After seeing Steven Spielberg's "Disclosure Day," check out these real-life accounts of strange aerial sightings.

Scientists are on the trail of a mysterious five-particle structure that could challenge one of the biggest theories in physics: string theory. This rare particle—never seen before and predicted not ...

In 1980, Stephen Hawking gave his first lecture as Lucasian Professor at the University of Cambridge. The lecture was called "Is the end in sight for theoretical physics?" Forty-five years later, ...