Given Hugh Everett III's understanding of the proper cognitive status of physical theories, his relative-state formulation of pure wave mechanics arguably qualifies as an empirically acceptable physical theory. The argument turns on the precise nature of the relationship that Everett requires between the empirical substructure of an empirically faithful physical theory and experience. On this view, Everett provides a weak resolution to both the determinate record and the probability problems encountered by pure wave mechanics, and does so in a way (...) that avoids unnecessary metaphysical complications. Taking Everett's goal to be showing the empirical faithfulness of the relative-state formulation agrees well with his characterization of his project as one of seeking a model for observation in the correlation structure described by pure wave mechanics and seeking a measure of typicality over this empirical substructure that covaries with our empirically warranted expectations. 1 Pure Wave Mechanics and Relative States2 Everett and Frank3 Everett on the Nature of Physical Theories4 Conditions for Empirical Faithfulness5 The Empirical Faithfulness of Pure Wave Mechanics6 Conclusion. (shrink)

Presents a guide to the basics of quantum mechanics and measurement.

A many-worlds interpretation is of quantum mechanics tells us that the linear equations of motion are the true and complete laws for the time-evolution of every physical system and that the usual quantum-mechanical states provide complete descriptions of all possible physical situations. Such an interpretation, however, denies the standard way of understanding quantum-mechanical states. When the pointer on a measuring device is in a superposition of pointing many different directions, for example, we are to understand this as many pointers, each (...) in a differentworld, each pointing in a different determinate direction. We ask here whether such talk makes any genuinely intelligible sense of the term world. We conclude that it does not. (shrink)

This work has been selected by scholars as being culturally important and is part of the knowledge base of civilization as we know it. This work is in the public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be (...) preserved, reproduced, and made generally available to the public. To ensure a quality reading experience, this work has been proofread and republished using a format that seamlessly blends the original graphical elements with text in an easy-to-read typeface. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant. (shrink)

It is demonstrated that neither the arguments leading to inconsistencies in the description of quantum-mechanical measurement nor those “explaining” the process of measurement by means of thermodynamical statistics are valid. Instead, it is argued that the probability interpretation is compatible with an objective interpretation of the wave function.

State-reduction and the notion of actuality are compared to passage through time and the notion of the present; already in classical relativity the latter give rise to difficulties. The solution proposed here is to treat both tense and value-definiteness as relational properties or facts as relations; likewise the notions of change and probability. In both cases essential characteristics are absent: temporal relations are tenselessly true; probabilistic relations are deterministically true. The basic ideas go back to Everett, although the technical development (...) makes use of the decoherent histories theory of Griffiths, Omnès, and Gell-Mann and Hartle. Alternative interpretations of the decoherent histories framework are also considered. (shrink)

The relational approach to tense holds that the now, passage, and becoming are to be understood in terms of relations between events. The debate over the adequacy of this framework is illustrated by a comparative study of the sense in which physical theories, (in)deterministic and (non)relativistic, can lend expression to the metaphysics at issue. The objective is not to settle the matter, but to clarify the nature of this metaphysics and to establish that the same issues are at stake in (...) the relational approach to value-definiteness and probability in quantum mechanics. They concern the existence of a unique present, respectively actuality, and a notion of identity over time that cannot be paraphrased in terms of relations. (shrink)

A variety of ideas arising in decoherence theory, and in the ongoing debate over Everett's relative-state theory, can be linked to issues in relativity theory and the philosophy of time, specifically the relational theory of tense and of identity over time. These have been systematically presented in companion papers (Saunders 1995; 1996a); in what follows we shall consider the same circle of ideas, but specifically in relation to the interpretation of probability, and its identification with relations in the Hilbert Space (...) norm. The familiar objection that Everett's approach yields probabilities different from quantum mechanics is easily dealt with. The more fundamental question is how to interpret these probabilities consistent with the relational theory of change, and the relational theory of identity over time. I shall show that the relational theory needs nothing more than the physical, minimal criterion of identity as defined by Everett's theory, and that this can be transparently interpreted in terms of the ordinary notion of the chance occurrence of an event, as witnessed in the present. It is in this sense that the theory has empirical content. (shrink)

