Alucid but not oversimplified popular account of 21st-century cosmology. In the late 20th century, work by Einstein and quantum physicists seemed on the verge of explaining everything when confusion descended. Astronomers discovered that galaxies were moving too fast. Their stars and dust produced far too little gravity to accomplish this, so most matter in the universe is not only "dark," but it can't be the particles, atoms and molecules familiar to us because even invisible normal matter is fairly easy to detect. No one knows the makeup of dark matter. If this weren't frustrating enough, in 1998 scientists discovered that the expansion of the universe was accelerating.