# About

In the century since the publication of Einstein's theory of general relativity, strongly curved spacetimes, from black holes to cosmological histories, have been the focus of intense study. Following LIGO's historic first detection of gravitational waves from colliding black holes in 2015, we now have a direct window of observation into events whose power briefly exceeds the combined power of all the stars in the known universe. Another historic first event occurred in 2017, when LIGO observed the merger of two neutron stars in gravitational waves, followed soon there after by numerous electromagnetic observations of the event, from gamma rays to radio waves. But strong gravity still harbors many mysteries, including quantum effects, dark energy, the origins of the Universe, and what happens inside black holes and neutron stars. LIGO is gearing up for its next observing run, expecting to see many more merger events. Soon we hope to have images from the Event Horizon Telescope of the enormous black hole at the center of our galaxy. Pulsar timing measurements are ongoing, and may soon reach a level of precision where a stochastic background of gravitational waves from supermassive black hole binaries could be detected. Cosmic microwave background polarization observatories are honing in on primordial gravitational waves created in the early universe.

Against the backdrop of these exciting observational advances, now is a key moment for mathematics, theoretical physics, and astrophysics to come together-in the tradition of past Princeton luminaries John Wheeler, Bob Dicke, and Howard Robertson-to push toward a deeper, interdisciplinary understanding of gravity. Princeton University's departments of Astrophysics, Mathematics and Physics have therefore banded together to form a new program called the *Princeton Gravity Initiative*, to explore the fundamentals of the force we call gravity.

Princeton's researchers have many independent strengths, including numerical relativity, rigorous mathematical analysis, quantum aspects of gravity, and accretion disk astrophysics. What was missing was an over-arching effort to bring these fields together so that key insights can be shared. The Princeton Gravity Initiative was launched to be that effort, and will focus on bringing a diverse group of young researchers to Princeton to collaborate with the faculty, cross-pollinate among disciplines, and grow into the next generation of leading scholars in general relativity and related fields.

The participating faculty are Mihalis Dafermos, Alex Ionescu, Sergiu Klainerman, Igor Rodnianski, and Yakov Shlapentokh-Rothman (Mathematics); Steve Gubser, Igor Klebanov, Paul Steinhardt, Frans Pretorius, and Herman Verlinde (Physics); and Adam Burrows, David Spergel, Anatoly Spitkovsky, and Jim Stone (Astrophysics). The first three Gravity Initiative Fellows are William Cook, Netta Engelhardt, and Martin Taylor. Several other Princeton faculty, postdocs and graduate students will also partake in the activities of the initiative (see the People page for the full list).

We have support from Princeton University for operations for six years, plus plans to establish new space on the fourth floor of Jadwin Hall adjacent to the Princeton Center for Theoretical Science (PCTS). This space will include offices for post-docs and visitors, a new meeting area, and a common space to bring together participating faculty and students. The anticipated completion of the new space is Fall 2019. The Gravity Initiative will further partner with the PCTS to host conferences and visitors. Whereas PCTS has excelled at uniting all areas of scientific inquiry, the Gravity Initiative will be more focused on pushing forward gravity-related research programs already vigorously under way in the departments of Mathematics, Physics and Astrophysics.