Joseph Polchinski

“My greatest failure as head of the Theory Group here in Austin was to lose Joe to Santa Barbara.”

“And then, on October 5, 1995, a paper appeared that changed the whole discussion, forever. It was Joe, explaining D-branes to those of us who’d barely heard of his earlier work, and showing that many of these black holes, black strings and black surfaces were actually D-branes in disguise. His paper made everything clearer, simpler, and easier to calculate; it was an immediate hit. By the beginning of 1996 it had 50 citations; twelve months later, the citation count was approaching 300.”

“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.”

“In all there are four arguments here for the multiverse: the failure of conventional methods for understanding why the cosmological constant is not large, the success of the environmental theories for doing so, the successful prediction of the nonzero cosmological constant, and the string landscape.”

“In the open string the gauge charges are carried by the Chan-Paton degrees of freedom at the endpoints. In the closed string the charges are carried by fields that move along the string.”

“D-branes provide a simple description of various nonperturbative objects required by string duality, and give new insights into the quantum mechanics of black holes and the nature of spacetime at the shortest distances. ... D-branes are extended objects, topological defects in a sense, defined by the property that strings can end on them.”