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Gravity warps space and time, or "spacetime". The more gravity you have, the more it warps space time. The closer you are to a gravitational force, the slower time moves. This is true of all objects that have mass such as black holes, stars, suns, and planets. Even planet earth bends spacetime.
Clocks on the ground tick slower than clocks above ground. This is true of satellites and even of commercial aircraft travellers. The difference is extremely minor but it actually means that people flying at 30,000 feet actually age more slowly than their earth-bound counterparts.
Relativity affects everyone today, and the most noticeable way is with GPS devices. GPS Satellites. GPS Satellites orbit the earth at over 11,000 miles up (or about 20,300 KHm). They are far enough away that their onboard clocks run relatively faster compared to clocks on the ground due to the effects of relativity as well as its speed (about 14,000 Km/h).
Each GPS satellite carries an Atomic clock that "ticks" with an accuracy of 1 nanosecond, or 1 billionth of a second. GPS works by calculating how much time it takes for your GPS receiver to "see" 3 different GPS satellites but Relativity screws that calculation up. To get an accurate report of where you are located, the effect of relativity must be taken into account. If these effects were not properly taken into account, a navigational fix based on the GPS constellation would be false after only 2 minutes, and errors in global positions would continue to accumulate at a rate of about 10 kilometers each day! The whole system would be utterly worthless for navigation in a very short time.
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