I'm reading an interesting new book, Bursts by Albert-Laszlo Barabasi. It's just released today, but I scored an advance copy by virtue of sharing the same publisher. The basic idea is simple: human behavior obeys power laws! That is, things we occasionally do tend to be clustered together, rather than simply occurring with uniform probability. I can't vouch for either the truth or usefulness of the claims put forward in the book; we all know that power laws can be slippery things. But the stories related along the way are pretty amusing. (And there's a very spiffy web page.) I'll admit that I jumped right to a chapter in the middle that relates the correspondence between Einstein and Theodor Kaluza in the year 1919 and thereabouts. Kaluza had just come up with the idea that electromagnetism could be unified with gravity by hypothesizing an extra dimension of space -- a scenario now known as Kaluza-Klein theory, which underlies all the contemporary excitement about extra dimensions of space. Many crackpots like to assert that our contemporary system of scientific publishing is overly ossified and hierarchical, and that a modern-day Einstein would never be appreciated; the truth is close to the opposite, as back in those days you really needed endorsement from someone established to get your papers published. So Kaluza wrote to Einstein, who was originally enthusiastic about the idea, and they had a flurry of correspondence. Eventually (as I now know) Einstein cooled on the idea, and Kaluza left physics to concentrate on pure mathematics. A couple of years later, after getting nowhere with his own attempts to unify gravity and E&M, Einstein turned back to Kaluza's approach, and wrote him again, offering to present his paper to the academy. The book's interest is actually in the "burstiness" of the correspondence -- a flurry of letters back and forth in 1919, then silence, then the conversation resumed in 1921. I was struck by this paragraph, relating the growth of Einstein's celebrity after the eclipse expedition of 1919 provided evidence supporting general relativity.
[Einstein's] sudden fame had drastic consequences for his correspondence. In 1919, he received 252 letters and wrote 239, his life still in its subcritical phase, allowing him to reply to most letters with little delay. The next year he wrote many more letters than in any previous year. To the flood of 519 he received, we have record of his having managed to respond to 331 of them, a pace, though formidable, insufficient to keeping on top of his vast correspondence. By 1920 Einstein had moved into the supercritical regime, and he never recovered. The peak came in 1953, two years before his death, when he received 832 letters and responded to 476 of them.
Can you imagine what Einstein would have faced in the email era? One thing is for sure: he was a champion correspondent. He composed approximately 14,500 letters, more than one per day over the course of his adult life. Not for the first time, Einstein makes me feel like a slacker.