Well, don't be alarmed. He is not whispering directions to you from his grave. It's just his Theory of Relativity making sure that your GPS is not making you turn a sharp left into a river! You may naturally ask how.
How do aircrafts manage to make their way and land safely? How is the military able to locate targets? And, of course, something you'll be able to relate to, how is your Uber driver able to track you using the satellite services on a phone??
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The answer is in the way satellites, some 32 of them orbiting around the earth, communicate with your local GPS (or phone) receiver to indicate your precise location. Positioning happens when the satellites talk to your device and a calculation takes place in the background. As long as the precise satellite locations are known, the time it takes the signal to travel at the speed of light gives the distance, and hence, the location of the device. If you made it through middle school math, and physics, this should sound highly doable. If not, we can dedicate a whole other article to long division.?
How your GPS works. Image - Pixabay
What makes the technology accurate is however more complicated than simple calculator math. And this is where Einstein's theory of relativity comes in. For about ten years, Einstein successfully worked on the Special and General theory of relativity, culminating his study in 1915. They were essentially maps to understanding motion, physical interactions and the concept of gravity; quite different from Newton's way of thinking.
Newton's 'apple' gravity is simply one of the consequences of the theory at low gravity situations. Nope, this is not a college lecture and you don't run the risk of a boredom attack. Maybe this will come in handy when you want to show off the brains to your next date! Much better than weather chat, trust us.
So, the general theory of relativity says that we are surrounded by an imaginary web of space and time. This web thing gets warped and stretched when you, say, sit on it. And the extent of the warp is related to how big of a mass is sitting on it. An elephant will pucker the web more than you would. And gravity is then just an expression of how much of a warp it is. Does this sound too sci-fi?ish? Well, there's proof.
All interactions, between bodies, then happen over this mesh. Say, if you were to wildly move your arms about in a swimming pool, you would see waves in the water as a result of your actions. Now imagine two massive massive black holes happily warping their part of the space-time mesh. If they were to start rotating about each other (like your flaying arms were), and then collide, there would be distortions in the mesh that would ripple out. That is a gravitational wave!
See, you already know more about Physics than your dad!?
Gravitational Waves stretching and compressing space. Light will take less time to travel between Mr.A & Mr.B, as compared to Mr.X & Mr.Y. And that difference is what an interferometer measures. Image - selfdrawn
Having established your geeky street creds, how do you know whether these waves are a real thing? Well, you see the gravitational wave squeezes space, say horizontally, while extending it vertically so that everything, including the earth's space time mesh is distorted too, as it ripples through. The only way you can detect that ripple, while existing in a compressed or expanded mesh yourself would be to measure how long it takes for light to travel between a set of mirrors. If you are along the compression, the time taken would be less, while if you are along the stretched direction, the time would be more. But this is a tiny tiny, very tiny distortion.
The wonder equipment that measures this time difference is an interferometer, known as LIGO. And in 2015, a hundred years after Einstein signed his name on the general theory of relativity, LIGO picked up a signal indicating a space distortion of 10^-19 meters (that's like 0.0000000000000000001 meters). This signal came from two black holes having collided more than a billion years ago! Talk about finding needle in an haystack the size of the universe! This very very important experiment laid bare a further proof of Einstein's theory.?
Let's move on to your GPS device, now that we have established grounds for caring about space time mesh and that different masses distort the mesh differently. So, if you had to think about it, the satellite warps its side of the mesh less than the earth, making your device and the satellite's atomic clock experience different gravities and different mesh distortion. This makes the atomic clock run a bit faster. So even if you start the two clocks at the same time, the satellite's atomic clock is going to tick quicker. And that will make your positioning way off if the relativity is not taken into account, in the background calculation of the GPS.
For feels, imagine if there was an offset of 0.001 second, your GPS would be off by 300 km.?
And that is how Einstein keeps you from landing in the Atlantic!