SummaryThe history of quantum physics has been deeply conditioned by the change in scientific practice as a social activity during the past fifty years. As a result the theory has not been allowed full maturing; both its formal and empirical advances have not resulted in a comparable conceptual progress. The recasting of quantum theory thus appears as an epistemological necessity. One of the main aspects of this process is to clear quantum theory from its persisting classical connections in order to (...) endow it with an autonomous and intrinsic status. Problems related to the foundations, description, interpretation and approximations of quantum theory are considered in turn, and various recent works are reviewed which contribute to the proposed endeavour.RésuméL'histoire de la théorie quantique a été fortement conditionnée par les changements intervenus au cours des cinquante dernières années dans la pratique scientifique en tant qu'activité sociale. La théorie en conséquence n'a pu atteindre sa pleine maturité et ses développements à la fois formels et empiriques n'ont pas conduit à des progrès conceptuels comparables. La refonte de la théorie quantique apparaît ainsi comme une nécessitéépistémologique. L'un des principaux aspects de ce processus consiste à débarrasser la théorie quantique de ses persistantes attaches classiques, de façon à lui conférer un statut autonome et intrinsèque. On considère ici tour à tour les problèmes de fondements, de terminologie, d'interprétation et de limites, de la théorie quantique, tout en passant en revue divers travaux récents contribuant à l'entreprise proposée.ZusammenfassungDie Geschichte der Quantenphysik ist in entscheidender Weise durch die Veränderungen, die in den letzten fünfzig Jahren in der wissenschaftlichen Praxis als einer sozialen Tätigkeit eingetreten sind, bestimmt worden. Die Theorie hat deshalb ihre volle Reife nicht erlangen können; ihre zugleich formalen und empirischen Entfaltungen haben nicht zu einem entsprechenden begrifflichen Fortschritt geführt. Eine Umgestaltung der Quantentheorie muss daher als ein erkenntnistheoretisches Desiderat betrachtet werden. Einer der wichtigsten Aspekte eines derartigen Unterfangens wird darin bestehen, die Theorie von ihren hartnäckigen Bindungen an klassische Begriffe zu befreien, um ihr einen eigenständigen und autonomen Status zu verleihen. Es werden die Probleme der Begründung, der Terminologie, der Interpretation und der Grenzen der Quantentheorie diskutiert, indem auch verschiedene kürzlich erschienene Arbeiten, die sich auf das vorgeschlagene Unternehmen beziehen, berücksichtigt werden. (shrink)

Peter Byrne tells the story of Hugh Everett III (1930-1982), whose "many worlds" theory of multiple universes has had a profound impact on physics and philosophy. Using Everett's unpublished papers (recently discovered in his son's basement) and dozens of interviews with his friends, colleagues, and surviving family members, Byrne paints, for the general reader, a detailed portrait of the genius who invented an astonishing way of describing our complex universe from the inside. Everett's mathematical model (called the "universal wave function") (...) treats all possible events as "equally real", and concludes that countless copies of every person and thing exist in all possible configurations spread over an infinity of universes: many worlds. Afflicted by depression and addictions, Everett strove to bring rational order to the professional realms in which he played historically significant roles. In addition to his famous interpretation of quantum mechanics, Everett wrote a classic paper in game theory; created computer algorithms that revolutionized military operations research; and performed pioneering work in artificial intelligence for top secret government projects. He wrote the original software for targeting cities in a nuclear hot war; and he was one of the first scientists to recognize the danger of nuclear winter. As a Cold Warrior, he designed logical systems that modeled "rational" human and machine behaviors, and yet he was largely oblivious to the emotional damage his irrational personal behavior inflicted upon his family, lovers, and business partners. He died young, but left behind a fascinating record of his life, including correspondence with such philosophically inclined physicists as Niels Bohr, Norbert Wiener, and John Wheeler. These remarkable letters illuminate the long and often bitter struggle to explain the paradox of measurement at the heart of quantum physics. In recent years, Everett's solution to this mysterious problem - the existence of a universe of universes - has gained considerable traction in scientific circles, not as science fiction, but as an explanation of physical reality. (shrink)

"A leading scientist interweaves evolution, theoretical physics, and computer science to offer a new understanding of reality"--Cover.

