John Earman

These provocative essays by leading philosophers of science exemplify and illuminate the contemporary uncertainty and excitement in the field. The papers are rich in new perspectives, and their far-reaching criticisms challenge arguments long prevalent in classic philosophical problems of induction, empiricism, and realism. By turns empirical or analytic, historical or programmatic, confessional or argumentative, the authors' arguments both describe and demonstrate the fact that philosophy of science is in a ferment more intense than at any time since the heyday of logical positivism early in the twentieth century. Contents: "Thoroughly Modern Meno," Clark Glymour and Kevin Kelly "The Concept of Induction in the Light of the Interrogative Approach to Inquiry," Jaakko Hintikka "Aristotelian Natures and Modern Experimental Method," Nancy Cartwright "Genetic Inference: A Reconsideration of "David Hume's Empiricism," Barbara D. Massey and Gerald J. Massey "Philosophy and the Exact Sciences: Logical Positivism as a Case Study," Michael Friedman "Language and Interpretation: Philosophical Reflections and Empirical Inquiry," Noam Chomsky "Constructivism, Realism, and Philosophical Method," Richard Boyd "Do We Need a Hierarchical Model of Science?" Diderik Batens "Theories of Theories: A View from Cognitive Science," Richard E. Grandy "Procedural Syntax for Theory Elements," Joseph D. Sneed "Why Functionalism Didn't Work," Hilary Putnam "Physicalism," Hartry Field

The idea that the quantum probabilities are best construed as the personal/subjective degrees of belief of Bayesian agents is an old one. In recent years the idea has been vigorously pursued by a group of physicists who fly the banner of quantum Bayesianism. The present paper aims to identify the prospects and problems of implementing QBism, and it critically assesses the claim that QBism provides a resolution of some of the long-standing foundations issues in quantum mechanics, including the measurement problem and puzzles of nonlocality.

David Lewis' "Principal Principle" is a purported principle of rationality connecting credence and objective chance. Almost all of the discussion of the Principal Principle in the philosophical literature assumes classical probability theory, which is unfortunate since the theory of modern physics that, arguably, speaks most clearly of objective chance is the quantum theory, and quantum probabilities are not classical probabilities. Given the generally accepted updating rule for quantum probabilities, there is a straight forward sense in which the Principal Principle is a theorem of quantum probability theory for any credence function satisfying a suitable additivity requirement. No additional principle of rationality is needed to bring credence into line with objective chance.

David Lewis' "Principal Principle" is a purported principle of rationality connecting credence and objective chance. Almost all of the discussion of the Principal Principle in the philosophical literature assumes classical probability theory, which is unfortunate since the theory of modern physics that, arguably, speaks most clearly of objective chance is the quantum theory, and quantum probabilities are not classical probabilities. This paper develops an account of how chance works in quantum theory that reveals a connection between credence and quantum chance quite unlike what is envisioned in the philosophical literature: as a theorem of quantum probability, updating a completely additive chance function on a knowledge of chance brings credence into line with chance. The account also suggests a way of construing the Humean supervenience of chance that has the virtue of dissolving some puzzles about the "undermining" of chances. A number of interpretative moves in quantum theory are needed to generate the account of quantum chance on offer here, and they can all be disputed. But engaging in these disputes is part and parcel of naturalized metaphysics, and as such it can be more productive than engaging in the battle of intuitions among analytical metaphysicians about how chance ought to work this and other possible worlds.

We address the question of whether it is possible to operate a time machine by manipulating matter and energy so as to manufacture closed timelike curves. This question has received a great deal of attention in the physics literature, with attempts to prove no- go theorems based on classical general relativity and various hybrid theories serving as steps along the way towards quantum gravity. Despite the effort put into these no-go theorems, there is no widely accepted definition of a time machine. We explain the conundrum that must be faced in providing a satisfactory definition and propose a resolution. Roughly, we require that all extensions of the time machine region contain closed timelike curves; the actions of the time machine operator are then sufficiently "potent" to guarantee that closed timelike curves appear. We then review no-go theorems based on classical general relativity, semi-classical quantum gravity, quantum field theory on curved spacetime, and Euclidean quantum gravity. Our verdict on the question of our title is that no result of sufficient generality to underwrite a confident "yes" has been proven. Our review of the no-go results does, however, highlight several foundational problems at the intersection of general relativity and quantum physics that lend substance to the search for an answer

It generally agreed that the requirement of formal general covariance is a condition of the well-formedness of a spacetime theory and not a restriction on its content. Physicists commonly take the substantive requirement of general covariance to mean that the laws exhibit diffeomorphism invariance and that this invariance is a gauge symmetry. This latter requirement does place restrictions on the content of a spacetime theory. The present paper explores the implications of these restrictions for interpreting the ideology and ontology of classical general relativity theory and loop quantum gravity.

On Itamar Pitowsky’s subjective interpretation of quantum mechanics, “the Hilbert space formalism of quantum mechanics [QM] is just a new kind of probability theory”, one whose probabilities correspond to odds rational agents would accept on the outcomes of gambles concerning quantum event structures. Our aim here is to ask whether Pitowsky’s approach can be extended from its original context, of quantum theories for systems with an finite number of degrees of freedom, to systems with an infinite number of degrees of freedom, such as quantum field theory and quantum statistical mechanics in the thermodynamic limit. An impediment to generalization is that Pitowsky adopts the framework of event structures encoded by atomic algebras, whereas the algebras typical of QM for infinitely many degrees of freedom are usually non-atomic. We describe challenges to Pitowsky’s approach deriving from this impediment, and sketch and assess strategies Pitowsky might use to meet those challenges. Although we offer no final verdict about the eventual success of those strategies, a testament to the worth of Pitowsky’s approach is that attempting to extend it engages us in provocative foundational issues.

