The nature of time, probability and quantum mechanics, philosophy of physics and metaphysics, especially issues involving the role of mathematical tools like symmetry in physics, and applying this formal apparatus to the philosophy of mind.
Cosmology, in particular applying the physics of elementary particles to the extremely hot and violent conditions of the early universe, and exploring deep questions about the big bang, the fate of our universe, and the hope for intelligent life (here or elsewhere)
Condensed matter systems at ultra low-temperature that show purely quantum phenomena – even on big scales (superfluidity, superconductivity, Bose-Einstein condensates); measurements in the quantum world; probing the foundations of quantum theory.
Many aspects of geometry, black holes, novel views on the evolution of the universe (was there something before the Big Bang?), the interplay and unification of general relativity and quantum physics, and science of consciousness.