Out of Nowhere The Emergence of Spacetime in Theories of Quantum Gravity

The two fundamental pillars of physics for over 100 years have been quantum theory and general relativity, but their unification at short distances remains elusive, both technically and conceptually. This work is a philosophical investigation of the second kind of problem, and in particular of the striking fact that in many approaches to 'quantum gravity' classical spacetime structures are not merely quantized, but arguably absent—so that spacetime is not merely a classical limit, but 'emergent'. This issue is not only central to the problem of quantum gravity, but of deep significance for our philosophical understanding of physical reality, promising a conceptual revolution at least as profound as Einstein's.

Nick Huggett and Christian Wüthrich explore the question of spacetime emergence, for philosophers of metaphysics and science, and argue for spacetime functionalism as the answer to seeing how something non-spatiotemporal could ever appear as space and time. More technical chapters investigate the issue in detail for causal set theory, loop quantum gravity, and string theory, and the book also serves as a philosophical introduction to those theories for philosophers of physics. Out of Nowhere helps physicists clarify what new conceptual framework—not resting on space and time—may be necessary to achieve a theory of quantum gravity. This book also shows philosophers how the world may not be spatiotemporal at root, and what kind of a world we might then live in.

Preface1. Introduction: the emergence of spacetime2. Spacetime functionalism3. Spacetime from causality: causal set theory4. The emergence of spacetime from causal sets5. The road to loop quantum gravity6. The disappearance and emergence of spacetime in loop quantum gravity7. A string theory primer8. Duality9. The string theoretic account of general relativity10. The 'emergence' of spacetime in string theory11. Conclusion: whence spacetime?Bibliography