“On notable classmate was Dan Friedan. Friedan stunned me, and I think everyone else, at his Ph.D. seminar, when he showed that Einstein's equation, the basic equation of general relativity, could be interpreted in terms of one of the basic objects in QFT, the β function that governs the energy scale. I did not see what this could possibly mean, but a few years later it showed up as one of the key ideas in string theory.”