Time Dilation: Clocks Disagree

Put an atomic clock on a plane flying east and another identical clock on the ground. Fly for a day, land, compare them. The airborne clock shows less time has passed — by about 60 nanoseconds.

Time dilation means faster motion equals slower time. At everyday speeds, the difference is negligible — nanoseconds over a lifetime. But at 90 percent of light speed, time passes at less than half its normal rate. At 99.99 percent, one year of travel equals about 70 years back home.