As promised before my extended season-of-indulgence break, I thought I'd report on my day at the 8th Northeast String Cosmology Meeting, organized by the Institute for Strings, Cosmology and Astroparticle Physics at Columbia University, and held at the The New York Academy of Sciences in their new home in the rebuilt 7 World Trade Center. This meeting is held once per semester, and up until now was held rather informally at Columbia. This time, for a variety of reasons, some due to scheduling conflicts, and some to do with an increased profile of the New York Academy of Sciences, it was held in this swanky new location, with a breathtaking view of Manhattan. The format is to have four invited speakers so that, as well as my own talk, Nathan Seiberg, Justin Khoury and Raphael Bousso were also speaking. Seiberg's talk was a nice and interesting discussion of how one might break supersymmetry by living in a metastable vacuum state, and the implications that might have. While he didn't discuss the cosmology of such a scenario, it did seem to me that there might be some interesting features, and I should definitely go and read his paper with Intriligator and Shih sometime in the near future. Justin, as usual, did a very nice job of describing his very recent paper on fading gravity. Inspired by a specific proposal of Sundrum (the fat graviton scenario), Justin has studied general phenomenological properties of models in which gravity shuts off at short distances, including the discovery of self-inflating solutions predicting a blue tilt for the tensor spectrum. After a lovely lunch overlooking downtown Manhattan, it was time for my talk. I spoke about the challenges of constructing a consistent infrared modification of gravity yielding late-time cosmic acceleration, provided some specific examples and showed how they run into problems with solar system tests and/or are plagued by ghosts. I then described work that Sean and I have done (with his graduate student Ignacy Sawicki and my graduate student Alessandra Silvestri) on Modified Source gravity, finishing up with a discussion of how structure formation observations may help distinguish between different models. Raphael was the final speaker, with the provocative title Predictions in the Landscape. Based on his recent paper, the topic was a suggestion that the way to assign probabilities in a theory with multiple metastable vacua (like the landscape) is to construct a measure based only on a causally connected region. One thing I loved about this meeting was the large number of people who I know from various nearby and not so nearby institutions who attended. For some reason I hadn't expected to see so many of them and it made for a fascinating day. It was also nice to see so many friends. That I got to spend the rest of the weekend in New York with Sara and a couple of friends who met us there was a wonderful bonus. This seems like as good a place as any to thank Brian Greene, Joel Erickson and Sash Sarangi for such a stimulating and fun day.
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