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It is impressive to see how well the Friedmann-Lemaître model fits the full range of observations summarized in Table 2. We have to to bear in mind that many of the measurements still are open to discussion, however, and that the entries in category 2 depend on a model for structure formation that also has to be tested. Thus there is a large number of question marks (even though I believe I have been an easy grader). Perhaps the best lesson one might draw from the length of the discussion of Table 2 in Section 3 is that we theorists ought to resist the temptation to draw large conclusions from the latest observational reports; these are extraordinarily difficult measurements that we best praise by respectful cautious consideration.

I think we should also bear in mind that substantial parts of the left-hand column of Table 1 were formulated a full seven decades ago, and that much of the rest was driven by observational advances. That is, although we have many elegant new theoretical ideas in cosmology, we have little evidence in hand on which Nature has chosen.

The right-hand column of Table 1, that represents the observational constraints, is considerably longer than it would have been in a list made ten years ago, and ten years ago there would have been a lot more question marks in Table 2. We can be sure work in progress will produce a considerably tighter network of cosmological tests ten years from now. I see no reason to think the results will fail to support the Friedmann-Lemaître model, but that will be revealed in the fullness of time and a lot of hard work.


I am grateful to David Hogg, Wayne Hu, and Max Tegmark for stimulating discussions. This work was supported in part at the Princeton Institute for Advanced Study by the Alfred P. Sloan Foundation.