My research is focused mainly on questions of whether and how physics might amount to a fundamental and universal account of the entirety of nature. I have a deep and long-standing interest in the foundations of quantum theory—and (in particular) in the quantum-mechanical measurement problem—precisely because that is the point at which the whole project of physics has often been declared to have reached its ultimate limits, precisely (that is) because that is the point at which the aspirations of physics to amount to a complete account of the world have often been declared to decisively and irreparably break down. In recent years, I have also been thinking a great deal about the foundations of statistical mechanics, and the meaning of chance, and the arrows of time. This work has exposed very fundamental and surprisingly intimate connections between (on the one hand) the second law of thermodynamics, and the fact that we have a very different sort of epistemic access to the past than we do to the future, and the fact that by acting now we can affect the future but not the past, and (on the other) the large-scale structure and origins of the universe.
A basic theme in the research I'm likely to be involved in during the next few years is the indispensable role of taking ontology seriously when confronting issues in the foundations of quantum mechanics, especially cosmological issues. I would like to explore the status of the wave function of the universe in our quantum world. My feeling is that the most promising possibility is that this wave function, while objective, is not a concrete physical reality but rather a compact representation of the law governing the behavior of something else, the primitive ontology. The latter is given by objects and structures in space-time—what Bell called local beables—with which quantum theory should be regarded as fundamentally concerned. It is through the behavior of the primitive ontology, governed by the wave function of the universe, that quantum theory manages to make any experimental predictions at all, and to explain the things that physics is intended to explain.
My area of research is superstring theory, a theory that purports to give us a quantum theory of gravity as well as a unified theory of all forces and all matter. As such, superstring theory has the potential to realize Einstein's long sought dream of a single, all encompassing, theory of the universe. One of the strangest features of superstring theory is that it requires the universe to have more than three spatial dimensions. Much of my research has focused on the physical implications and mathematical properties of these extra dimensions --- studies that collectively go under the heading "quantum geometry."
I will be working on developing the Humean account of fundamental laws and chances that I have written on in the last few years and working out the details of accounts of time’s arrows in terms of statistical mechanics. I am also interested in exploring recent attempts to explain the very low entropy condition at the time of the Big Bang and the questions these attempts raise about the nature of explanation. I would also like to find out why anything exists at all.
There are several issues in relating to cosmology that I would like to pursue in connection with this project. One concerns the physical basis for the inflationary behavior of the universe that has motivated the reintroduction of a cosmological constant into the Einstein Field Equation. Another project, somewhat related to the first, is the construction of discrete models of geometry of the universe that can be coarse-grained to yield recognizably Relativistic space-times. This is an application of the new approach to topology that I have been developing for the past few years. One simple toy model that I have been investigating yields an exponentially inflating three-dimensional space-time, and the inflation can be traced to rather basic features of the rules for constructing the discrete geometry. I would like to investigate how both the supposed exponential inflation immediately after the Big Bang and the more gentle inflation now being observed might be incorporated into such a model. I hope that this might illustrate how a fundamentally discrete geometry might shed light on cosmological structure.
My interest lies in exploring computer simulations as extremely potent tools that share some similarities with experiments, theory and models, but are an independent epistemic tool. In fact, cosmological N-body simulations have played a very significant role in the establishment and acceptance of the current paradigm that best describes the growth and evolution of structure formation in the Universe: the LCDM (Lambda Cold Dark Matter) concordance model. By enabling detailed comparisons of theoretical model predictions with observations, simulations have not only refined and developed pre-existing theoretical models but have in fact engendered a new way to create and represent models. What is salient about this novel way to create viable models is that the validation and verification of a given model is clearly articulated, enabling clear discrimination between competing theories. I plan to study in detail the evolution of simulations and the transformations that it produced in tandem with growing observational data on the nature of cosmological theories.
I am working on the formation and evolution of galaxies and the nature of the dark matter that makes up most of the matter in the universe. After working on particle physics and writing papers that helped to create the Standard Model, I began working in cosmology in the late 1970s. With Heinz Pagels, I was the first to propose that a natural candidate for the dark matter is the lightest supersymmetric particle. I am one of the principal originators and developers of the theory of Cold Dark Matter, which has become the basis for the standard modern picture of structure formation in the universe. I am currently using supercomputers to simulate and visualize the evolution of the universe and the formation of galaxies under various assumptions, and comparing the predictions of these theories to the latest observational data. I am now the director of the University of California High-Performance Astro-Cpomuter Center. I am also working on the nature of dark matter, the formation and evolution of galaxies, and on high energy gamma ray cosmology. I will continue to work on these projects and am enthusiastic about the prospect of collaborating with philosophers on issues in philosophy of cosmology. Some of these issues are discussed in two popular books I co-authored with Nancy Ellen Abrams—The View from the Center of the Universe (Penguin/Riverhead, 2006) and The New Universe and the Human Future (Yale University Press, 2011).
Some of my planned research projects include: Jointly with Shelly Goldstein and others, analysis of cosmological scenarios in which every conceivable history passes through some low-entropy state at some time. How can the known quantum theories without observers (Bohmian mechanics, "GRW" theory of spontaneous wave function collapse, many-worlds) be transferred to curved space-time? Towards a precise formulation (and, if possible, derivation) of the second law of thermodynamics in the framework of quantum mechanics, analogous to Boltzmann's work in the framework of classical mechanics. Time evolution of quantum wave functions near space-time singularities. When gluing two space-time manifolds together at their singularities, does the Schrodinger-Dirac time evolution extend mathematically across the singular surface? Can one "survive a space-time singularity"?
I will be working on the question whether the universe shows any evidence of having been “fine-tuned” so as to allow for the existence of complex, interesting creatures like human beings. The apparent need for a teleological explanation behind the precise settings of fundamental constants and initial conditions might be just an appearance if our universe is part of a certain kind of multiverse. Fine-tuning arguments have been thought to support, not theism alone, but the disjunction of theism with a multiverse hypothesis. John Hawthorne, David Manley, and Robin Collins have claimed that the multiverse side of this disjunction is not nearly so well-supported, by the appearance of fine-tuning, as the theism side; and that is a question I hope to get to the bottom of. The result will be a chapter in a book on the philosophy of religion.