Cosmology is different from other areas of the physical sciences, both in its subject matter – the universe as a whole – and in the tools we use to study it. Standard experimental and theoretical methods used throughout the rest of the physical sciences have little traction in cosmology, where we have only one universe to study and many of the features of greatest interest are removed from us in space and time. These methodological difficulties, coupled with the profound importance of understanding the history and structure of the universe, make cosmology an urgent subject for philosophical research.
Chris Smeenk (Rotman Institute of Philosophy, Western University)
James Owen Weatherall (University of California, Irvine)
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.
- Statement of Significance:
The desire to understand the universe around us, and our place in it, is a profound part of the human experience. And today, thanks to a century of work in relativistic cosmology, we have a clearer picture of the origin and evolution of the universe than ever before. For the first time, we have something that deserves to be called a “Standard Model” of cosmology, rivaling the Standard Model of particle physics in its explanatory range. Cosmologists have celebrated these successes – but they have also been cautious. While we appear to have developed successful models of our cosmological history, doing so has required cosmologists to bend – and in some cases, reinvent – the rules of accepted scientific practice, prompting a startlingly open debate about the methodology of cosmology among working cosmologists.
For many of these physicists, explicit methodological debate is unfamiliar territory. This creates an unusual opportunity for meaningful collaboration between physicists and philosophers. Even as some physicists, such as Stephen Hawking and Lawrence Krauss, claim that philosophy is dead, others are beginning to see ways in which philosophy is not only useful, but essential to their own work. As science moves into new territory, so too must our conception of what constitutes reliable inference, sound methodology, and acceptable evidence – all of which have been central to the philosophy of science for decades. Renowned Princeton cosmologist Paul Steinhardt summed it up in a recent interview with Aeon magazine: “I wish the philosophers would get involved.”
Of course, the philosophers have been involved. Philosophy of cosmology does not have a focused agenda like other areas, such as foundations of quantum theory, but it has recently attracted much more interest from philosophers and cosmologists. The Templeton Foundation funded two previous projects in Philosophy of Cosmology that have opened up various lines of research. These previous projects focused in part on the ramifications of cosmology for issues already of interest in foundations of physics (the past hypothesis; solutions to the measurement problem) and in the metaphysics of physics (the status of laws of nature). There is value in seeing cosmology in light of these problems: after all, a full understanding of structure formation in the early universe demands a story about the quantum-to-classical transition, and cosmology raises intriguing challenges for metaphysics of science. But it is our view that these other projects have not fully explored the philosophical issues arising within cosmology itself – issues concerning the epistemology of multiverse theories, the criterion of “falsifiability” for sound theorizing, the status of anthropic reasoning, and the evidentiary power of simulations, among many others.
In our view, part of what makes cosmology so rich for philosophical inquiry is its wealth of problems that are apparently unique, at least within physics. A focus on traditional problems in philosophy of physics misses this richness. For this reason, the project we describe here takes a different tack, intended to complement the previous projects. Rather than look to philosophy of physics specifically, we aim to bring to bear the insights of decades of work in general philosophy of science on evidence, theory choice, and scientific methodology, to make progress on issues of urgent interest to working cosmologists.
For these reasons, we expect this project to have a different kind of significance for cosmological practice than some other work in philosophy of cosmology. It will, we hope, help to isolate the distinctive features of cosmology that give rise to the need for novel methodological innovation in the first place. It will also present cosmologists with new tools for thinking about the evidential situation they face. One of the striking things about the ongoing methodological debates in cosmology is that they rely on distinctions and criteria – science and pseudoscience; falsifiability – that philosophers of science have long argued never adequately captured successful scientific practice. Instead, most philosophers of science today accept some variety of belief-revision model of knowledge, according to which theories (or models) have more or less support, given the available evidence, but no evidence should be taken as straightforwardly confirmatory or falsifying. This picture of the relation between evidence and belief seems far better suited to the situation in cosmology than the one cosmologists appear to have inherited from a previous generation of physicists. And if accepted by cosmologists, it could radically restructure current disputes about the state of the field.
- Central Questions:
The project will address the following Big Questions inspired by the startling progress in cosmology over the last 50 years.
- Is it possible to discover and justify new fundamental laws in cosmology?
The Soviet cosmologist Zel’dovich once called the early universe “the poor man’s accelerator,” because one can study effects of particle physics theories using telescopes to observe the early universe, rather than building accelerators. Yet there are important contrasts between probing new ideas with well-designed experiments, and attempting to discern their impact on past evolution. In other words, what kind of science is cosmology? And what can be achieved in that kind of science?
- Does cosmology require new rules for testing theories?
Sometimes new scientific theories prompt new theories of science – that is, new ideas about how science works. Cosmologists have recently advocated controversial new ways to test theories. The impetus for these proposals comes from considering multiverse theories inspired by inflationary cosmology and string theory. To test competing multiverse theories, they argue, one needs to calculate what a “typical observer” should expect to see according to each theory, and compare these results to observations. Yet there is not a standard account of how this is supposed to work, and it is also not clear whether this proposal is compatible with more conventional accounts of how to test theories. This proposal will address the question of whether “anthropic reasoning,” as it is often described, provides a reasonable account of how to test theories. We will also consider alternative accounts of methodology that do not rely on anthropic predictions, inspired by comparisons between cosmology and historical sciences.
