In article , Eric Flesch
writes:

On Mon, 31 Dec 12, Phillip Helbig wrote:
analysis of a gravitational-lens survey is a huge undertaking, and the
fact that the cosmological parameters derived from it agree with those
from much simpler (at least conceptually) tests is a huge argument in
favour of the underlying assumptions being correct.

Agreed, although that "missing matter" is a required part of the
picture should put the spanner in, at least a little.

Very little. Actually, this seems to me the simplest explanation, since
otherwise the assumption is that all matter is visible. Dark matter is
seen by some pundits as an epicycle put in to save the appearances.
However, there is no reason to expect all matter to be visible by
default. Indeed, there is baryonic matter which is not in stars, which
was also considered "missing matter". Then it was detected (e.g. via
X-ray emission of hot gas in clusters). OK, due to constraints from
primordial nucleosynthesis, we now know that most of the dark matter is
non-baryonic but, again, it seems rather anthropocentric to believe that
all matter must be baryonic. We live on a planet, but we don't expect
all matter to be in planets. The difference is that we knew that stars
existed before starting to think about missing mass. If non-baryonic
matter had been detected before modern cosmology came into being, no-one
would consider non-baryonic matter to be strange.