Grant: Discovery Grants Program - Individual

It was found in 1998 by studying distant supernovae that the expansion of the universe is accelerating. Most explanations for this shocking discovery fall into one of two classes: dark energy or modified gravity models. In the first, it is assumed that Einstein's theory of general relativity is valid and that a mysterious form of dark energy with exotic negative pressure permeates the universe. Observational data seem to require a form of dark energy ("phantom energy") so exotic that it may cause the universe to end its existence in a future Big Rip singularity (the end of time), with all bound objects (galaxies, planets, humans, atoms) being ripped apart by increasing gravitational forces. If phantom energy is fueling  cosmic acceleration, we probably have to abandon Einstein's theory in favour of scalar-tensor gravity, a generalization of relativity motivated by string/M theories, which attempt to unify gravity with the other three fundamental forces. The second class of models, modified gravity, does not require exotic dark energy but instead modifies Einstein's relativity with corrections that affect only large (cosmological) scales. My research explores both classes of models: trying to fully understand their dynamics, explain cosmic acceleration, developing models that are theoretically consistent and compatible with available experiments, studying their predictions  (e.g., will the universe accelerate forever? will it end in a Big Rip?), and related issues such as the production of gravitational waves, or the fate of black holes and wormholes. Goals include developing the correct theory of gravity (possibly, departures from Einstein gravity are already observed in the cosmic acceleration), finding out if dark energy really exists and, if so, its strange properties, understanding the early universe, obtaining information otherwise inaccessible on Earth on the physics at very high energies that have left an imprint in the cosmic microwave background and in the distribution of galaxies and galaxy clusters in the universe. Unveiling the correct theory of gravity would have tremendous implications for physics and human knowledge. Contributions to this goal would maintain or improve Canada's current position as the third or fourth contributor to research in cosmology worldwide.