FIGURE 2.19 The makeup of our universe. Two-thirds of the matter and energy in the universe is in the form of a mysterious form of dark energy that is causing the expansion of the universe to speed up, rather than slow down. The other third is in the form of matter, the bulk of which is dark and which scientists believe is composed of slowly moving elementary particles (cold dark matter) remaining from the earliest moments after the birth of the universe. All forms of ordinary matter account for only about 5 percent of the total, of which only about one-tenth is in stars and a very tiny amount is in the periodic table’s heavier elements (carbon, nitrogen, oxygen, and so on). The idea of particle dark matter was reinforced by recent indications that neutrinos have mass and thereby account for almost as much mass as do stars. Adapted from a drawing courtesy of M. Turner (University of Chicago).