I have argued that the most recent versions of the causal theory are subject to serious limitations. The causal analysis of spatiotemporal coincidence considered in Section IV does not apply to space-times in which (1) fails. And current versions of the theory collapse altogether for typical cases of relativistic space-times which are closed in their temporal aspects. Second, I have pointed out that the program of recent causal theorists is based on a false dichotomy — open vs. closed times; for only a small subclass of relativisitic space-times can be said to be either open or closed in their temporal aspects, and the causal theory seems incapable of handling the cases which fall in between. Third, I have argued that the general theory of relativity does not provide motivation for the causal theory; on the contrary, general relativity promotes the view of spacetime as a substantial entity.As a result, I do not see that the causal theorist has a convincing argument against the position which holds that in order to understand the subtle and complex temporal structures encompassed by relativity theory, one must accept space-time as an entity which cannot be analyzed away as an abstract mathematical construct used for representing the ‘physical’, i.e., causal, relations between events. And I cannot agree with van Fraassen (1970, p. 140) that Philosophers were not long in appreciating this development [i.e., relativity theory], and the consequent construction of the causal theory of time and space-time must be considered one of the major contributions of twentieth-century philosophy of science. For it seems to me that causal theorists have failed to appreciate this development and that the construction of the causal theory has served to obscure important and interesting facts about the temporal aspect of space-time

It is argued that the main problem with "the problem of the direction of time" is to figure out what the problem is or is supposed to be. Towards this end, an attempt is made to disentangle and to classify some of the many issues which have been discussed under the label of 'the direction of time'. Secondly, some technical apparatus is introduced in the hope of producing a sharper formulation of the issues than they have received in the philosophical literature. Finally, some tentative suggestions about the central issues are offered. In particular, it is suggested that entropy and irreversibility are much less crucial to the central issues than most philosophers would have us believe. This suggestion is not made because of any firm conviction of its correctness but rather because it helps to focus the discussion on some basic but long neglected assumptions which underlie traditional approaches

Time in electromagnetism shares many features with time in other physical theories. But there is one aspect of electromagnetism's relationship with time that has always been controversial, yet has not always attracted the limelight it deserves: the electromagnetic arrow of time. Beginning with a re-analysis of a famous argument between Ritz and Einstein over the origins of the radiation arrow, this chapter frames the debate between modern Einsteinians and neo-Ritzians. It tries to find a clean statement of what the arrow is and then explains how it relates to the cosmological and thermodynamic arrows, representing the most developed and sophisticated attack yet, in either the physics or philosophy literature, on the electromagnetic arrow of time.

In 1894 Pierre Curie announced what has come to be known as Curie's Principle: the asymmetry of effects must be found in their causes. In the same publication Curie discussed a key feature of what later came to be known as spontaneous symmetry breaking: the phenomena generally do not exhibit the symmetries of the laws that govern them. Philosophers have long been interested in the meaning and status of Curie's Principle. Only comparatively recently have they begun to delve into the mysteries of spontaneous symmetry breaking. The present paper aims to advance the discussion of both of these twin topics by tracing their interaction in classical physics, ordinary quantum mechanics and quantum field theory. The features of spontaneous symmetry that are peculiar to quantum field theory have received scant attention in the philosophical literature. These features are highlighted here, along with an explanation of why Curie's Principle, though valid in quantum field theory, is nearly vacuous in that context.

The importance of the Unruh effect lies in the fact that, together with the related Hawking effect, it serves to link the three main branches of modern physics: thermal/statistical physics, relativity theory/gravitation, and quantum physics. However, different researchers can have in mind different phenomena when they speak of “the Unruh effect” in flat spacetime and its generalization to curved spacetimes. Three different approaches are reviewed here. They are shown to yield results that are sometimes concordant and sometimes discordant. The discordance is disconcerting only if one insists on taking literally the definite article in “the Unruh effect.” It is argued that the role of linking different branches of physics is better served by taking “the Unruh effect” to designate a family of related phenomena. The relation between the Hawking effect and the generalized Unruh effect for curved spacetimes is briefly discussed.

Although C. D. Broad's notion of Becoming has received a fair amount of attention in the philosophy-of-time literature, there are no serious attempts to show how to replace the standard 'block' spacetime models by models that are more congenial to Broad's idea that the sum total of existence is continuously increased by Becoming or the coming into existence of events. In the Newtonian setting Broad-type models can be constructed in a cheating fashion by starting with a Newtonian block model, carving chips off the block, and assembling the chips in an appropriately structured way. However, attempts to construct Broad-type models in a non-cheating fashion reveal a number of problematic aspects of Becoming that have not received adequate attention in the literature. The paper then turns to an assessment of the problem and prospects of adapting Becoming models to relativistic spacetimes. The results of the assessment differ in both minor and major ways from the ones in the extant literature. Finally, the paper describes how the causal set approach to quantum gravity promises to provide a mechanism for realizing Becoming, though the form of Becoming that emerges may not conform to any of the versions discussed in the philosophical literature.

The philosophical literature on time and change is fixated on the issue of whether the B-series account of change is adequate or whether real change requires Becoming of either the property-based variety of McTaggart's A-series or the non-property-based form embodied in C. D. Broad's idea of the piling up of successive layers of existence. For present purposes it is assumed that the B-series suffices to ground real change. But then it is noted that modern science in the guise of Einstein's general theory poses a threat to real change by implying that none of the genuine physical magnitudes countenanced by the theory changes its value with time. The aims of this paper are to explain how this seemingly paradoxical conclusion arises and to assess the merits and demerits of possible reactions to it.