We live at a time of contradictory messages about how successfully we understand gravity. General Relativity seems to work very 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 has for proponents for its modification over very long and very short distances. The main message is that effective theories (in the technical sense of effective) provide the natural (and arguably only known) precise language for framing proposals. Its framework is also useful, inasmuch as it makes some modifications seem more plausible than others, though there are also some surprises including about where the best places are to seek deviations from GR. Amongst the surprises is also evidence that in some ways gravity behaves more like condensed matter physics or optics than particle physics, raising the possibility that tools from these areas may be useful for understanding cosmology and black holes.
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.