Chris Smeenk

New Directions in Philosophy of Cosmology 

Physical cosmology has enjoyed decades of progress, leading to a new understanding of the cosmos and our place in it. But this success comes with new puzzles. Cosmologists seek to understand events that are far removed from us. Moreover, in many cases they study historical episodes that are apparently unique — such as the origin of the universe — and which cannot be studied experimentally. To overcome these challenges, cosmologists have often revisited basic questions concerning what constitutes an acceptable scientific theory, what sorts of explanatory demands a theory of cosmology can meet, and how to understand confirmation in this context. Their answers to these — essentially philosophical — questions have shaped the character of cosmological theory.

The principal goal of this project is to articulate and scrutinize the philosophical commitments behind cosmology’s Standard Model. With the support of a planning grant, we have conducted a landscape review of the field to identify the most significant open questions. One part of the project will present what we take to be the “philosophy of science” underlying cosmological practice, reflecting on and extending the earlier work we have reviewed. The second part of the project will dive more deeply into two pressing conceptual issues, which we identified in workshops with cosmologists supported by the planning grant: (1) the epistemological significance of the crucial role now played by simulations in linking cosmological theory with observations; and (2) the status of the large-scale structure of the universe in light of suggestions from quantum gravity that characteristic features of general relativity, such as singularities, may not persist into future theories.

In addition to this research component, the project includes outreach and capacity-building activities. It will also provide substantial training opportunities at the pre-doctoral, post-doctoral, and established researcher levels.

I led this project as co-PI with Jim Weatherall, and collaborators James Bullock and Robert Brandenberger, with funding from the John Templeton Foundation (through grant 61048). See the project website for more information on the activities supported through the grant and outputs.

Structure of Effective Theories 

A central aim of philosophy of science is to characterize the nature, scope, and limits of scientific knowledge. To pursue that aim philosophers must clarify how theories represent the world and guide scientific practice. This project will develop and defend a novel account of scientific knowledge inspired by the “effective field theory” (EFT) view in physics. This account of the structure of theories contrasts sharply with conventional philosophical views, and provides the resources needed to reframe philosophical debates fruitfully.

There are two main objectives for the project. First, I aim to develop this EFT inspired account of theories as a general template for understanding the structure of theories, and their role in inquiry, both within physics and in science more generally. This work will be relevant to philosophers of science, as well as epistemologists and metaphysicians. Philosophical accounts of the structure of theories developed in the mid-20th century, largely inspired by physics, have cast a long shadow in philosophy of science. These accounts do not even capture essential aspects of how theories function in physics, as this project aims to show, so there is little reason to rely upon them in assessing other areas of science. This faulty view of the structure of theories has generated challenges, such as the difficulty of reconciling two conflicting lines of thought regarding the nature of scientific knowledge. On the one hand, new discoveries may overturn what we thought we knew; on the other hand, science has apparently achieved durable results. The project will culminate with a monograph that shows how the EFT view responds to this challenge.

Second, the EFT view will be developed and tested by examining case studies in the foundations of physics. These will focus on the technical sense of EFTs, developed in quantum field theory, and will critically highlight the limitations of the EFT view, with an aim to clarify the qualitative features of the framework that can be used to develop a new account of theories. Determining which features fail to generalize will help to decide which features can form the core of the general view. These case studies will also contribute to foundational debates in physics regarding the viability of EFT as a framework for quantum gravity and cosmology.

The project will pursue both objectives in tandem, starting with a series of collaborative papers on the distinctive features of EFTs, their limitations within the context of gravitational physics, and their relation to successive approximations and measurement theory. To begin, there are several features of EFTs that make for appealing contrast with traditional views in the philosophy of science. First, the EFT view treats theories as inherently related to other theories in a large, structured theory space of alternatives that bear specific formal relationships to one another. Second, EFTs contain explicit reference to a limited domain of phenomena to which they apply. Finally, the structure of the theory space provides resources for quantifying and limiting the impact of physics from outside the proper domain of an EFT. The EFT view both acknowledges our ignorance and delimits its impact on the current state of knowledge. These features form the basis for a general account of theory structure based on applied mathematics and notions of approximation, rather than formal logic. Once further features of such a view are fully developed, I will write a monograph presenting the new account of scientific theories, aimed at philosophers of science.

The project is being pursued in collaboration with Adam Koberinski, Jim Weatherall, and Francesca Vidotto.

Seventeenth Century Natural Philosophy 

My main interests in seventeenth century natural philosophy concern how sensory experience contributes to knowledge of nature, and the role of mathematics in enabling this contribution. I take Newton as introducing a particularly sophisticated and innovative answer to this question, in the form of a kind of quantitative empiricism. The theoretical framework of the Principia Mathematica makes it possible to take aspects of sense experience as measurements of fundamental quantities, such as mass. For example, the length of a particular pendulum measures the surface gravity in the appropriate circumstances. Although “gravity” may be a qualitative feature of ordinary experience, the precise quantitative measure of it is not directly accessible. The contribution sensory experience makes is necessarily theory-mediated, where in this case the relevant theory accounts for the connection between the length of the pendulum bob and the surface gravity. Furthermore, Newton does not, contra contemporaries such as Locke, require that the “fundamental” properties characterizing bodies are manifested as sensible qualities.

My work in this area has focused primarily on detailed assessment of Newton’s methodology, as it is reflected in different aspects of his mathematical physics. I have benefitted from working in collaboration with Zvi Biener, Eric Schliesser, and George E. Smith.