Dr. Cliff Burgess McMaster University Email: cliffmacpi@gmail.com Speaker webpage: physics.mcmaster.ca/~cburgess/cburgess/

Thinking Effectively About Gravity (the view from below)

We live at a time of contradictory messages about how successfully we understand gravity. General Relativity seems to work well in the Earth’s immediate neighbourhood, but arguments abound that it needs modification at very small and/or very large distances. This talk tries to put this discussion into the broader context of similar situations in other areas of physics, and summarizes some of the lessons which our good understanding of gravity in the solar system and elsewhere has for proponents for its modification over very long and very short distances. The main message is mixed: On one hand short-distance quantum effects are notoriously difficult to control in gravity and cosmology seems to like features (like light scalars and small vacuum energies) that are not generic to the long-wavelength limit of fundamental theories. These are crucial clues that would be silly to ignore. On the other hand, General Relativity successfully passes many stringent new observational tests and also seems to be almost unique in its ability to reconcile quantum effects with gravity on longer distances without being inconsistent. Neither of these seems to offer much scope for modification. I try to organize what the successes of GR might be telling us, and provide a score-card about it says about the various alternatives that have been proposed.

I was born in Manitoba and was raised in various places around Western Canada, Ontario and Europe. I received my B.Sc. in a co-op programme, with a joint honours in Physics and Applied Math from the University of Waterloo. I did my doctoral work in Theoretical Particle Physics at the University of Texas in Austin under the supervision of Steven Weinberg. After doing a short postdoctoral stint at the Institute for Advanced Study in Princeton, in 1987 I joined the faculty at McGill University, where I was made James McGill Professor in 2003. I am presently a professor with McMaster University’s department of Physics and Astronomy and am an Associate Faculty Member at Perimeter Institute for Theoretical Physics. I have spent sabbatical years with the Institute for Advanced Study in Princeton as well as the University of Neuchatel and CERN in Switzerland. I was a Killam Fellow from 2005 – 2007 and elected a fellow of the Royal Society of Canada in 2008. I received the Canadian Association of Physicists/Centre de Recherches Mathematiques (CAP-CRM) prize for theoretical physics in 2010, and a Buchalter Cosmology Prize in 2016 and again in 2017.