Possible Dark Matter Detected

Dark matter, as you might gather from the name, is impossible to "see" (in the sense of reflecting light).  Whatever it may be specifically, it most certainly doesn't seem to interact electromagnetically with any other particles.  And so we turn to other forces to detect it - most notably gravity.  It's existence was first inferred from the inexplicably high gravitational energy necessary for the observed speeds of galactic rotations (and the speeds of galaxies in clusters).

"Hang on, Doc.  I see something that makes no sense."