The first use that came to my mind that affects many of us is through the use of GPS- the Global Positioning System that allows us to use Google navigation, or others to get us from one location to another. It is not as simple as it might seem.
Time is not the same on all parts of the earth, nor is it in space. It runs at different “speeds”. Sure, we all accept the time on our watches, or updates from an atomic clock that resets what we use. For our purposes time is what we perceive it to be. For me it’s the time expressed on this iPhone I am using to write this today.
Variations in Gravity due to mass cause changes in the bending of space time and hence changes in the rate with which time passes. On earth it is very, very small.
But for an object moving at high velocity, anything on that object, including an astronaut, experiences time differently even if only in fractions of a second. The faster an object moves, the greater the difference. For the astronaut time appears normal. For us on earth watching the astronaut he appears to slow down. For the astronaut looking at earth time appears on earth to speed up. It actually does. The appearance is reality.
The GPS system was originally developed by our military for use to coordinate locations of our forces on the ground. It was later adapted for civilian use. There are 24 satellites stationed around the globe at an approximate height of 24,000 kilometers, about 14,900 miles, moving at about 14,000 kilometers – about 8,700 miles per hour, orbiting earth every 12 hours. The satellites are not in geosynchronous orbit, remaining stationary over a part of the earth. Each satellite has within it an atomic clock. There are always at least four satellites visible from any spot on earth at the same time. The clocks on those satellites tick more slowly because of the effects of relativity and the satellites velocity. It is a very tiny change.
But since the satellites are also far above the earth, the mass of the earth has less effect on their time that it does at the surface- so from that perspective time runs slower on the earths surface than it does in the satellite. The two do not offset entirely the different effects. The bottom line is that they run faster by 7 microseconds, but slower by 45 microseconds leaving a difference of 38 microseconds per day. If that were not taken into account, over time they would show you to be at a different location than where you would really be. Fortunately, scientists took this into account, the satellites adjust their data, and GPS works just fine.
Any thoughts on relativity or questions on its effects?
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Originally posted 2015-10-28 06:45:25. Republished by Blog Post Promoter