Many Worlds?: Everett, Quantum Theory, & Reality

What does realism about the quantum state imply? What follows when quantum theory is applied without restriction, if need be, to the whole universe? These are the questions which an illustrious team of philosophers and physicists debate in this volume. All the contributors are agreed on realism, and on the need, or the aspiration, for a theory that unites micro- and macroworlds, at least in principle. But the further claim argued by some is that if you allow the Schrödinger equation unrestricted application, supposing the quantum state to be something physically real, then this universe is one of countlessly many others, constantly branching in time, all of which are real. The result is the many worlds theory, also known as the Everett interpretation of quantum mechanics. The contrary claim sees this picture of many worlds as in no sense inherent in quantum mechanics, even when the latter is allowed unrestricted scope and even given that the quantum state itself is something physically real. For this picture of branching worlds fails to make physical sense, let alone common sense, even on its own terms. The status of these worlds, what they are made of, is never adequately explained. Ordinary ideas about time and identity over time become hopelessly compromised. The concept of probability itself is brought into question. This picture of many branching worlds is inchoate, it is a vision, an error. There are realist alternatives to many worlds, some even that preserve the Schrödinger equation unchanged. Twenty specially written essays, accompanied by commentaries and discussions, examine these claims and counterclaims in depth. They focus first on the question of ontology, the existence of worlds (Part 1 and 2), second on the interpretation of probability (Parts 3 and 4), and third on alternatives or additions to many worlds (Parts 5 and 6). The introduction offers a helpful guide to the arguments for the Everett interpretation, particularly as they have been formulated in the last two decades.

Table of Contents:
Simon Saunders: Many Worlds: an Introduction 1. Why Many Worlds? 1: David Wallace: Decoherence and Ontology 2: Jim Hartle: Quasiclassical Realms 3: Jonathan Halliwell: Macroscopic Superpositions, Decoherent Histories, and the Emergence of Hydrodynamical Behaviour 2. Problems with Ontology 4: Tim Maudlin: Can the world be only wavefunction? 5: John Hawthorne: A metaphysician looks at the Everett interpretation James Ladyman: Commentary. Reply to Hawthorne: Physics Before Metaphysics Transcript 1: ontology 3. Probability in the Everett Interpretation 6: Simon Saunders: Chance in the Everett interpretation 7: David Papineau: A Scandal of Probability Theory 8: David Wallace: How to prove the Born rule 9: Hilary Greaves and Wayne Myrvold: Everett and Evidence 4. Critical Replies 10: Adrian Kent: One World versus Many: the Inadequacy of Everettian Accounts of Evolution, Probability, and Scientific Confirmation 11: David Albert: Probability in the Everett picture 12: Huw Price: Decisions, Decisions, Decisions: Can Savage Salvage Everettian Probability? Transcript 2: Probability 5. Alternatives to Many Worlds 13: Wojciech Zurek: Decoherence, Einselection, Envariance, and Quantum Darwinism: From Relative States to the Existential Interpretation 14: Jeffrey Bub and Itamar Pitowsky: Two dogmas about quantum mechanics Christopher Timpson: Commentary: Rabid Dogma? Comments on Bub and Pitowsky 15: Rudiger Schack: The Principal Principle and Probability in the Many-Worlds interpretation 16: Antony Valentini: Pilot-wave theory: many worlds in denial? Harvey Brown: Commentary: Reply to Valentini 6. Not Only Many Worlds 17: Peter Byrne: Everett and Wheeler, the Untold Story 18: David Deutsch: Apart from universes 19: Max Tegmark: Many Worlds in Context 20: Lev Vaidman: Time Symmetry and the Many-Worlds Interpretation Transcript 3: Not (only) many worlds Bibliography

About the Author :
Simon Saunders is Professor of Philosophy at the University of Oxford. Jon Barrett is a Research Fellow in the Physics department at the University of Bristol Adrian Kent is a Reader in Quantum Physics at the University of Cambridge David Wallace is a lecturer in Philosophy of Physics at the University of Oxford

Review :
`Review from previous edition written with great clarity by some of the best minds in contemporary foundations of physics ... a fine read, summarizing nicely the state of the art in one of the most radical no-collapse interpretations of quantum theory. ' Notre Dame Philosophical Reviews