Fast-moving clocks run slow

Fast-moving clocks run slow

Now let’s look at the satellite’s clock. The satellite flies at about 13,900 km per hour. Einstein worked out that the faster a clock moves, the slower it ticks. Do the math, and a satellite clock falls behind ground clocks by about 7.2 microseconds a day. But there’s one more thing that changes how fast a clock runs.

Why?It feels like time flows the same for everyone, but this has been checked by experiment. Tiny particles racing at nearly the speed of light survive much longer than when they’re sitting still, because their time runs slower. A satellite moves about 77,000 times slower than light, so the difference is very small.

Learn moreThis is called “special relativity.” Einstein published it in 1905. The satellite on screen is drawn going around much faster than in real life.

Time lost each day because of speed

−7.2 μs

textbook formulas