The View of the Universe from the South Side of Chicago

This last term I taught Introduction to Cosmology, a course for graduate students at the University of Chicago (although some undergrads typically do take it). While I have been known to pass myself off as a professional cosmologist, I've never found it a particularly easy course to teach. The straightforward reason is that it's a big universe out there, and not much time to cover it. The UofC is on a quarter system, so a term is only ten weeks of classes; this makes it hard to squeeze in as much material as you would be able to in an ordinary semester. More importantly, though, cosmology is a mess. Unlike most other subjects that would have a course devoted to them, there is no sense in which cosmology is a single logical structure that is built up from a small number of axioms. To discuss various crucial topics, you need to bring in general relativity, thermodynamics, particle physics, astrophysics, and occasionally the kitchen sink. In particular, neither GR nor particle physics are prerequisites for taking the course, so the basics of those subjects need to be covered when necessary. A substantial fraction of contemporary cosmology is devoted to investigating structure formation and the cosmic microwave background. To do those subjects any justice requires not only the basics of general relativity, but a pretty well-grounded understanding of relativistic perturbation theory, which is an intricate and subtle discipline all its own. So the prospective cosmology instructor has a choice: go whole-hog in doing structure formation and perturbation theory, skipping past many of the fun topics in early-universe cosmology, or do the converse, putting some effort into inflation and relic abundances and nucleosynthesis while waving hands briefly about large-scale structure and the CMB. Since there is a separate cosmology course taught in the Astronomy department, which inevitably concentrates on structure formation and the CMB, I chose the latter route. We covered the basics of general relativity (enough to derive the Friedmann equation for the expansion of the universe) and particle physics (enough to understand the basics of cross-sections and calculate relic abundances). Hopefully, the students who don't decide to become full-time working cosmologists will nonetheless, ten or twenty years down the line, recall the basic ideas of how to calculate the density of a dark matter candidate or why primordial nucleosynthesis provides such strong constraints on the physics of the early universe. There were problem sets every week, but no final exam. Instead, the students each wrote a final paper, and the good news is that you get to read them. The final papers have been put on a web page (as pdf files), and you could do much worse by way of reviewing the hot topics in current cosmology research than to read through these papers. (The indended audience for the papers was "people who have just taken this course," so they do tend to get a little technical.) In the past I've asked each student to pick a somewhat narrow topic and do a little review on it. This year, as an experiment, I instead asked them to find one specific research paper that had appeared in the past year or so, and write an overview of it that explained the main results as well as some of the background. Topics include: