## Distortion of spacetime

Distortion of space and time by gravity, and the Global Positioning System... For more than 200 years, the Newtonian theory for gravity reigned supreme as the correct description of the most familiar force of Nature, gravity. At the beginning of the 20th century, the story changed dramatically: the theory of General Relativity, developed by Einstein, dethroned Newtonian gravity as the correct framework for the gravitational force. One of the most interesting and beautiful aspects of this new theory purports that the fabric of space and time is malleable... mass/energy bends space and time around it! For example, a massive star would change the measure of distance between two nearby fixed points as it pulls on and distorts the space in its neighborhood. The effect is larger for more massive stars, but is also present around our own Earth. Our planet's gravity distorts time around it in such a way that time runs faster at higher altitudes... Astronauts who live about a year in the space station - in orbit about 300 km above sea level - come back a few microseconds older than otherwise... While this is a small effect, it is very important for the functioning of the Global Positioning System (GPS). GPS is all about measuring time accurately: you locate yourself with a GPS device by measuring the time it takes for a signal to travel from your handheld device to four other satellites above your head. This measurement needs to be highly accurate given that the signals travel at the speed of light. If the distortion of time by Earth's gravity is not taken into account, GPS's accuracy will go down from a few meters to many kilometers! Simply put, GPS is the first technological application that relies on the theory of General Relativity! Check out this video to satisfy your curiosity more:

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