Does time really move slower in space?

Time dilation is real, measured, and built into technology you use daily. Einstein's relativity says two things affect the rate a clock ticks: how fast it is moving relative to you (special relativity, faster means slower ticking) and how deep it sits in a gravitational field (general relativity, stronger gravity means slower ticking). Both effects are tiny at everyday speeds and gravities but entirely measurable with atomic clocks, and experiments flying clocks on aircraft confirmed them decades ago.

GPS is the practical proof. Satellites orbit fast, which slows their clocks relative to the ground, but they also sit far from Earth's mass in weaker gravity, which speeds their clocks up, and the gravitational effect wins. Net, satellite clocks run ahead of ground clocks by tens of microseconds a day, and since GPS positioning works by timing signals, uncorrected drift would introduce navigation errors growing to kilometers within a day. The system corrects for relativity continuously. Astronauts experience the effect too: after long stays on the space station, they return having aged a tiny fraction of a second less than they would have on Earth, a genuine but minuscule amount. The dramatic version, where a traveler returns to find decades passed, requires speeds close to light or proximity to something like a black hole, so it remains firmly in the realm of physics rather than of travel plans.