Institute for Advanced Study Astrophysics Seminar

Inflation is a (deceptively) simple idea in cosmology which ties directly to observational data on the one hand, and to difficult problems in formulating quantum gravity on the other hand. The mechanism behind inflation is sensitive to very high-energy physics, which motivates inflationary model building within an ultraviolet-complete theory of gravity (such as string theory). I will review mechanisms for inflation arising from the internal structure of string theory which produce distinctive signatures in gravity waves and/or non-Gaussian corrections to the power spectrum. Meanwhile, on the (even) more theoretical side of the subject, it is not clear how to formulate inflationary cosmology since it leads to causally disconnected regions of spacetime. One clue as to the relevant degrees of freedom is that cosmological horizons carry an entropy which begs for a microscopic interpretation. If time permits I'll mention new results on a semi-`holographic' construction of inflating (de Sitter) solutions in string theory, aimed at a microscopic interpretation of the Gibbons-Hawking entropy associated with cosmological horizons.