Retroreflectors left by Apollo astronauts allow precise laser ranging. Scientists measure Earth-Moon distance to millimeter accuracy. These measurements test general relativity predictions. So far, Einstein has been right. The Moon’s orbit behaves exactly as predicted. It’s one of the best gravitational experiments ever built.
This matters because fundamental physics underpins all technology. GPS, satellites, and space travel depend on relativity. The Moon keeps it honest.
It also shows the lasting value of Apollo. Decades later, those mirrors still advance science. Exploration pays long-term dividends.
Laser ranging has confirmed relativity to parts per trillion. Few experiments are that precise.
NASA [nasa.gov]