Research/Areas of Interest:
Cosmic strings, gravitational waves, anthropic reasoning in cosmology,
energy conditions in general relativity.
Research:
My main area of research is the study of cosmic strings, in particular
their production of gravitational waves, which might enable us to
detect the cosmic string network, if it exists. Cosmic strings are
one of the potential sources of a stochastic background of
gravitational waves that (as of September 2020) may have been seen by
pulsar timing arrays. With my collaborators, I have developed a
large-scale simulation of cosmic strings, and we are the process of to
going from simulation results to predictions for the gravitational
wave background, with all effects included.
I also study gravitational waves and the possibilities of observing
them more generally. I am an associate member of NANOGrav (the North
American Nanohertz Observatory for Gravitational Waves), which
observes gravitational waves using precision timing of pulsars.
I work on issues of anthropic reasoning in cosmology and how to make
sense of the infinite multiverse produced by eternal inflation. I
study the structure of eternally inflating universes and also the
philosophy of how to get from a model of what actually exists
everywhere in the universe to an understanding of what we ourselves
should expect to observe.
I have worked for many years on the question of exotic phenomena such
as superluminal travel and time travel in general relativity. My
collaborators and I showed that, subject to certain conditions, a
minimally-coupled quantum scalar field obeys the "achronal averaged
null energy condition", which prohibits exotic spacetimes. I am
currently working on the interaction between eternal inflation and
energy conditions.