According to recent arguments, the geodesic principle strictly interpreted is compatible with Einstein’s field equations only in pathologically unstable circumstances and, hence, cannot play a fundamental role in the theory. It is shown here that geodesic dynamics can still be coherently reinterpreted within contemporary relativity theory as a universality thesis. By developing an analysis of universality in physics, I argue that the widespread geodesic clustering of diverse free-fall massive bodies observed in nature qualifies as a universality phenomenon. I then show how this near-geodetic clustering can be explained despite the pathologies associated with strict geodesic motion in Einstein’s theory.

The logical theory of branching space-times, which provides a relativistic framework for studying objective indeterminism, remains mostly disconnected from discussions of space-time theories in philosophy of physics. Earman has criticized the branching approach and suggested “pruning some branches from branching space-time.” This article identifies the different—order-theoretic versus topological—perspective of both discussions as a reason for certain misunderstandings and tries to remove them. Most important, we give a novel, topological criterion of modal consistency that usefully generalizes an earlier criterion, and we introduce a differential-geometrical version of branching space-times as a non-Hausdorff (generalized) manifold.

Within philosophy of physics it is broadly accepted that presentism as an empirical hypothesis has been falsified by the development of special relativity. In this article, I identify and reject an assumption common to both presentists and advocates of the block universe and then offer an alternative version of presentism that does not begin from spatiotemporal structure, which is an empirical hypothesis, and which has yet to be falsified. While some features of familiar presentism are lost, a sufficient core remains to warrant the label (though I fear that labeling it “presentism” dooms the view).

I point out that some common folk wisdom about time reversal invariance in classical mechanics is strictly incorrect, by showing some explicit examples in which classical time reversal invariance fails, even among conservative systems. I then show that there is nevertheless a broad class of familiar classical systems that are time reversal invariant.

There has been a long-standing and sometimes passionate debate between physicists over whether a dynamical framework for quantum systems should incorporate not completely positive (NCP) maps in addition to completely positive (CP) maps. Despite the reasonableness of the arguments for complete positivity, we argue that NCP maps should be allowed, with a qualification: these should be understood, not as reflecting ‘not completely positive’ evolution, but as linear extensions, to a system’s entire state space, of CP maps that are only partially defined. Beyond the domain of definition of a partial-CP map, we argue, much may be permitted.

This article provides a new context for an established metaphysical debate regarding the problem of persistence. I contend that perdurance, a popular view about persistence which maintains that objects persist by having temporal parts, can be formulated in quantum mechanics due to the existence of a formal analogy between temporal and spatial location. However, this analogy fails due to a ‘no-go’ result which demonstrates that quantum systems cannot be said to have temporal parts in the same way that they have spatial parts. Therefore, if quantum mechanics describes persisting physical objects then those objects cannot be said to perdure.

We describe two anomalies in Bohm’s quantum theory that shed light on the notion of probability zero in quantum mechanics. In one anomaly the preferred reference frame may be discovered.

In this essay I consider whether the theory of organic chemistry is reducible to the theory of quantum chemistry. Using philosophical machinery developed by James Woodward, I characterize the understanding provided by both theories. Then I argue that there are systematic reasons to suspect that quantum chemistry is incapable of supporting some of the significant explanations, predictions, and applications underwritten by an understanding of theoretical organic chemistry. Consequently, even should quantum chemistry be ‘reducible to’ quantum physics in some suitable sense, there are good reasons to doubt that many of the significant results of organic chemistry could be reproduced by quantum chemistry alone.

I present a novel approach to the scholarly debate that has arisen with respect to the philosophical import one should infer from scientific accounts of phase transitions by appealing to a distinction between representation understood as denotation, and faithful representation understood as a type of guide to ontology. It is argued that the entire debate is misguided, for it stems from a pseudo-paradox that does not license the type of claims made by scholars and that what is really interesting about phase transitions is the manner by which they force us to rethink issues regarding scientific representation, idealizations, and realism.

The thermodynamics of computation assumes that computational processes at the molecular level can be brought arbitrarily close to thermodynamic reversibility and that thermodynamic entropy creation is unavoidable only in data erasure or the merging of computational paths, in accord with Landauer’s principle. The no-go result shows that fluctuations preclude completion of thermodynamically reversible processes. Completion can be achieved only by irreversible processes that create thermodynamic entropy in excess of the Landauer limit.