Presented by: Cliff Burgess, Perimeter Institute and MacMaster University

Abstract: 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. Amongst the surprises is 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 play a useful role in understanding puzzles with cosmology and black holes.

Host: Shanta DeAlwis

Coffee, tea, and cookies will be available starting at 3:45 p.m., in DUAN G1B31.