Signatures of the Artist

This book provides a nonmathematical survey of the past half-century of research in particle physics, nuclear physics, and cosmology bearing on the physical conditions that allow our universe to support the development of structure and the origins of life. These conditions rely on a surprising number of tiny imperfections—deviations from perfect symmetry (i.e., symmetry violations), homogeneity, or predictability—that seem mysteriously fine-tuned. The emphasis here is on the intricate tapestry of elegant experiments that have revealed and quantified these imperfections, as well as on theoretical efforts to understand how the imperfections arose in the infant universe. Among the topics covered are: the dominance of matter over antimatter (i.e., matter–antimatter asymmetry); the existence and intermixing of three generations of quarks and leptons; the stability of hydrogen and synthesis of other elements essential for life; the longevity and energy budget of the universe; the remaining mysteries surrounding dark matter, dark energy, and the postulated inflationary expansion of space in the infant universe; the fundamental role of randomness in quantum mechanics, in generating the first biomolecules and in biological evolution; the apparent perching of the vacuum state in our universe on the edge between stability and meta-stability; and philosophical questions, including the possibility of a multiverse, surrounding the interpretation of a universe that exhibits such fine-tuning. On all of these issues, the book clarifies what we know and how we know it, as distinct from what we speculate and how we might test it.