|Prof. Leonard Susskind|
I get him now. He never looks stressed during questions because he knows everything. He makes the 'mistakes' because it keeps the audience awake and involved: those little cognitive dissonances. He stresses the big picture because that's the narrative which conveys the underlying concepts.
He is the perfect complement to the textbook.
His genius is even deeper. In early lectures he covers enough differential geometry for General Relativity. Differential geometry is hard: as I absorbed his lecture I kept thinking Riemann was a genius. And yet he conveyed the key concepts of generalised coordinates, the metric tensor, connections, curvature and geodesics perfectly. Ditto for tensor algebra and calculus. Truly the theoretical minimum!
Here are the ten lectures I'm referring to (YouTube playlist).
Yesterday Susskind told me about falling into a black hole using the Schwarzschild metric and coordinates. We started from the metric, integrated over a trajectory to get a distance, looked at the conditions under which this trajectory would be a geodesic (it's stationary) and then did some algebra to get velocity at various distances from the black hole from the viewpoint of a distant observer. We derived the well-known weird results that the object appears to stop at the event horizon and takes an infinite amount of time to get there. This is not the view of the freely-falling observer: the formal resolution of this puzzle is to come.