September 3, 2001 Publications Michael Riordan Michael Riordan, adjunct professor of physics, published a review in the New York Times Book Review of a new book by physicist Lee Smolin, Three Roads to Quantum Gravity. The book discusses how scientists are trying to bring together the insights from quantum mechanics and Einstein's general theory of relativity into a single unified theory of physics. "It is one of the most difficult intellectual challenges humanity has ever faced," Riordan wrote in his review. He noted that the goal of combining these two theories eluded physicists for most of the 20th century, but that there has been progress in recent decades.