I learned from a colleague today that recent astrophysical observations may provide another line of evidence for the existence of dark matter — the almost totally inert “stuff” that that, from indirect inferences, seems to make up most of the mass of the universe. Despite the fact that the nature of dark matter is considered one of the big mysteries in physics, and the fact that I’m a physicist, I don’t really care.*
Why? An illustration: A few years ago I read The Golden Compass. (Yes, it’s a kid’s book. All the Proust novels were checked out.) Dark matter plays a key role in it, as a substance that links wildly different universes, and other things. Reading it, it struck me as sad that the real dark matter, whatever it is, won’t be nearly as interesting. It will be some particle, with some mass, and maybe another property or two to be tabulated in some particle data book. It will couple to gravity, but that’s about it. That’s why it’s “dark,” and why it is therefore guaranteed to be fundamentally dull. (I hold the “condensed matter physicists” view that everything interesting, from iron atoms conspiring to make magnetism to lipids working together to make membranes, comes about because of interactions.)
But: Another colleague pointed out a new paper that puts forth the idea that gravitational interactions with dark matter perturb the cloud of comets around the solar system, driving the bombardments that are probably responsible for the (roughly) periodic mass extinctions on Earth. When I was in college, I read Richard Muller’s fascinating book Nemesis, about his hypothesis that the sun has a dim companion star that periodically nudges comets and, as above, drives extinctions. Muller and others never found such a star, and the whole idea, highly speculative, has never really gone anywhere. The dark matter idea is even more speculative, and, in fact, my colleague who pointed it out was mocking it.
Still, if there’s any chance at all of a meaningful connection between dark matter and the extinction of dinosaurs, I’m happy about it!
* Fun fact: my first paper even mentions dark matter in the galaxy! [http://scitation.aip.org/content/aapt/journal/ajp/66/9/10.1119/1.18956]