David Matsumoto, a psychology professor at San Francisco State University, trains national security officials and police officers to recognize "microexpressions"--fleeting, split-second flashes of emotion across someone's face. Matsumoto says those subtle cues may reveal how an interview subject is feeling, helping officials to hone their line of questioning.

Saul Perlmutter shared the 2011 Nobel Prize in physics for his discovery that the universe was expanding at an accelerating rate. Perlmutter explains how supernovae and other astronomical artifacts are used to measure the expansion rate, and explains what physicists are learning about "dark energy" — the mysterious entity thought to be driving the acceleration.