You are in
New York, NY

Have you ever wondered, though, about the very intricate set of technologies that allow you to know this?

Start

Right now, there are around 24 satellites orbiting Earth. When you request your location, 3 satellites get to work.

Next

These satellites calculate their distance to your device. This creates an intersection that is used to locate your position relative to Earth.

Next I don't get it

The first two satellites are in charge of locating your position on Earth. The third, your altitude. That’s right, the GPS network is also tracking your vertical position on Earth.

Got it Still don't get it

Try this video.

Got it I give up

But there is a problem

If the position of these satellites was calculated using traditional physics, your location would be inaccurate by 11Km.

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This is because time on GPS satellites runs 38,7000 nanoseconds faster, which might not seem as a big deal, but let’s remember this is precision work. The difference in time is the result of relativity, a set of two properties of nature that affect space and time.

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General Relativity

Time is affected by gravity. The stronger gravity a cosmic object has, like Earth, the slower time will run there.

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Below is a demonstration of how increasing gravity on Earth would make time run slower in comparison to the Satellite. Try increasing gravity to 2x, and then to 10x.

Satellite

11:16:30 AM

May 14th 2015

Earth

11:16:30 AM

May 14th 2015

x gravity

Next I don't get it

Time runs normally on the satellite because this object is outside of Earth’s gravitational pull. Interesting enough, for people on Earth time seems to run normally and for them the satellite's time would be running faster.

Got it Still don't get it

Perhaps this video will help you understand.

Got it I give up

In the case of the GPS satellites, being 19,000Km above Earth and its gravitational pull, time runs 45,900 nanoseconds faster.

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Special Relativity

Time is also affected by motion. The faster one moves, the slower the time will run for them. Because no one yet can travel fast enough, this difference is imperceptible on a daily basis. But what if we could travel fast enough?

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This time we’re increasing the speed of the satellite to show how time passes on Earth in comparison. You should try 50% and then the maximum value.

Satellite

11:16:30 AM

May 14th 2015

Earth

11:16:30 AM

May 14th 2015

% speed of light

Why not 100%?

Next I don't get it

Both the satellite and planet Earth perceive time equally. But this experiment is ran from the perspective of the satellite, where time is running slowly, causing time on Earth to run faster in comparison.

Got it Still don't get it

Check out this video.

Got it I give up

Nothing in physics stops you from getting as close as you want to the speed of light. But reaching 100% is impossible. The faster something travels, the more massive it gets, and the more time slows – until you finally reach the speed of light, at which point time stops altogether. And if time stops, well then, so does speed. And so nothing can travel faster than the speed of light. Source

Ok

Going back to the GPS satellites: they travel at 14,000Km/h causing time to run 7,200 nanoseconds slower in comparison to time on Earth.

Next

Now

Let’s combine the two time differences for the satellites.

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Remember that inaccuracy of 11km? If a devastating earthquake were to strike Hell’s Kitchen, first responders would find themselves delivering much needed aid to Park Slope. So much for the victims!

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Conclusion

If it wasn’t for Relativity, you wouldn’t know where you are.

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