What is superstring theory and why is it important? Can superstrings offer the fulfilment of Einstein's lifelong dream of a Theory of Everything? Co-authored by one of the leading pioneers in superstrings, this book approaches these scientific questions, looking at the scientific research.

Beyond Einstein’s Gravity is a graduate level introduction to extended theories of gravity and cosmology, including variational principles, the weak-field limit, gravitational waves, mathematical tools, exact solutions, as well as cosmological and astrophysical applications. The book provides a critical overview of the research in this area and unifies the existing literature using a consistent notation. Although the results apply in principle to all alternative gravities, a special emphasis is on scalar-tensor and f(R) theories. They were studied by theoretical physicists from early on, and in the 1980s they appeared in attempts to renormalize General Relativity and in models of the early universe. Recently, these theories have seen a new lease of life, in both their metric and metric-affine versions, as models of the present acceleration of the universe without introducing the mysterious and exotic dark energy. The dark matter problem can also be addressed in extended gravity. These applications are contributing to a deeper understanding of the gravitational interaction from both the theoretical and the experimental point of view. An extensive bibliography guides the reader into more detailed literature on particular topics.

Einstein's gravity theory—his general theory of relativity—has served as the basis for a series of astonishing cosmological discoveries. But what if, nonetheless, Einstein got it wrong? Since the 1930s, physicists have noticed an alarming discrepancy between the universe as we see it and the universe that Einstein's theory of relativity predicts. There just doesn't seem to be enough stuff out there for everything to hang together. Galaxies spin so fast that, based on the amount of visible matter in them, they ought to be flung to pieces, the same way a spinning yo-yo can break its string. Cosmologists tried to solve the problem by positing dark matter—a mysterious, invisible substance that surrounds galaxies, holding the visible matter in place—and particle physicists, attempting to identify the nature of the stuff, have undertaken a slew of experiments to detect it. So far, none have. Now, John W. Moffat, a physicist at the Perimeter Institute for Theoretical Physics in Waterloo, Canada, offers a different solution to the problem. The cap­stone to a storybook career—one that began with a correspondence with Einstein and a conversation with Niels Bohr—Moffat's modified gravity theory, or MOG, can model the movements of the universe without recourse to dark matter, and his work chal­lenging the constancy of the speed of light raises a stark challenge to the usual models of the first half-million years of the universe's existence. This bold new work, presenting the entirety of Moffat's hypothesis to a general readership for the first time, promises to overturn everything we thought we knew about the origins and evolution of the universe.

A daring new vision of the quantum universe, and the scandals controversies, and questions that may illuminate our future--from Canada's leading mind on contemporary physics. Quantum physics is the golden child of modern science. It is the basis of our understanding of atoms, radiation, and so much else, from elementary particles and basic forces to the behaviour of materials. But for a century it has also been the problem child of science, plagued by intense disagreements between its intellectual giants, from Albert Einstein to Stephen Hawking, over the strange paradoxes and implications that seem like the stuff of fantasy. Whether it's Schrödinger's cat--a creature that is simultaneously dead and alive--or a belief that the world does not exist independently of our observations of it, quantum theory is what challenges our fundamental assumptions about our reality. In Einstein's Unfinished Revolution, globally renowned theoretical physicist Lee Smolin provocatively argues that the problems which have bedeviled quantum physics since its inception are unsolved for the simple reason that the theory is incomplete. There is more, waiting to be discovered. Our task--if we are to have simple answers to our simple questions about the universe we live in--must be to go beyond it to a description of the world on an atomic scale that makes sense. In this vibrant and accessible book, Smolin takes us on a journey through the basics of quantum physics, introducing the stories of the experiments and figures that have transformed the field, before wrestling with the puzzles and conundrums that they present. Along the way, he illuminates the existing theories about the quantum world that might solve these problems, guiding us toward his own vision that embraces common sense realism. If we are to have any hope of completing the revolution that Einstein began nearly a century ago, we must go beyond quantum mechanics as we know it to find a theory that will give us a complete description of nature. In Einstein's Unfinished Revolution, Lee Smolin brings us a step closer to resolving one of the greatest scientific controversies of our age.