## What does relativity have to do with life? The answer may be in your hand:)

Today, let's talk about the relationship between relativity and life.

Why, doesn't it matter? Indeed, many people will feel unfathomable and far away from life when they see the word "theory of relativity". But in modern life, there is one thing that doesn't work without relativity, and it can always be used in your smartphone.

what we are talking about here is the GPS satellite positioning system. If GPS wants to ensure the accuracy of positioning, it must be corrected by the theory of relativity.

(picture from: xkcd)

what's going on? Next, the home page invited Sheldon of the Squirrel Club to explain:

GPS positioning system has more than 30 satellites in Earth orbit. In order to accurately determine your location, your GPS positioning device needs to receive signals from at least four satellites at all times. The positioning principle of

GPS satellites is the moment when they keep sending their clocks in the direction of the earth. If a satellite is far away from you, it takes more time for electromagnetic waves to transmit, and the signal you receive will have a greater time delay. If a satellite is close to you and the transmission time of electromagnetic waves is short, the delay of the signal you receive is relatively small.

when your device receives four timestamps from four different satellites, you can infer how far you are from each of those four satellites. So you can determine where you are on earth. The accurate positioning of

GPS satellite depends on the accurate measurement of time, and in order to accurately measure time, we must consider the correction of special relativity and general relativity.

GPS satellites usually fly in the air at a speed of 3.9km per second. According to special relativity, the time of a moving object slows down, which slows its clock by 7.2 microseconds a day.

the GPS satellite is about 26000 kilometers away from the earth's center of mass, and the earth's radius is more than 6700 kilometers. According to general relativity, time passes faster in a weak gravitational field than in a strong gravitational field. The clocks of GPS satellites are 45.8microseconds faster than those on the earth's surface every day.

offset by speed, clocks on GPS satellites are 38.6 microseconds faster than clocks on Earth's surface every day.

if this time difference is not corrected, the GPS satellite positioning system will soon become unusable. As a result, GPS engineers have slowed down the clocks of GPS satellites a little bit so that they are at exactly the same rate as clocks on the earth's surface.

the difficult formulas written by Einstein in 1905 and 1915 are now silently providing each of us with a more convenient life.

minute Physics has also talked about this problem in animated short films:

I don't know what everyone is doing, but the home page is a big road nerd who can only survive by positioning and navigation. So, I would also like to thank Einstein _ (: Einstein "∠) _

for a long time, but I still don't understand what relativity is. It doesn't matter. Reading the original article will explain the theory of relativity to you in the simplest words.

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