Joel Primack is distinguished professor of physics emeritus at the University of California, Santa Cruz. He is one of the principal originators and developers of the theory of cold dark matter, which has become the basis for the standard modern picture of structure formation in the universe. His most recent book is The New Universe and the Human Future, coauthored with Nancy Ellen Abrams. He is currently president of Sigma Xi and chair-elect of the Forum on Physics and Society of the American Physical Society.