How Did Einstein Contributed In Working Of GPS?

How Does GPS Works?

GPS(Global Positioning System) is a satellite-based navigation system. It provides time and location-based information to a GPS receiver, located anywhere on or near the earth surface. GPS works in all weather conditions, provided there is an unobstructed line of sight communication with 4 or more GPS satellites. GPS is managed by the US Air Force.

How Did Einstein Contributed In Working Of GPS?

Einstein's theories are not just some esoteric and armchair based ideas for general consumption but have solid applications in real life. Like the prime number-based cryptography application for securing computer data and internet-based businesses using a futuristic quantum computer, Einstein's theories have similarly useful technological solutions that are system used for real life applications. One of them is the GPS that is used to navigate your car. Today, GPS is an indispensable and ubiquitous technology that helps you navigate a car or a ship or an aircraft, almost in any part of the world. My mobile phone for example, with its built-in GPS capability, tracks my every movement to within the accuracy of 10 metres. Well, without Einstein's Relativity, this would not have been possible. The great discovery that both speed and gravity make the clock tick slower, is the principle used to provide accurate measurements of one's location on Earth.

Several GPS satellites are placed in the Earth's orbit at an approximate altitude of 27,000 km and in order for these satellites to stay in that orbit, they need to move at a speed of 14,000 km/ hr relative to the surface of the Earth. This speed may not be anywhere close to the speed of light (which is roughly 300,000 km), but is still faster than any that we have seen on Earth. So, a clock aboard a GPS satellite runs correspondingly slower, about 7200 ns/day (7200x10³ seconds/day), than a clock on earth. This is a quite small, but nevertheless, this difference needs to be accounted for.

Recall that in Einstein's Special Theory of Relativity, space and time were combined into one entity called space-time. Within this space-time continuum, time slows down as you move faster. Time also ticks slowly under the influence of the gravitational field of the earth. Further, in Einstein's General Theory of Relativity, gravity too, affects the space-time fabric. For example, a clock on the surface of the Earth, where the gravitation field is stronger, will run the clock slower than in space at an altitude of 27,000 km, where the effects of gravity are less. In fact, at the altitude where the GPS satellites are positioned, the effects of gravity on time are reduced by 4%. This makes clocks run faster by a factor of 4%. This corresponds to an increase in the speed of the clock by 45,900 ns/day, which is a much bigger effect than provided by the satellite's speed.

So the net effect on time shown by the clock in the satellite, due to relativity, is an overall increase of about 38,700 ns/day. This corresponds to an error of over 10 km or 6 miles per day! If we don't correct these GPS satellite clocks to offset the errors, the GPS system in your car or mobile would take you to the wrong destination! The GPS system is well designed to take care of these errors. The GPS systems on satellites adjust the atomic clocks to run slower than they would on Earth so that the effects of relativity are nullified.