Dr. Robert Wald, the Charles A. Swift Distinguished Service Professor of Physics at the University of Chicago, discusses three major ingredients underlying general relativity—special relativity, which says that space and time comprise a single entity; the equivalence principle, which says that...

Dr. Heino Falcke, a professor of astroparticle physics and radio astronomy at Radboud University in Nijmegen, the Netherlands, discusses “Black Hole Horizons.” Falcke is a member of the Royal Netherlands Academy of Arts and Sciences. In 2011, he was awarded the Spinoza Prize, the top science...