The Matter with Gravity

One hundred years ago this year, Albert Einstein unveiled a breathtaking new view of gravity. No longer was gravity even a force, as in Newton's old theory; instead, gravity's attraction was revealed to be essentially geometric, arising through the bending of the fabric of spacetime. For over thirty years, Einstein then tried, without success, to regard matter geometrically as well, so as to have a single unified formulation of both matter and gravity. In this project, we pursue Einstein's dream of unifying matter with gravity, but with a twist: instead of making matter more like gravity, we make gravity more like matter. From this perspective, the smooth fabric of spacetime emerges from some underlying "atoms of spacetime", roughly in the way that the smooth liquidness of water emerges from grainy underlying molecules of H2O. There have been hints from the theory of black holes that this might indeed be the right way of thinking about gravity. Thus our proposal confronts the big question "What is gravity?" and an even older question "What is the relation between space and time and substance?". This paradigm of emergent gravity, while appealing, has had few concrete successes to date. Here we will use it to try to derive a mysterious property of the universe, the so-called energy conditions, that otherwise have no explanation. The energy conditions are critical to Einstein's theory; they help to determine which of the countless possible spacetime geometries are unphysical (for example, those permitting time travel to the past). The deliverables will consist of five academic papers, six seminars, two conference talks, a public lecture and an op-ed. We will also organize a meeting of leading scientists. This project could provide a glimpse into the deepest shared origins of gravity and matter; the resulting scientific papers and conference would help to draw other scientists to the remarkable paradigm of gravity as emerging from the "atoms of spacetime".