If the models for cosmology and structure formation on which
Table 1 is based could be taken as given, the only uncertainties
being the astronomy, the
constraints on the cosmological parameters would be clear.
The long list of evidence for
_{m} = 0.25 ±
0.10, in the table and the new results from the SNeIa redshift-magnitude
relation and weak lensing, abundantly demonstrates that we live
in a low density universe. The CBR demonstrates space
sections are flat. Since
_{m} is small there has
to be a term in the stress-energy tensor that acts like Einstein's
cosmological constant. The SNeIa redshift-magnitude result favors
a low density flat universe over low density with open geometry
( = 0), at about three
standard deviations. That alone is not compelling, considering
the hazards of astronomy, but it is an impressive check of what
the CBR anisotropy says.

But we should remember that all this depends on models we are
supposed to be testing. The dynamical estimates of
_{m} in lines 1a and 1b
assume the inverse square law of gravity. That is appropriate,
because it follows from the relativistic cosmology we are
testing. We have a check on this aspect of the theory, from
consistency with
other observations whose theoretical interpretations depend on
_{m} in other ways. The
CDM model fitted to observed large-scale structure requires a value of
_{m} that agrees with
dynamics. This elegant result was an
early driver for the adoption of the low density CDM model.
But we can't use it as evidence
for both the CDM model and the inverse square law;
we must turn to other measures. We have two beautiful
new results, from weak lensing and the redshift-magnitude relation, that
agree with
_{m} ~ 0.25. The latter
does not exclude
_{m} =
_{baryons} ~ 0.04; maybe MOND
accounts for flat *v*_{c}(*r*) but does not affect
equation (6)
(McGaugh 2000).
And if we modified
local Newtonian dynamics we might want to modify the physics of
the gravitational deflection of light.

There are alternative fits to the CBR anisotropy, with new physics (McGaugh 2000), or conventional physics and an arguably desperate model for early structure formation (Peebles, Seager & Hu 2000). They certainly look a lot less elegant than conventional general relativity theory with the CDM model, but we've changed our ideas of elegance before.

In Section 4 I reviewed two issues in
structure formation that I think
challenge the CDM model. They may in fact only
illustrate the difficulty of interpreting observations of complex
systems. It's just possible that they will lead us to some radical
adjustment of the models for structure formation and/or
cosmology. I don't give much weight to this, because
it would mean the model led us to the right
_{m} for
the wrong reason. Relatively fine adjustments are easier to
imagine, of course. With them we must be prepared for fine
adjustments of the constraints on parameters such as
.

This is quite a tangled web. Progress in applying the many tests, including the mapping the CBR temperature and polarization, will be followed with close attention.

We have an impressive case for the Friedmann-Lemaître
cosmology, from the successful fit to the CBR anisotropy and the
consistency of the evidence for
_{m} ~ 0.25 from a broad
range of physics and astronomy. But the cosmological
tests certainly are not complete and unambiguous, and since
they depend on astronomy the program is not likely to be
closed by one critical measurement. Instead, we should expect
a continued heavy accumulation of evidence, whose weight will at
last unambiguously compel acceptance. We are seeing the
accumulation; we all look forward to the outcome.

**Acknowledgements**

This work was supported in part by the US National Science Foundation.