Steven Weinberg died day before yesterday. He shared the Nobel Prize with Abdus Salam and Sheldon Glashow for the unification of the electromagnetic and weak nuclear interactions, a key component of what later came to be called the Standard Model of particle physics. He's on anybody's short list of the most important physicists of the second half of the 20th century (Hawking's probably not).

When it came to style, though he was obviously brilliant, he was kind of the opposite of Richard Feynman. He was absolutely thorough, even exacting. His quantum field theory lectures were mind-numbing. I remember having to write constantly, almost never being able to stop to think.

It was the right mindset for coming up with the unification. It was an ugly theory. It was built on some beautiful pieces, like the basic ideas of symmetry groups and nonabelian gauge theory, some slightly less beautiful ones like the whole technology of quantum field theory calculations and renormalization or parity violation, and ugly, kludgy bits like the Higgs (et al.) mechanism. The prize went to the ones who didn't get bored with it and move on to other things, but kept taking those ideas seriously until they could fit them together in just the right way.

I did my first Ph.D. in the Weinberg Theory Group at UT-Austin. He was on my committee. He was one of the few in the old guard who made very serious attempts to learn string theory. He learned the string theory of the 80's, I imagine very well, but right around the mid-90's, with the Seiberg-Witten results and string duality and a serious increase in mathematical requirements, it was a bit much. Whenever one of the new results connected well with his enormous knowledge of and expertise in quantum field theory, he understood it well and even made use of it in his own work. But much of the time it didn't, and he would constantly say, "I don't understand" in seminars (and at my defense--which was fairly stress-inducing). A mark of a field that actually progresses is that it's the younger ones who are the experts in cutting-edge work (not grad students, with rare exceptions--it's the smart post-docs and junior faculty). Though I wouldn't call him a humble man, from my limited interaction with him, he definitely had the right kind of intellectual humility and was completely comfortable in his role as the guy who needed things explained to him (of course, there were always others in the seminar who needed that too, though they didn't always say so).

He remained enormously productive right to the end. His textbooks were like his lectures, thorough and complete, but not for me. I read many of his popular books, though. Like Freeman Dyson, he was enormously erudite in areas outside physics; unlike Dyson, he was sensible. I was pretty much (though obviously not 100%) in agreement with him on atheism, religion, rationalism, and reductionism, but pretty much not on politics.