No. No. Not THAT controversy. I just got back from a meeting at the insanely cool Carnegie Observatory in Pasadena, California (Hubble's old digs) with Wendy Parker, Paul Humphreys, James Ladyman, and many extremely interesting and engaging astronomers. (Barry Madore and Wendy Freedman were our hosts, and Stacy McGaugh, Bill Saslaw, Alar Toomre (who did an insanely cool computer simulation of galaxy collision back in 1972!), Frank van den Bosch, and James Bullock were in attendance.) Among the many interesting things I learned is that the whole issue of Dark Matter is much more complicated than I ever imagined. I used to think that Dark Matter was simply sprinkled liberally around the universe in exactly the right quantities to get the accelerations of galaxies and clusters right. I thought, in other words, that it was a simple and straightforward Duhem problem. Then, a few years ago, the images of the Bullet supercluster collision came out, and it was widely reputed to offer direct evidence of dark matter. This made it seem like a standard "independant confirmation" of a Duhumian auxilliary hypothesis. But of course, the situation is MUCH more complicated. There are in fact at least 16 different moving parts in the Dark Matter controversy, and superclusters are just one of them. And in fact, long before the Bullet cluster was observed, opponents of the standard model of "cold dark matter" (who advocate a modified theory of gravity) had admitted that superclusters probably had missing mass. But the rub is this: there is plenty of known missing BARYONIC mass (the kind that the Big Bang neucleosynthesis model predicts the expected quantity of) to account for the missing mass in superclusters. In fact, that would only take about 3% of the baryonic mass out there, and as much as 30% is known to be missing. So, the "dark matter" in the Bullet supercluster could easily be brown dwarfs, black holes, or other "normal" stuff. So, the debate is much more intricate, and it involves trying to figure out how the dark matter halos of the universe would have evolved from the tiny fluctuations of the cosmic microwave background and then predicting what velocity curves for galaxies those would produce. The contest is then to see who can predict velocity curves better: the people with modified theories of gravity, or the people who simulate the dark matter and then see what it does. From what I can tell, the modified gravity people seem to have the edge in that, and they do with fewer free parameters. All very fascinating stuff.