My research primarily investigates the metaphysical and epistemological issues that arise from modern physics. Physical theories are often formulated in highly abstract mathematical terms, which tend to obscure their conceptual implications. The tools of philosophy are particularly helpful for understanding what physical theories say about our world. My current research spans four overlapping areas: (1) laws of nature, (2) time’s arrow, (3) philosophy of quantum mechanics, and (4) probability and decision theory. My long-term goal is to develop a comprehensive philosophy of science that brings these areas together in new ways. In addition to those interests, I am pursuing research in philosophy of mind and Chinese philosophy.
I have been developing a new account of laws of nature that vindicates the conviction that laws govern our world while remaining flexible enough to accommodate the variety of kinds of laws entertained in physics. In “Governing without a Fundamental Direction of Time: Minimal Primitivism about Laws of Nature” (Rethinking the Concept of Law of Nature, Springer 2022), Sheldon Goldstein and I propose this new account, called minimal primitivism (MinP), according to which laws of nature govern the world by constraining its physical possibilities. This view does not presume a fundamental direction of time or impose metaphysical restrictions on the forms of laws. In particular, it does not require fundamental laws to be dynamical laws. In "Algorithmic Randomness and Probabilistic Laws," Jeffrey A. Barrett and I develop a constraining notion of probabilistic laws.
In “Fundamental Nomic Vagueness” (The Philosophical Review, 2022), I introduce and characterize a new kind of vagueness—vagueness in the fundamental laws of nature. I suggest that it may be regarded as vagueness in the world. I turn to the Past Hypothesis, the low-entropy initial condition of the universe, as a case study. The paper was selected by The Philosopher's Annual as "one of the ten best articles in philosophy from 2022." A popular version of this article was published in the British science magazine New Scientist, and featured as the cover story in the magazine’s September 5th, 2020 issue.
Currently, I am writing a book entitled Laws of Physics(under contract with Cambridge University Press). I am also working on two new paper about laws. In “The Simplicity of Physical Laws,” I propose that both Humeans and non-Humeans should accept that simplicity is a fundamental epistemic guide for discovering and evaluating candidate physical laws. This principle of simplicity clarifies and solves several problems of nomic realism and simplicity. In “Strong Determinism” (Philosophers' Imprint, forthcoming) I investigate the possibility that the fundamental laws of physics uniquely determine the entire history of the universe, down to its exact initial condition. This notion of ‘strong determinim’ has implications for philosophical debates about explanation, causation, prediction, fundamental properties, free will, and modality. I also formulate an example of a realistic, simple, and strongly deterministic physical theory–the Everettian Wentaculus. A shorter essay on strong determinism, focusing on the Hartle-Hawking proposal, was published in Nature.
Life on the Edge
I am a member of the interdisciplinary project "Life on the Edge," led by physicists Jim Al-Khalili and Andrea Rocco at the University of Surrey, joined by collaborators at Bristol, Surrey, Oxford, UCLA, and Arizona State, and funded by a $3 million grant from the John Templeton Foundation. Here is the official project description: "In this project we will investigate the complex interrelationship between the nature of time and the distinct ways in which the passage of time and quantum physics manifest in inanimate objects compared to living organisms. Expanding the theoretical and philosophical frameworks used to understand the ‘arrow of time’ and reversibility, the project will encompass three theoretical investigations, an experimental approach using live cells, and a philosophical exploration of the deeper meanings of time." My focus will be on the relation of quantum ontology and the arrows of time in living systems.
Time's Arrow in a Quantum Universe ['The Wentaculus']
I have been working on a new project related to time's arrow in a quantum universe. The key idea is that the arrow of time in our universe is crucial for understanding the nature of quantum mechanics and vice versa. I propose that the "fundamental" quantum state of the universe is a special "mixed state," represented not by a wave function but a density matrix, selected by what I call the Initial Projection Hypothesis. I call the whole package 'the Wentaculus.' The idea was first presented in my 2021 BJPS paper, which won the Popper Prize.
I suggest that we should trace various philosophical puzzles of quantum mechanics back to their source--the wave function. First, I clarify how its mathematical representation relates to the physical world. In "An Intrinsic Account of Quantum Mechanics: Progress in Field's Nominalistic Program," I show that the wave function represents four intrinsic relations on physical space-time, uniquely up to certain symmetries. Since my intrinsic account dispenses with any reference to mathematical objects, it extends Field's nominalistic program to the quantum realm. In "Our Fundamental Physical Space: An Essay on the Metaphysics of the Wave Function" (JPhil, 2017), I argue against configuration space realism, the view that physical space-time is "emergent" from the high-dimensional configuration space that the wave function lives on. Emphasizing the roles of dynamics and symmetries, I show that physical space-time is more fundamental than the configuration space. In "Quantum Mechanics in a Time-Asymmetric Universe: On the Nature of the Initial Quantum State" (BJPS, 2018), I show that, by using the Past Hypothesis to pin down a simple and unique quantum state, we discover a new way of thinking about the relationship between the quantum state of the universe and the arrow of time. My proposal leads to a new class of quantum theories that dispense with certain objective probabilities and reconcile Humean supervenience with quantum entanglement. This paper is related to the first project.
Decision Theory and Infinite Values
I have been working, in collaboration with Daniel Rubio, on the foundations of decision theory and analyzing the paradoxes related to infinities such as Pascal’s Wager and the Pasadena Game (Nover and Hájek, 2004). In our paper “Surreal Decisions” (PPR, 2018), we propose a decision theory framed entirely in John Conway's (1974) surreal numbers. By using surreal numbers as the values of the utility function and the probability function, we show that many paradoxes of infinite values disappear in finite state spaces. In particular, dominance principles are no longer in conflict with expected utility theory. We are working on a second paper that extends surreal decision theory to the more advanced setting of infinite state spaces, such as the Pasadena Game. As a decision theory that systematically handles infinities and infinitesimals, our surreal theory has applications in value theory, population ethics, and philosophy of religion.
Metaphysics of Mental Qualities
I have another research project about metaphysics of quantities and philosophy of mind. Mental qualities (such as being painful and being conscious) are usually taken to be absolute and monadic. In my paper "Comparativism about the Mind: From Metaphysics of Quantities to the Nature of Mentality," I propose a new hypothesis about the nature of mental qualities: they are fundamentally comparative; for example, being more painful than is more fundamental than being painful. I call this the Comparative Mentality Hypothesis (CMH). CMH is motivated by comparativism about the physical as well as some theories about the mind-body problem. I use color qualities as the main example for CMH, and I provide an axiomatic foundation of color hues in terms of two comparative relations: cyclic-betweenness and cyclic-congruence. They turn out to have the same comparative structure as wave-function phases (Chen 2017a). I draw some consequences from CMH for reductionist physicalism and what David Chalmers (forthcoming) calls micro-idealism. In future work, I will apply CMH to other mental qualities and contrast it with comparativism about subjective probabilities.
I have two research projects in Chinese philosophy. The first one is at the intersection of classical Chinese philosophy and meta-ethics. In my paper “A Hybrid Voluntarist Interpretation of Xunzi,” I display tensions in the notions of xin (heart/mind), li (rituals), and dao (order) in the work of Xunzi, a prominent early Confucian philosopher, and I draw on Ruth Chang’s (2013a, 2013b) meta-ethical theory of hybrid voluntarism to help resolve these tensions. The second project is about issues related to the “Needham Question” about the history of science in China. I explore the connections between concepts of laws of nature with the concept of Dao in Chinese philosophy.