The role of probability is one of the most contested issues in the interpretation of contemporary physics. In this paper, I’ll be reevaluating some widely held assumptions about where and how probabilities arise. Larry Sklar voices the conventional wisdom about probability in classical physics in a piece in the Stanford Online Encyclopedia of Philosophy, when he writes that “Statistical mechanics was the first foundational physical theory in which probabilistic concepts and probabilistic explanation played a fundamental role.” And the conventional wisdom (...) about quantum probabilities is that they are basic, not reducible to the types of probabilities we see in statistical mechanics. In the first section of this paper, I’ll argue that in fact classical physics was steeped in probability long before statistical mechanics came on the scene, specifically, that an objective measure over phase space is an indispensable component of any informative physical theory. In the next section, I’ll argue that this objective measure is the fundamental form of physical probability and that quantum probabilities can be defined in terms of it. In the last, I’ll raise some questions about the metaphysical status of the fundamental measure. (shrink)

This paper comments on a paper by Chris Fuchs. Both papers are to appear in "New Directions in the Philosophy of Science", eds. M. C. Galavotti, S. Hartmann, M. Weber, W. Gonzalez, D. Dieks and T. Uebel. This paper presents some mild criticisms of Fuchs's views, some based on the EPR and Wigner's friend scenarios, and some based on the quantum theory of measurement. A few alternative suggestions for implementing a subjectivist interpretation of probability in quantum mechanics conclude the paper.

This is a philosophical paper in favor of the many-worlds interpretation of quantum theory. The necessity of introducing many worlds is explained by analyzing a neutron interference experiment. The concept of the “measure of existence of a world” is introduced and some difficulties with the issue of probability in the framework of the MWI are resolved.

First para: Before the 17th century, there was not much discussion, and little uniformity in conception, of natural laws. The rise of science in 17th century, Newton’s mathematization of physics, and the provision of strict, deterministic laws that applied equally to the heavens and to the terrestrial realm had a profound impact in transforming the philosophical imagination. A philosophical conception of physical law built on the example of Newtonian Mechanics became quickly entrenched. Between the 17th and 20th centuries, there was (...) a great deal of philosophical interest in probabilities, but probabilities were mostly regarded as having something to do with the management of opinion, not as having a fundamental role in science. Probabilities made their first appearance in an evidently ineliminable way in the laws of a fundamental theory with the advent of quantum mechanics. Quantum probabilities have come to be called ‘chances’ in the philosophical literature, and their interpretation has been one of the central problems in philosophy of science now for almost a century. There continue to be hold-outs that insist that there must be an underlying probability-free replacement for quantum mechanics and Bohmians have had some success in formulating a deterministic alternative to quantum mechanics, but most physicists accept that the probabilistic character of the quantum mechanical laws is likely to be retained in any successor theory. While physics has adjusted itself comfortably to the existence of ineliminably probabilistic laws, philosophy has not managed arrive at a stable interpretation of quantum probability. The difficulty is that there are a number of constraints that an interpretation of chance must satisfy, constraints that appear to be partially definitive of the concept and it proves to be extraordinarily difficult to meet them simultaneously. (shrink)