system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Please: How does a cell phone work?

Aside from magic, how does a tiny little device in my hand send my voice to a receiver that is hundreds of yards away, and then to my parents 3000 miles away INSTANTLY?  How does that tiny receiver on top of a building sort through all of the thousands of calls coming and going simultaneously?
gpt
Firstly cell phones communicate via radio waves.  Radio waves are similar to waves on water.  Imagine you are standing on one end of a pool, and you slap your hand on that side of the pool.  It will cause a ripple (a little wave) to go out in all directions, including to the other side of the pool.


So now you can send a wave out to the other side of the pool. This is just like your cell phone sending a radio wave out. So how does that radio wave get turned into a phone call? It goes out in all directions until it hits something called a cell tower, which relays it to someone else. But how does the cell tower know what you're saying and who you want to talk to?


Imagine you could control how hard you slap the water so that you could control the size of the waves that reach the other side of the pool. Some of the waves you make could be small, some large. Now imagine there is someone standing on the other side of the pool.  You want to talk to them with waves, so you've arranged a "wave language" where one big wave means one thing, and one small wave means something else. We'll say this big wave represents the number 1 and the small wave represents a 0.  So if we send out a series of 8 waves it could look like this: 10010010. We could then make up a secret language where for every set of 8 waves we can send a small message to the other side and they can understand it.  Eventually you could combine a bunch of small messages in different combinations of 1s and 0s so that you could communicate almost anything.


So you're cell phone translates who you are, who you want to call, and what you want to say into these 1s and 0s (this is called binary) and tells the cell tower, who then communicates with who you're calling and relays the message to the other person. This goes back and forth til one of you hang up!

Now here's the neat thing.  When you splash the water it'll take a second or two to get to the other side.  Radio waves are actually made out of an invisible light, like a flashlight that you can't see, but the cell tower can because it knows how to look for it.  And this means they move at the speed of light, which is REALLY fast, almost instantly.


The cell tower sorts through the calls by using computers. When a new radio wave comes in for a new call, it assigns it to a computer to handle and goes back to looking for new waves.  This happens so fast that it will rarely miss a call!