Two identical atomic clocks are made. One is placed in the foothills of the Rocky Mountains at the NIST in Boulder, Colorado, about one mile above the sea level, and the second is flown in a GPS satellite around Earth at about 17,000 mph. Which clock gets ahead of the other?
A) The clock in orbit
B) Both clocks run at the same rate.
C) The Boulder clock

Question

Quizplus · Accepted Answer

The clock in orbit gets ahead due to the effects of both special and general relativity. Special relativity predicts that moving clocks run slower, which would suggest the clock on the GPS satellite should lag. However, general relativity predicts that clocks in a stronger gravitational field (closer to Earth) run slower than those in a weaker gravitational field (further from Earth, as in the satellite). The effect of general relativity overcomes that of special relativity in this scenario, making the satellite clock run faster than the one on Earth.

Two Identical Atomic Clocks Are Made