Speaker: Paul Steinhardt, Princeton University
 

A decade ago, the composition of the universe appeared to be a simple story: five per cent ordinary matter and ninety-five percent dark matter, where the latter most likely consists of weakly interacting massive particles. Today, growing evidence suggests that matter, both ordinary and dark combined, is but a minor player in the universe. Most of the energy consists of some ubiquitous dark energywith the remarkable property that it is gravitationally self-repulsive, causing the expansion of the universe to  accelerate outwards. Also, some evidence suggests that the dark matter itself  may have more complex properties than previously supposed.  This talk will discuss the evidence and some of the theoretical explanations that are being explored.