Another factor, at least in theoretical physics, has been the terrible job market that persisted through the last 30 years of the 20th century (it seems to be better now, as sputnik era professors finally seem to be retiring). From around 1970-2000 there were only a handful of jobs per year in particle theory, and even average research universities were able to hire exceptional people. In many of those years, the new crop of PhDs from any one of the top programs could have filled every faculty opening in the country. A little arithmetic is enough to understand the consequent logjam, and why there are so many former theorists in finance, technology, even biology.
With professors spending so much time blogging for no payment, universities might wonder whether this detracts from their value. Although there is no evidence of a direct link between blogging and publishing productivity, a new study* by E. Han Kim and Adair Morse, of the University of Michigan, and Luigi Zingales, of the University of Chicago, shows that the internet's ability to spread knowledge beyond university classrooms has diminished the competitive edge that elite schools once held.
Top universities once benefited from having clusters of star professors. The study showed that during the 1970s, an economics professor from a random university, outside the top 25 programmes, would double his research productivity by moving to Harvard. The strong relationship between individual output and that of one's colleagues weakened in the 1980s, and vanished by the end of the 1990s.
The faster flow of information and the waning importance of location—which blogs exemplify—have made it easier for economists from any university to have access to the best brains in their field. That anyone with an internet connection can sit in on a virtual lecture from Mr DeLong means that his ideas move freely beyond the boundaries of Berkeley, creating a welfare gain for professors and the public.
Universities can also benefit in this part of the equation. Although communications technology may have made a dent in the productivity edge of elite schools, productivity is hardly the only measure of success for a university. Prominent professors with popular blogs are good publicity, and distance in academia is not dead: the best students will still seek proximity to the best minds. When a top university hires academics, it enhances the reputations of the professors, too. That is likely to make their blogs more popular.