Einstein's Relativity Predicted Time Dilation and Every GPS Satellite Proves It Every Day

Each GPS satellite carries an atomic clock accurate to within a few nanoseconds. Without any correction, that clock would drift by about 38 microseconds per day relative to a clock on the ground. Thirty-eight microseconds sounds trivial. Multiplied by the speed of light, it produces a positional error of roughly 11 kilometres every single day. Leave the relativity correction out of the software, and by the end of a week your navigation app would place you in a different city.
Two separate effects cause that drift, and they pull in opposite directions. Einstein described both, one in 1905, one in 1915, and engineers had to account for both before the first GPS satellite was useful for anything.
Special relativity, published in 1905, established that time passes more slowly for an object in motion relative to a stationary observer. GPS satellites orbit at about 14,000 kilometres per hour. At that speed, the satellite's clock ticks slightly slower than a ground clock, by about 7 microseconds per day. This is velocity-driven time dilation, and it works exactly as Einstein's equations predict.
General relativity, published in 1915, added a second effect. Gravity warps spacetime, and a clock in weaker gravity runs faster. GPS satellites orbit at roughly 20,200 kilometres above Earth, where gravity is considerably weaker than at the surface. That reduced gravitational pull causes the satellite clock to run faster than a ground clock by about 45 microseconds per day.

The two effects don't cancel. They add up to a net gain of approximately 38 microseconds per day, the satellite clock running fast after both corrections are applied. Engineers pre-set the satellite clocks to tick slightly slower before launch, so that once in orbit the two effects bring them into sync with ground time. The pre-set rate is based entirely on Einstein's equations.
India's own satellite navigation system, NavIC (Navigation with Indian Constellation), operates on the same physical principles. ISRO developed NavIC to give India independent positioning capability, with satellites in geostationary and geosynchronous orbits covering the Indian subcontinent and surrounding regions. The geostationary satellites sit at about 36,000 kilometres, nearly twice the altitude of GPS satellites, which means the gravitational time dilation effect is even larger for them.

Every NavIC satellite carries atomic clocks. Every NavIC signal is corrected for relativistic time dilation before it reaches a receiver. ISRO's engineers applied the same relativistic framework GPS engineers used, because the physics does not change based on which country built the satellite. Spacetime does not negotiate.
Most experimental confirmations of relativity happen in physics laboratories or in observations of distant astronomical objects, things comfortably removed from daily life. GPS and NavIC are different. The proof runs continuously, in real time, for billions of users. Every turn-by-turn direction given to a driver in Mumbai or a delivery rider in Bengaluru depends on a relativistic correction computed from equations Einstein wrote before the aeroplane was a reliable machine.

The satellites do not prove relativity in the way a textbook experiment proves a formula. They prove it in the way a bridge proves structural engineering, if the calculation were wrong, the system would fail visibly and immediately. GPS has been operational since 1995. NavIC has been operational since 2018. Neither system has drifted into kilometre-scale error. The correction works because the physics is right.
Atomic clocks in orbit are also among the most sensitive instruments ever built. They can detect the difference in gravitational field between one floor of a building and the next. The fact that this precision is now embedded in consumer devices, phones, cars, tractors used in precision agriculture, means Einstein's spacetime geometry has become infrastructure.
The satellites were put in orbit to solve an engineering problem. What they accidentally became is the largest continuous physics experiment in human history, running above every city and field on Earth, confirming every day that time is not the fixed background Einstein's predecessors assumed it was.