One of Albert Einstein's greatest insights was realizing that time is relative. It speeds up or slows down depending on how fast one thing is moving relative to something else. How much does it change ...

Physicists have transferred time and frequency information over a distance of more than 100 km in free space, far exceeding the previous record. The technique, which makes it possible to synchronize ...

Speed alone may be the factor that draws many sports fans to the bobsled, luge and skeleton events at this year's Beijing Winter Olympics. But beneath the thrilling descents of the winding, ...

Light is the fastest-moving thing in the universe. So what would happen if the speed of light were much, much slower? In a vacuum, the speed of light is about 186,000 miles per second (300,000 ...