“‘Dark matter is what my research team is looking for. No one knows what it is. There’s more stuff out there in the universe than we can see, that’s the point. We can see the stars and the galaxies and the things that shine, but for it all to hang together and not fly apart, there needs to be a lot more of it—to make gravity work, you see. But no one can detect it. So there are lots of different research projects trying to find out what it is, and this is one of them. . . . We think it’s some kind of elementary particle. Something quite different from anything discovered so far. But the particles are very hard to detect.'”

—from The Subtle Knife by Philip Pullman