- What is the status of spacetime concepts in cosmology?
Cosmology depends on Einstein’s general relativity and its account of spacetime geometry. The status of the assumptions regarding spacetime geometry can be challenged in two different ways. First, there are a variety of properties typically assumed to hold for “reasonable” spacetimes. One challenge to these assumptions comes purely at the classical level, in assessing the justification for these assumptions. A distinct challenge concerns the fate of spacetime in new theories of quantum gravity. In what sense can spacetime itself “emerge” from a theory that does not introduce spacetime at a fundamental level?
III. Project Activities:
The core goal is to develop a new sub-discipline in philosophy of science. Part of our strategy for doing so is to host three workshops, bringing together different permutations of scientists and philosophers under the project’s core themes. These workshops will allow us to identify the philosophical issues of greatest interest to working cosmologists, giving us a clearer target for future work. We will also train the junior scholars who will pursue these topics. We will fund multiple graduate students, and a postdoctoral fellow, at UC Irvine and the University of Western Ontario, two of the top-ranked PhD programs in philosophy of physics and philosophy of science in the world. These funds will incentivize younger researchers to take an active role in developing the field, and to receive the training necessary to make long-term contributions and to support a self-sustaining literature oriented towards the needs of the science.
“The Cosmos As Involving Local Laws and Inconceivable without Them”, with Yann Benétreau-Dupin. The Monist (2017) 100 (3): 357-372.
“Philosophy of Cosmology,” with George Ellis. Stanford Encyclopedia of Philosophy.
“Testing Inflation,” in Philosophy of Cosmology, edited by K. Chamcham, J. D. Barrow, J. Silk and S. Saunders, Cambridge: Cambridge University Press (2017), pp. 206-227.
“Philosophy of the Physical Sciences,” with Carl Hoefer. In Oxford Handbook of the Philosophy of Science, ed. by Paul Humphreys. Oxford: Oxford University Press (published online 2015; in print Sept. 2016).
Benétreau-Dupin, Yann. “Blurring Out Cosmic Puzzles,” Philosophy of Science (PSA 2014), forthcoming 2015 (preprint)
“Einstein’s Role in the Creation of Relativistic Cosmology.” In The Cambridge Companion to Einstein, edited by M. Janssen and C. Lehner. Cambridge University Press (2014), pp. 228-269.
“Predictability crisis in early universe cosmology,” Studies in the History and Philosophy of Modern Physics. (2014): 122-133, available online.)
“Time in Cosmology,” in The Blackwell Companion to the Philosophy of Time, ed. by A. Bardon and H. Dyke. (preprint)
“Shifting Status of the Expanding Universe Models,” Thinking about Space and Time: 100 Years of Applying and Interpreting General Relativity, Bern, Switzerland (September 2017).
“Underdetermination in the Early Universe,” Probing the spacetime fabric: from concepts to phenomenology conference in Trieste, Italy (July 2017).
“Some Reflections on the Structure of Cosmological Knowledge,” invited speaker at The Philosophy of Howard Stein, University of Chicago (June 2017).
“Explaining the Initial State,” Foundations of Cosmology Workshop, University of Michigan (April 2017).
“Explaining the Origin of the Universe,” Invited Symposium: Philosophy of Physics and Cosmology in Practice, APA Pacific Division Meeting in Seattle, WA (April 2017).
“Challenges to Primordial Cosmology,” Methodology and Epistemology in Cosmology conference, UC Irvine, Irvine, CA (February 2017).
“Gaining Access to the Early Universe,” Philosophy of Science conference at Inter-University Centre, Dubrovnik (April 2015), LMU Munich (Dec. 2015), Stanford History and Philosophy of Science Colloquium (March 2016).
Benétreau-Dupin, Yann. “Blurring Out Cosmic Puzzles,” Imprecise Probabilities in Statistics and Philosophy workshop, MCMP, June 2014, and PSA 2014
“Predictions in Eternal Inflation,” invited speaker at the Rutgers Workshop on Philosophy of Cosmology. Rutgers, New Brunswick NJ (April 2014).
Benétreau-Dupin, Yann. “Cosmic Surprise, Anthropic Reasoning and Bayesian Analysis,” Foundations of Physics 2013, MCMP, July 2013
Benétreau-Dupin, Yann. “Methodological Implications of the Uniqueness of the Universe for Modern Cosmology,” CSHPS 2012 (abstract)
“Bayesian Anthropics” and “Predictions in Eternal Inflation,” Oxford Workshop: Anthropics, Selection Effects, and Fine-Tuning in Cosmology.
Conferences and Workshops:
UWO Philosophy of Cosmology Workshop