I am interested in the interface between gravitation, cosmology, astro- and particle physics. These are developing fields where we do not yet know all the answers. They are places in which theoretical speculation used to run rampant, but is now increasingly checked by experiment and observation. And the questions could not be more important. Some recent investigations:

- The need for a new test of
**Equivalence Principle**, the foundation of General Relativity. This principle is violated in nearly all attempts to unify Einstein’s theory with the Standard Model, but only a space test at low temperatures (using at least three different test materials) can really begin to probe the theoretical parameter space. Such an experiment could also easily rule out inertial versions of MOND, the Modified Newtonian Dynamics alternative to dark matter. - Results from the
**Gravity Probe B**experiment and their implications for various theoretical approaches to unification. Many of these results can be understood in terms of gravito-electromagnetism, a formulation of Einstein’s theory for weak fields and low velocities that is closely analogous to Maxwell’s theory (see illustration at top of page). as a framework for unification. These might manifest themselves through variation of fundamental “constants” like rest mass, or through seemingly acausal effects in laboratory experiments. I have just published a new book on this subject (2018; cover at right. Reviewed by Phillip Helbig in__Extra dimensions__*The Observatory*)- A new way to visualize the interiors of
**spinning black holes**through mathematical quantities known as curvature invariants (see preprint or published paper) - New mechanisms for
**dark energy**that can successfully account for both cosmic acceleration at late times and cosmic inflation in the early universe. There is a mismatch of 122 orders of magnitude between the density of dark energy predicted by the Standard Model and that implied by observations based on Einstein’s theory, and many think that resolution of this issue will point the way toward unification. **Book on the scientific history**of dark energy with Helge Kragh (2014; cover at right. Reviewed by Simon Mitton in*The Observatory**The Journal for the History of Astronomy)*

Much of this research involves students. If you are an undergraduate student or potential high school intern, and interested in learning about subjects like the above, you are welcome to look at my list of ongoing opportunities for new research projects and talk to me, ideally in person.