I'll be giving a talk in Second Life tomorrow morning at 10AM pacific time. (That's Saturday, Feb 5, at 18:00 UT.) This is part of a regular talk series; follow that link to find the slides and audio recordings from most of the previous talks I've given in the series. Remember that a Second Life account is free! Come and hear the talk. You can also ask questions in text chat, which I generally try to respond to as the talk is ongoing.
Tomorrow's talk is entitled "Neutrino: Placeholder Particle". I'll talk about the history of the discovery of the neutrino. Even Pauli, the guy who proposed the neutrino, was uncomfortable with making up a new particle that nobody had seen to explain things that seemed to be missing from other observations. There are clear parallels to Dark Matter today, with many being uncomfortable that we've got most of the Universe made out of stuff that we can't identify. I'll also talk about our current state of knowledge of the neutrino, and I hope to get into the issue of how the "mass neutrinos" are not the same as the "flavor neutrinos", and even though there are three of each, there are still only three total neutrinos. (It's a Schrödingers Cat sort of thing.)
Here's the abstract I sent to Paradox Olbers, the organizer of the MICA talks:
Sometimes critics of nonbaryonic dark matter will characterize it as a "placeholder particle"-- the name we give to the fact that we can't find particles doing the things that we see happening gravitationally. Of course, dark matter is not new in astronomy; Uranus, for instance, was originally detected indirectly. Nor are palceholder particles new in particle physics. The neutrino was originally proposed more than 20 years before it was first observed. In this talk, I'll go over the history of our discovery of the neutrino, and how it was in fact astronomy that led to some relatively recent important discoveries about these elusive little particles.