Department of Physics and Astronomy Colloquia
Fall 2011 / Spring 2012

Gino Segre
University of Pennsylvania
Ordinary Geniuses: The Story of Two Physicists Who Changed Science

Born early in the 20th century, Max Delbruck and George Gamow were maverick physicists, each of them having as well a great sense of humor. The two lifelong friends went on to become pioneers in molecular biology and cosmology respectively. Their story illustrates some of the strengths and weaknesses a physicist might have entering a new field of science.

Robert Jaffe
MIT
Between Poets and Professionals: A ``Physics of Energy'' Course at MIT

New "physics for poets" courses on energy and the environment, requiring little or no science background, have sprouted up at colleges and universities across the country. At the other extreme are advanced courses on specialized subjects like photovoltaics, nuclear physics, or thermal fluids. My colleague, Washington Taylor, and I have aimed between these extremes, trying to teach the foundations of energy science to a broad but scientifically literate undergraduate audience. Our course, "The Physics of Energy", is open to all MIT students who have completed the first-year core of calculus, calculus-based physics, and chemistry. We address energy issues in a sophisticated and analytic way --- interweaving fundamental physics concepts like entropy, fluid dynamics, and quantum tunneling with applications of those principles to energy systems. The course has attracted students majoring in political science and management as well as in science and engineering. Although some aspects of our experience are unique to MIT, most of the challenges we faced would confront any physics department that tried to teach the foundations of energy science to engineers and scientists. I'll describe our motivation, the approach we have taken, where we feel we have succeeded and where challenges remain. Recently our course has been adopted as part of MIT's new "energy minor", which I'll describe as well.

Justin Khoury
University of Pennsylvania
Symmetries of the Early Universe

Our universe enjoys a lot of symmetry. On the largest scales, the universe is homogeneous and isotropic, consistent with a spatially-flat Friedmann-Robertson-Walker space-time. The density inhomogeneities in the early universe, which later give rise to galaxies and the large scale structure, are the simplest imaginable: their statistics are approximately scale invariant and well-described by a gaussian random field. In this talk, I will describe three broad classes of early universe theories that can account for these observations: single-field inflation, multi-field inflation and the recently-proposed pseudo-conformal universe. I will show that each class of models is associated with distinct symmetries, which imply subtle constraints on the form of the primordial density correlation functions through Ward identities.

Masao Sako
University of Pennsylvania
Cosmology with Supernovae

Distance measurements using explosions of white dwarf stars have played a central role in modern cosmology, leading to the remarkable discovery that the universe is presently going through an accelerated expansion. Despite more than a decade of extensive observational and theoretical efforts, the physical origin of this acceleration remains a complete mystery. Candidates include the existence of an unidentified source of a repulsive force by "dark energy" or the possible breakdown of general relativity on cosmological scales. I will discuss the observational evidence for cosmic acceleration and major observational advances that will be made in the near future.