machine learning, CMB spectrum

In an informal seminar in the morning, Rashid Sunyaev (MPA) finally explained to me clearly why the CMB does not show Lyman, Balmer, Paschen, and so on recombination lines: The answer is that the baryon-to-photon ratio is so enormous that recombination contributes only a minute fraction of all photons. He showed nonetheless that it might be visible in the future by proposed PIXIE.

Prior to that talk I gave the last of our stats school lectures, this one on machine learning. I described some of the popular goals and methods in machine learning and connected them to physical science problems. I gave strong advice, which was mainly to avoid large classes of algorithms. In the afternoon, Shirley Ho (CMU) told us about a use of machine learning to take a few good simulations and lots of bad ones and build lots of (pretty) good ones at low cost.

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