information in an image, Auger

I had long conversations with Rob Fergus (NYU) and Lang about the information content of an image. Dustin resolved some of my paradoxes, in particular he figured out that you can't say anything about how much information is in your image unless you know the distribution function over images! That distribution function is incredibly hard to describe, of course, since even for tiny images like Fergus's, it has a googol-cubed dimensions! Fergus's approach is to describe this function by sampling it, in some sense, but really what we have to do in our work is just approximate it in some sensible way.

In the afternoon, Jeff Allen (NYU) gave an excellent PhD candidacy exam talk in which he described how to reconstruct the physical properties of cosmic rays incident on the atmosphere from their fluorescence and ground-shower properties as measured by different Auger instruments. There are lots of puzzles in the reconstructions, and some of them will have mundane resolutions. There is an interesting possibility, however, that some will have extremely non-trivial resolutions.