Grant: Discovery Grants Program - Individual

Einstein's theory of gravity, general relativity, is very successful but it has shortcomings. Deviations from it are by no means excluded or tested everywhere. In spite of an apparent phenomenological success, the standard model of cosmology based on general relativity is spectacularly incomplete and unsatisfactory. First, there are severe discrepancies between measurements of the Hubble constant (which determines the age of the universe and the distances in it) at early and late times. Second, the nature of the fundamental ingredients of standard cosmology, i.e., dark energy, dark matter, and the field driving early universe inflation, remains a mystery together with spacetime singularities. Moreover, all attempts to reconcile general relativity with quantum physics introduce deviations from Einstein gravity. All this leads to study alternatives to general relativity. It is not even known whether gravity is fundamental or an emergent phenomenon like water, a liquid made of fundamental microscopic molecules but described by macroscopic average quantities. I am developing a formalism in which non-Einsteinian gravity emerges as a high temperature state of a fluid, while general relativity is a state of equilibrium at zero temperature. This idea has been around for sixteen years but no progress was made in identifying the ``temperature of gravity'' or describing its relaxation towards equilibrium. In the past year I broke new ground, finding a description of non-Einsteinian gravity as a viscous fluid (like maple syrup) and identifying the missing ``temperature of gravity''. I am excited to develop this physics in full and to examine many gravitational phenomena to establish when, how, and why gravity ``cools'' to general relativity or departs from it. This proposal will pose and answer fundamental and technical questions about gravity, cosmology, black holes, and spacetime singularities and will develop a thermal view of gravity, searching for new phenomena in various contexts and understanding more deeply cosmology and black holes. Perhaps there are even phenomena like the ``freezing'' or ``melting'' of gravity, like water turning into ice and vice-versa. I will explore when, how, and why gravity is ``hot'', i.e., departs from general relativity, which seems to happen near spacetime singularities (such as at the Big Bang or at a black hole centre). It is a little miracle that this fluid-like description of gravity works, but it does. This proposal, like most basic research, is unlikely to produce immediate applications but will help us learn about nature at its most fundamental level, which is inspiring. Changing our understanding of gravity would change the way we understand the universe and the objects in it. In the long run, all new fundamental descriptions of the four known forces (Maxwell's electromagnetism, general relativity, and quantum and nuclear physics) have always generated enormous fallouts changing our lives.