In this illuminating book, the renowned theoretical physicist Lee Smolin argues that fundamental physics -- the search for the laws of nature -- losing its way. Ambitious ideas about extra dimensions, exotic particles, multiple universes, and strings have captured the public's imagination -- and the imagination of experts. But these ideas have not been tested experimentally, and some, like string theory, seem to offer no possibility of being tested. Yet these speculations dominate the field, attracting the best talent and much of the funding and creating a climate in which emerging physicists are often penalized for pursuing other avenues. As Smolin points out, the situation threatens to impede the very progress of science. With clarity, passion, and authority, Smolin offers an unblinking assessment of the troubles that face modern physics -- and an encouraging view of where the search for the next big idea may lead.