Quantum philosophy

Roland OmneÁ s is well known as an elementary particle theoretician, and for his detailed and comprehensive books The Interpretation of Quantum Mechanics (Princeton, 1994 ) and Understanding Quantum Mechanics (Princeton, 1999 ). Now he presents his ideas on quantum mechanics in a less technical way within a much wider framework. The title Quantum Philosophy indicates that it is concerned with the debates on the interpretation of quantum mechanics which have raged ever since the monumental battles between Bohr and Einstein. Although the positivism associated with Bohr’ s Copenhagen interpretation is now largely abandoned by philosophers [1], Bohr’ s views are still widely, although often uncritically, accepted among physicists, and to a much lesser extent among philosophers of quantum mechanics [2]. The views on the Bohr ± Einstein debate range from `Bohr wins, Einstein loses’ [3] to `the Bohr ± Einstein debate has already been resolved, and in favour of Einstein’ [4]. OmneÁ s’ main theme is that `one day, the principles of science will be so close to the heart and the essence of things that the philosophy of knowledge will be able to ® nd in them its own foundations’ . According to OmneÁ s, `such a day has arrived’ . There is a crisis in epistemology: `the philosophical re ̄ ection about science has lost its way Ð or stagnates. The fashionable authors see only uncertainties, paradigms without enduring principles, an absence of method, and a presence of erratic revolutions, precisely when we should be trumpeting the success of science whose extent and consistency are unprecedented’ . Much of the book surveys the history of the rise of formalism in physics while the latter part `shows how to loosen that formalism and overcome it’ . This makes it possible to resolve the di culties, and in the end it all turns out to be quite simple. Common sense is recovered and thus, despite its formal aspects, `science brings with it a theory of knowledge, once again transparent, that can explain how we humans understand the world’ . His main concern is the connection between the reversible, probabilistic microscopic quantum world and the irreversible, deterministic, macroscopic classical world. It claims to solve the problems of the infamous boundary, the paradoxes inherent in the introduction of quantum probabilities into the macroscopic world, and the direction of time. This advance in conceptual understanding has been achieved by the decoherent (or consistent) histories approach to quantum mechanics initiated by Gri ths in 1984 [5] and independently proposed by OmneÁ s himself in 1988 [6]. Later on it was rediscovered and extended by GellMann and Hartle [7]. The account is set within the wider historical and mathematical context of the many attempts to attain a consistent account of the microscopic and macroscopic worlds. It is presented verbally, with very few formulae and (astonishingly ) no references to the original papers. The ® rst chapter contains a review of the classical logic of the ancient Greeks. This is followed by a survey of classical physics, including astronomy from Hipparchus to Kepler, the dawn of mechanics, Newton’ s dynamics, electromagnetism and Maxwell’ s equations. The third chapter is on classical mathematics from the time of Pythagoras and Euclid to the giants of the nineteenth century, Gauss, Cauchy, Riemann, Weierstrass and many others. Particular problems were posed by the concept of in® nity, and these were tackled by Dedekind and Cantor. Another strand in the development of understanding is the philosophy of knowledge, the subject of the fourth chapter. A start was made by Plato in his Theaetetus, but it Dr P. E. Hodgson is at Department of Nuclear Physics, Univers ity of Oxford, Oxford, UK. Contemporary Physics, 2000, volume 41, number 2, pages 105± 108