An extraordinary and challenging synthesis of ideas uniting Quantum Theory, and the theories of Computation, Knowledge and Evolution, Deutsch's extraordinary book explores the deep connections between these strands which reveal the fabric ...

David Wallace argues that we should take quantum theory seriously as an account of what the world is like--which means accepting the idea that the universe is constantly branching into new universes. He presents an accessible but rigorous account of the 'Everett interpretation', the best way to make coherent sense of quantum physics.

What would it mean to apply quantum theory, without restriction and without involving any notion of measurement and state reduction, to the whole universe? What would realism about the quantum state then imply? This book brings together an illustrious team of philosophers and physicists to debate these questions. The contributors broadly agree on the need, or aspiration, for a realist theory that unites micro- and macro-worlds. But they disagree on what this implies. Some argue that if unitary quantum evolution has (...) unrestricted application, and if the quantum state is taken to be something physically real, then this universe emerges from the quantum state as one of countless others, constantly branching in time, all of which are real. The result, they argue, is many worlds quantum theory, also known as the Everett interpretation of quantum mechanics. No other realist interpretation of unitary quantum theory has ever been found. Others argue in reply that this picture of many worlds is in no sense inherent to quantum theory, or fails to make physical sense, or is scientifically inadequate. The stuff of these worlds, what they are made of, is never adequately explained, nor are the worlds precisely defined; ordinary ideas about time and identity over time are compromised; no satisfactory role or substitute for probability can be found in many worlds theories; they can't explain experimental data; anyway, there are attractive realist alternatives to many worlds. Twenty original essays, accompanied by commentaries and discussions, examine these claims and counterclaims in depth. They consider questions of ontology - the existence of worlds; probability - whether and how probability can be related to the branching structure of the quantum state; alternatives to many worlds - whether there are one-world realist interpretations of quantum theory that leave quantum dynamics unchanged; and open questions even given many worlds, including the multiverse concept as it has arisen elsewhere in modern cosmology. A comprehensive introduction lays out the main arguments of the book, which provides a state-of-the-art guide to many worlds quantum theory and its problems. (shrink)

Everett's relative-state formulation of quantum mechanics is an attempt to solve the measurement problem by dropping the collapse dynamics from the standard von Neumann-Dirac theory of quantum mechanics. The main problem with Everett's theory is that it is not at all clear how it is supposed to work. In particular, while it is clear that he wanted to explain why we get determinate measurement results in the context of his theory, it is unclear how he intended to do this. There (...) have been many attempts to reconstruct Everett's no-collapse theory in order to account for the apparent determinateness of measurement outcomes. These attempts have led to such formulations of quantum mechanics as the many-worlds, many-minds, many-histories, and relative-fact theories. Each of these captures part of what Everett claimed for his theory, but each also encounters problems. (shrink)

I make the case that the Universe according to unitary quantum theory has a branching structure, and so can literally be regarded as a "many-worlds" theory. These worlds are not part of the _fundamental_ ontology of quantum theory - instead, they are to be understood as structures, or patterns, emergent from the underlying theory, through the dynamical process of decoherence. That they are structures in this sense does not mean that they are in any way unreal: indeed, pretty much all (...) higher-level ontology in science, from tables to phonons to tigers, is likewise emergent. Unitary quantum theory is therefore a "many-worlds" theory without any modification of the mathematical structure of the theory: the Everett interpretation does not consist in adding worlds to the formalism, but in realising that they are there already. Our grounds for accepting the reality of those worlds is no more, but no less, than our grounds for accepting any other not-directly observable consequence of an empirically very successful theory. (shrink)

NGC 1300 (shown in figure 1) is a spiral galaxy 65 million light years from Earth.1 We have never been there, and (although I would love to be wrong about this) we will never go there; all we will ever know about NGC 1300 is what we can see of it from sixty-five million light years away, and what we can infer from our best physics. Fortunately, “what we can infer from our best physics” is actually quite a lot. To (...) take a particular example: our best theory of galaxies tells us that that hazy glow is actually made up of the light of hundreds of billions of stars; our best theories of planetary formation tell us that a sizable fraction of those stars.. (shrink)