Universe or Multiverse?

Recent developments in cosmology and particle physics, such as the string landscape picture, have led to the remarkable realization that our universe - rather than being unique - could be just one of many universes. The multiverse proposal helps to explain the origin of the universe and some of its observational features. Since the physical constants can be different in other universes, the fine-tunings which appear necessary for the emergence of life may also be explained. Nevertheless, many physicists remain uncomfortable with the multiverse proposal, since it is highly speculative and perhaps untestable. In this volume, a number of active and eminent researchers in the field - mainly cosmologists and particle physicists but also some philosophers - address these issues and describe recent developments. The articles represent the full spectrum of views, providing for the first time an overview of the subject. They are written at different academic levels, engaging lay-readers and researchers alike.Table of ContentsPart I. Overviews:1. Introduction and overview Bernard Carr2. Living in the multiverse Steven Weinberg3. Enlightenment, knowledge, ignorance, temptation Frank WilczekPart II. Cosmology and Astrophysics:4. Cosmology and the multiverse Martin J. Rees5. The anthropic principle revisited Bernard Carr6. Cosmology from the top down Stephen Hawking7. The multiverse hierarchy Max Tegmark8. The inflationary universe Andrei Linde9. A model of anthropic reasoning: the dark to ordinary matter ratio Frank Wilczek10. Anthropic predictions: the case of the cosmological constant Alexander Vilenkin11. The definition and classification of universes James D. Bjorken12. M/string theory and anthropic reasoning Renata Kallosh13. The anthropic principle, dark energy and the LHC Savas Dimopoulos and Scott ThomasPart III. Particle Physics and Quantum Theory:14. Quarks, electrons and atoms in closely related universes Craig J. Hogan15. The fine-tuning problems of particle physics and anthropic mechanisms John F. Donoghue16. The anthropic landscape of string theory Leonard Susskind17. Cosmology and the many worlds interpretation of quantum mechanics Viatcheslav Mukhanov18. Anthropic reasoning and quantum cosmology James B. Hartle19. Micro-anthropic principle for quantum theory Brandon CarterPart IV. More General Philosophical Issues:20. Scientific alternatives to the anthropic principle Lee Smolin21. Making predictions in a multiverse: conundrums, dangers, coincidences Anthony Aguirre22. Multiverses: description, uniqueness and testing George Ellis23. Predictions and tests of multiverse theories Don N. Page24. Observation selection theory and cosmological fine-tuning Nick Bostrom25. Are anthropic arguments, involving multiverses and beyond, legitimate? William R. Stoeger26. The multiverse hypothesis: a theistic perspective Robin Collins27. Living in a simulated universe John D. Barrow28. Universes galore: where will it all end? Paul DaviesIndex.