As we touched on in the last chapter, the apple cart of cosmology was upset in a brutal and surprising way in 1998, with the observations of distant supernovae, exploding stars, by two big teams of research astronomers. Their discovery revealed the mysterious force that is accelerating the expansion of the cosmos and came to be known as dark energy. This is a crucially important area of cosmology and astrophysics, as recent observational results suggest that approximately two-thirds of the energy/mass of the universe consists of dark energy. So for the last 17 years, astronomers have realized they know very little about what most of the universe is composed of.

The discovery took the astronomy world by storm. But the seeds of the dark energy idea began much farther back in time, to be precise in 1915, actually a century ago. Prior to this, the universe was one of mechanical physics, of Isaac Newton's absolute, predictable cosmos that worked like a clock, independent of other factors. In 1905, German physicist Albert Einstein (1879–1955) began to overturn this, with his Special Theory of Relativity. In 1915, Einstein, late in the year, presented his General Theory of Relativity to an audience in Berlin. Einstein, driven in something of a race with potential competitors, unveiled his equations that not only introduced relativity but also described how space-time is distorted by mass, how mass moves around in gravitational fields, and the many forms of motion in the cosmos as observed by different frames of reference.

Einstein freed the world from seeing the universe in a Newtonian way, a cosmos beset by hard, unchanging geometry and now transformed from fixed coordinate grids to a changing, dynamic system in which space and time are linked and transform in various ways as codependents. That most important Einsteinian equation, E=mc2, was merely the simplest, and it did indeed reveal that matter and energy in the cosmos are coequals, the same thing, in different forms, and that matter can be converted into energy and vice versa. (Your metabolizing this morning's breakfast is one proof of this.) But Einstein provided many other field equations that supported his theories, and he did not ultimately solve them all.