David AlbertDavid Z. Albert is a philosopher of physics at Columbia University. He has written three books, Quantum Mechanics and Experience (1992), Time and Chance (2000) and After Physics (2015). His first book combined an elementary description of quantum mechanics with a detailed look at several problems or puzzles that remain at the forefront of the conceptual foundations of quantum mechanics. He describes the principle of superposition, which he says is what distinguishes most importantly the quantum mechanical picture of the world from the classical one, and which is where everything that’s puzzling about quantum mechanics comes from. He then introduces the standard quantum-mechanical formalism and outlines the conventional wisdom about how one ought to think about that formalism. He claims that the Einstein-Podolsky-Rosen Paradox was "undercut" by John Bell. He says that Bell’s discovery is very frequently misunderstood, that Bell discovered something not merely about "hidden-variable" theories but also about quantum mechanics (and also about the world). He reviews the "measurement problem" and the involvement of a conscious observer. He then gives an account and a critique of the idea of the collapse of the wave function (with a detailed discussion of Ghirardi, Rimini, and Weber's "spontaneous collapse.") Next he considers the "many-worlds" theory of Hugh Everett, which was elaborated in recent years as the "multiverse" theory of Max Tegmark. Albert then examines a completely deterministic replacement for quantum mechanics due to Louis de Broglie, David Bohm, and John Bell. Albert's second book, Time and Chance, discusses many classic problems in thermodynamics and quantum mechanics, starting with the "arrow of time." He says he has made an "unprecedentedly careful discussion" with "unprecedentedly precise language of physical states" of what it means for a set of dynamical laws to distinguish, or to fail to distinguish, between the past and the future. He then describes the second law of thermodynamics and heat engines, whose entropy increase is (statistically) always in the future time direction. He explains Ludwig Boltzmann's development of statistical mechanics, with what he describes as a relatively novel discussion of the mathematical structure and the metaphysical status of the probability distributions over initial conditions and of the connection between entropy and information. He examines two famous paradoxes of classical statistical mechanics, the problem of microscopic irreversibility known as Loschmidt's paradox, and the problem of macroscopic recurrencedue to Ernst Zermelo and Henri Poincaré. He proposes a remedy for these paradoxes that he calls a new and fundamental and non-dynamical law of nature that he dubs the "past hypothesis" (the idea that the universe began in a state of low entropy or high information.) He then criticizes the claim that there cannot be such a thing as an "operational" Maxwell's demon." He argues, by means of an exclusive construction, that there is nothing whatsoever in either the classical or the quantum-mechanical laws of physics that stands in the way of there being such a demon as that. Finally, in what he describes as his most ambitious effort, he tries show the time-directedness of our own capacity to acquire information about the world, and to manipulate the world according to our will, or (more precisely) it is about the business of incorporating those sorts of directedness into the general picture of the world laid out thus far. Albert's third book, After Physics, is a collection of eight essays on the foundations of quantum mechanics (the basic quantum-mechanical formalism of wave functions and state vectors and Hermitian operators, nonlocality, the measurement problem, the Ghirardi-Rimini-Weber [GRW] theory, Bohmian mechanics, the many-worlds interpretation of quantum mechanics, and so on)—the sort of material that can be found in his first book. One essay is an extended discussion of his "Path Hypothesis" and our knowledge of the external world.
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