A traditional school in high energy physics is held in Brazil every two years. It is addressed to graduate students and young researchers in field theory, phenomenology and experimental high energy physics. This year the Swieca School took place in Campos do Jordão from January 21 to February 2. I went for the last week. The program and some lecture notes can be found here.
The first week was dedicated to introductory courses while the second week to advanced ones. On the theoretical side we had in the second week Gerard t'Hooft talking about unitarity in perturbative field theory, Hiroshi Ooguri lecturing on topological strings, and Kostas Skenderis on AdS/CFT. At the end of the day there was a discussion session with all lecturers present.
By far, Gerard's lectures was the most attractive of them all. He was talking about conventional field theory and how to group together diagrams to show unitarity. He was very patient and gentle when answering questions, even the most elementary ones. He touched many historical developments in field theory, like dispersion relations, the decay of π0 into two γ's and the chiral anomaly, and even string theory in its old days. In the discussion session most of the questions was addressed to him. Many interesting comments pop out . It was very interesting to see a Nobel prize commenting on many aspects of quantum field theory and even string theory. At a certain point he was asked to comment about the statement usually heard that a black hole in a quantum gravity theory is the analogue of the hydrogen atom in quantum mechanics. He remarked that this would be true for the Schwarzschild black hole and added that no quantum gravity theory is available. Kostas said that we can understand black holes in string theory in terms of D-branes. This was a moment of tension between the two. Gerard replied that only BPS black holes have such a description and that the real challenge is to describe the Schwarzschild black hole. Kostas then said that Schwarzschild black holes are technically very difficult to be treated but Gerard insisted that it may not be a technical problem but a matter of principle. That was the only tense moment in the school. And maybe Gerard has a point here.