**What is the Time Dilation Effect?**

According to Einstein’s special relativity theory, time slows down for a moving object as measured by an observer considered to be stationary. The theory predicts for example that if one member of a pair of identical twins travels at near light speed to a distant star and back, he will return to find that his clock has been running slow and that his homebound brother has aged more than he has. This “time dilation” effect has been confirmed by experiment: Atomic clocks taken on long rides in space have been found to lag a few billionths of a second behind clocks that remained on Earth.