Works in Progress
Locality and Branching for Everettian Quantum Field Theory (Joint work with Chip Sebens)
We clarify the sense in which Everettian quantum mechanics (or the many worlds interpretation) is local, by holding it to the standard of relativistic locality. This requires us to focus on the fundamental dynamics and be clear about how states are assigned to regions of space in relativistic quantum mechanics and quantum field theory. we show explicitly that Everettian quantum mechanics satisfies this standard. With this standard of locality, we defuse the metaphysical worry of the supposed non-locality of one recent account of the branching process, providing an account on which the relativistic locality of Everettian quantum mechanics is compatible with the global branching of the emergent multiverse.
The Time in Thermal Time (under review, draft available upon request!)
Preparing general relativity for quantization in the Hamiltonian approach leads to the `problem of time,' rendering the world fundamentally timeless. One proposed solution is the `thermal time hypothesis,' which defines time in terms of states representing systems in thermal equilibrium. On this view, time is supposed to emerge thermodynamically even in a fundamentally timeless context. Here, I develop the worry that the thermal time hypothesis requires dynamics -- and hence time -- to get off the ground, thereby running into worries of circularity.
Quasi-Stationarity: The Impossible Process (draft available upon request!)
An ubiquitously used idealization in physics, e.g. black hole physics, is quasi-stationarity. Prominently, Hawking (1975) employed this idealization in making his argument for black hole evaporation. The core idea is to assume that a system is evolving ‘so slowly’ that it can be modeled dynamically as a sequence of stationary systems. Here, I argue that quasi-stationary processes, taken literally, are impossible in the same vein as Norton’s (2016) evaluation of quasi-static processes. Furthermore, while Norton vindicates the widespread use of quasi-staticity by showing how this ‘impossible’ idealization can be readily ‘de-idealized’ for use in quotidian thermodynamical reasoning, I argue that Hawking’s (1975) argument for black hole evaporation cannot yet be justified in a similar fashion. One would need to provide a procedure for finding an approximately globally conserved energy via approximate Killing fields, but this remains an open question in general relativity.
Decoherence, Branching, and the Born Rule for a Mixed-State Everettian Multiverse (joint work with Eddy Keming Chen)
(under review, preprint available here)
In Everettian quantum mechanics, justifications for the Born rule appeal to self-locating uncertainty or decision theory. Such justifications have focused exclusively on a pure-state Everettian multiverse, represented by a wave function. Recent works in quantum foundations suggest that it is viable to consider a mixed-state Everettian multiverse, represented by a (mixed-state) density matrix. Here, we develop the conceptual foundations for decoherence and branching in a mixed-state multiverse, and extend the standard Everettian justifications for the Born rule to this setting. This extended framework provides a unification of 'classical' and 'quantum' probabilities, and additional theoretical benefits, for the Everettian picture.
Check, Please: De-idealizing De-idealization
It is doubtless that scientific inquiry inextricably involves the use of idealizations: for ease of calculation and representation, we assume the absence of friction, the perfect sphericity of cows, or the impeccable rationality of human beings. Idealizations are, strictly speaking, false. Yet they play a crucial role in many of our best sciences in representing all sorts of phenomena, from coffee cups to black holes. Much ink has thus been spilled over how to justify them. A predominant view focuses on justifying these idealizations via de-idealization procedures. A more recent cluster of views, due to Potochnik (2017) and Knuttila & Morgan (2019), pushes back by arguing that these idealizations stand on their own and need no explicit de-idealization, and that de-idealization is too demanding, respectively. I’ll argue that this disagreement hinges on a strong philosopher’s construct of de-idealization, an idea that itself needs to be de-idealized. I explicate two weaker senses in which idealizations can be de-idealized.
Putting Pressure under Pressure: On the Status of the Classical Pressure in Relativity (draft available upon request!)
Much of the century-old debate surrounding the status of thermodynamics in relativity has centered on the search for a suitably relativistic temperature; recent work by Chua (2023) has suggested that the classical temperature concept – consilient as it is in classical settings – ‘falls apart’ in relativity. However, these discussions have still tended to assume an unproblematic Lorentz transformation for – specifically, the Lorentz invariance of – the pressure concept. Here I argue that, just like the classical temperature, the classical concept of pressure breaks down in relativistic settings. This situation suggests a new thermodynamic limit – a ‘rest frame limit’ – without which an unambiguous thermodynamic description of systems does not emerge. I end by briefly discussing how thermodynamics, in requiring preferred frames, bears on the idea of so-called symmetry-to-reality inferences.