Dwarfs and dim galaxies mark limits of knowledge.

When 250 astronomers met in Cardiff early this month at the U.K. National Astronomy Meeting, sponsored by the Royal Astronomical Society and the Particle Physics and Astronomy Research Council, they grappled with some big problems, among them the age of the universe and its mass. They also took on an even bigger metaproblem: How confident can they be in their knowledge about cosmic origins?