If you stay on Earth while a friend races off in a rocket at close to the speed of light,then,according to special relativity,you will see a clock on the rocket appear to tick more slowly than the one on your wall.If your friend looks back at your clock,then,according to the same theory,the friend will see your clock appear to tick:

Question

Quizplus · Accepted Answer

According to special relativity, time dilation occurs for moving objects. An observer in a moving frame of reference will see clocks in a stationary frame of reference ticking slower than clocks in their own frame of reference. This is a reciprocal effect, so the friend in the rocket will also see the clock on Earth ticking slower than the clock on the rocket.

If You Stay on Earth While a Friend Races Off