Now where did I put my keys?

One of the most astounding facts about the universe is that we can only observe four percent of it from our perch on Earth. Electromagnetic radiation carried along in microwaves, or in the color spectrum visible to the human eye, or by gamma rays, can be detected with the right instrumentation, either on earth or from stationary points near Earth. Roughly 23 percent of the cosmos is constructed of a mass that we can't directly detect.

Seventy-two percent of the cosmos' total mass-energy is "dark energy," the so far mysterious force pushing the observable universe outward at fantastic speeds.

Using one ready example to illustrate why that latter fact should interest us - or least the absent minded among us - Astronomer Adam Riess, MacArthur Fellow for 2008, explains his work.

Reiss is working on ways to experimentally discover the nature of dark energy.