Special Physics Colloquium

Dr. Mark Hertzberg, MIT

"The Accelerating Universe"

3:00pm, RLM 11.204

Coffee and cookies at 2:45pm.

Abstract: In this colloquium I discuss various aspects of an accelerating universe. This includes both early universe inflation and late time cosmic acceleration. I utilize the basic method of effective field theory, wherein much of the physics can be learnt by studying the system at sufficiently large scales compared to some microscopic scale. I begin by reviewing the profound consequences of quantum mechanics and special relativity, which organizes particles into half-integer spin from 0 to 2. The spin 2 particle uniquely leads to general relativity at large distances, while the spin 0 particle allows for a new phase of matter to occur, namely inflation, under appropriate conditions with vacuum energy. I discuss some difficulties to embed these accelerating phases into string theory and other microscopic constructions. On the other hand, I discuss the theoretical problems that emerge when one tries to replace these theories involving vacuum energy by modifying general relativity at large distances. I discuss the observational evidence that inflation occurred and that the late time acceleration arises purely from vacuum energy. To this end, I present an effective fluid description of our universe, discuss connections to particle physics, and I discuss the implications.