first reported microlensing event was related to a
multiply-lensed QSO. The estimated mass of the lens was on the order
of 10^-4.5 solar masses. The error bars bracketed the Discrete Fractal
prediction at 8 x 10^-5 solar masses.

Let's not forget about microlensing studies closer to home, too.
Observational astrophysicists, for whom I have the greatest respect,
are, or will be, looking at the Bulge, Disk, Halo, globular clusters,
LMC, SMC, M31, etc., over the next 10 years.

I think we can look forward to an exciting time, one way or the other.

Robert Oldershaw