When trying to think about things to write about for this blog post, I decided to go looking around to see what other people had said on blogs about GPS. I found this one post called “6 Things You Didn’t Know About GPS” (https://medium.com/iotforall/6-things-you-didnt-know-about-gps-efb37e83bd02). As I started scrolling through it and kept seeing things we learned in class this week. You need at least four visible satellites in order to determine your exact position, the USDOD owns GPS, many industries use time from satellites to stay synched with one another, and other countries have their own versions of GPS (Russia has GLONASS, the European Union has Galileo).
However, he did call out one point that I didn’t know. Here it is:
GPS has to account for General Relativity. First, let’s review what general relativity is (I had to do some research to remind myself, so I thought I’d provide some of that information for you). Wayyy back in the early 20th century, Albert Einstein was discovering all sorts of things about space. First, he came up with the Theory of Special Relativity. The most important part of his Special Relativity for us right now is the existence of spacetime, an interwoven “fabric” of space and time. Later, in his General Relativity findings, Einstein realized massive objects, like the Earth, make a dent in spacetime like a real object would sitting on a taut piece of cloth. Along with that, objects further away from the source of gravity experience slower time than the object creating gravity itself.
Ok ok, so what does this have to do with GPS at all? Well, because the Earth makes a dent in spacetime and is the source of gravity in the area, time for satellites is actually SLOWER than time on Earth. To account for this, each satellite’s onboard clock runs 38 microseconds faster than a clock on Earth. Kind of crazy, right? I have no idea how Albert Einstein was able to come up with what he did more than 100 years ago. Kudos to him.