SNAPSHOT OF THE UNIVERSE at age 380,000 years was taken by the Wilkinson Microwave Anisotropy Probe. Earth is located at the center of this celestial sphere. Red corresponds to warm regions, blue to cooler ones. Image: NASA/WMAP
In what is widely regarded as the most important scientific discovery of 1998, researchers turned their telescopes to measure the rate at which cosmic expansion was decelerating and instead saw that it was accelerating. They have been gripping the steering wheel very tightly ever since.
As deeply mysterious as acceleration is, if you just accept it without trying to fathom its cause, it solves all kinds of problems. Before 1998, cosmologists had been troubled by discrepancies in the age, density and clumpiness of the universe. Acceleration made everything click together. It is one of the conceptual keys, along with other high-precision observations and innovative theories, that have unlocked the next level of the big bang theory.
This article was originally published with the title Four Keys to Cosmology.