In this video I will explain how scientist used GPS to show that special and general relativity are real. Scientists have to take into account because of the effects of special relativity: time on satellites is LESS than time on Earth. And because of the effects of general relativity: time on satellites is GREATER than time on Earth. And if the scientists do not adjust for both (unfortunate the “LESS than” and “GREATER than” do not cancel each other out), we will find ourselves somewhere else other than where GPS says we are!