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 thereafter by numerous electromagnetic observations of the event, from gamma rays to radio waves. LIGO recently completed its third observing run, with dozens more mergers detected. And in 2019, yet another groundbreaking observation when the Event Horizon Telescope captured the first image of the "shadow" of a black hole. 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. 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 can 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 relativistic 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.

We have support from Princeton University for operations through 2025, and recently completed new space on the fourth floor of Jadwin Hall adjacent to the Princeton Center for Theoretical Science (PCTS). This space includes offices for post-docs and visitors, a new meeting area, and a common space to bring together participating faculty and students. The Princeton Gravity Initiative further partners with the PCTS to host conferences and visitors. Whereas PCTS has excelled at uniting all areas of scientific inquiry, the PGI will be more focused on pushing forward gravity-related research programs already vigorously underway in the departments of Mathematics, Physics, and Astrophysics.