In article ,
" writes:

Phillip Helbig---remove CLOTHES to reply wrote:

I posted some references earlier in a similar thread which definitively
show that microlensing canNOT be the dominant cause of QSO variability.
However, if these objects exist as you claim, then they should cause
significant QSO variability through microlensing, at a level roughly
corresponding to the observed variability. Your theory made a
prediction and it was falsified. Good theory, but wrong. Move on. You
can only save your theory by "adjusting" it, by making an ad-hoc claim
that this dark matter is distributed so that it won't cause QSO
microlensing. What was your term? Epicycle.

Well, clearly we have a difference of opinion here.

My theory will not be adjusted; I stand by the predictions I have made.
I think your claim that it has been ruled out is more than a little
premature. I think it would be wiser and more scientifically
appropriate to keep an open mind in this area. These are very
challenging observations which require a lot of simplifications and
assumptions in order to come up with take-home results. It is not
surprising that the early results in the various microlensing
experiments have had various levels of uncertainty.

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.