research summary
My work has been somewhat focused on the history and philosophy of spacetime physics. Often, my approach is to presuppose the general theory of relativity and then deduce various theorems of philosophical interest.
history
One
paper provides a coherent ontological account of force within Cartesian physics. I argue that the account is consistent with Descartes' writings and avoids certain problems found in previous interpretations.
Another
article (with Jim Weatherall) argues against Reichenbach's famous claim that the geometry of spacetime is merely a convention. The upshot is a no-go theorem demonstrating the impossibility of the project under reasonable assumptions.
Finally, I have a project which concerns Gödel's argument for the ideality of time. In opposition to the standard view, I defend Gödel's claim that the existence of possible worlds which contain no objective time lapse does indeed shed light on the nature of time in our own world.
determinism
One current
project explores the relationship between the related spacetime concepts of singularities and holes (types of barriers to determinism). I show one sense in which holes are necessarily singularities. I also introduce various distinctions concerning other types of singularities.
An earlier
paper examines holes in particular. I show that, under definitions found in the literature, holes can exist even in deterministic spacetimes. I introduce a reformulation of the concept of holes which avoids this consequence. I also contend that it is not yet clear that holes in a spacetime necessarily render it physically unreasonable.
I also have two survey-style papers concerning the global structure of spacetime. The
first illustrates how one can, using the relevant formalism, pose and answer various questions concerning topics such as determinism. The
second is a longer, more technical version of the first.
acausality
One
paper of mine considers a particular definition of a 'time machine' found in the literature. It has been conjectured that under this definition, the class of models containing a time machine is not empty. I prove the conjecture.
In a related
article, I provide a counterexample to a much discussed time machine no-go result. Additionally, I prove a positive statement: a time machine existence theorem under a modest "no holes" assumption.
In another
paper, I examine Gödel spacetime. In this model, time travel is possible but only with enough fuel. I show that one can time travel in Gödel spacetime with less fuel than was previously known. A related, less technical paper is available
here.
Also, I have a
peice which investigates a consequence of certain acausal spacetimes: the possibility of supertasks. Some have articulated various ways in which such models (i.e. the Malament-Hogarth spacetimes) may be considered physically problematic. I examine these criticisms and investigate the prospect of escaping them.
underdetermination
I have one
article which considers the prospects of predicting events in spacetime. I propose a definition of prediction which seems to fully appreciate our epistemic predicament and demonstrate that, under this formulation, prediction is essentially impossible. The result is a consequence of a type of underdetermination of global structure.
A second
piece investigates observationally indistinguishable spacetimes. I prove that, excluding certain pathological examples, every cosmological model of our universe is observationally indistinguishable from some other model. Additionally, I show that even if one assumes a principle of uniformity - that the physical laws we determine locally are applicable throughout the universe - these general epistemological difficulties remain.
A third
paper suggests that what counts as a physically reasonable cosmological model is strongly tied to our epistemic situation. Cosmologists often use certain global properties to exclude 'physically unreasonable' cosmological models from serious consideration. But, on what grounds should these properties be regarded unphysical if we cannot rule out, even with a robust type of inductive reasoning, the possibility of the properties obtaining in our own universe?