Someone can be in New York and another person in Sydney or something like that and be interacting with each other instantly from across the world. How can we connect so fast and how does the connection know to keep that connection with just me and him and not get interrupted
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Electricity travels at a significant fraction of the speed of light – scientists think now that it is less than previously thought, but still somewhere in the range of 60-80% of the speed of light. To keep things easy, we can go with 50% of the speed of light because dividing by 2 is easy.
The speed of light is 299,792.458 kilometers per second. If we want the math to be easy we can round that up to 300,000 km/s and then halve it to 150,000 km/s.
The earth’s equator is about 40,000 km in circumference.
To go around the earth will take an electrical signal somewhere close to 4/15 of a second, which is somewhere between 1/3 and 1/4 of 1 second.
There are other factors that can slow down that speed, but we’re still dealing in really fast speeds over comparatively short distances, which leaves the delay shorter than is really noticeable to most people.
As for how the connection knows to stay between you and him: in the old days, that would be the job of switchboard operators – they would literally plug the end that connected to your line directly to theirs, or in the case of long distance calling assign one of the lines that goes between areas for however many hops you needed to go (and back then the equipment was worse and there was more interference so there was appreciable delay) – nowadays that is controlled by computer software and hardware specifically designed to handle that transfer of data. More than likely your data packets are being sent out with either a TCP/IP wrapper or a UDP wrapper, which contains the IP address information of the place you’re connecting to.
The specifics of TCP/IP and UDP are a bit beyond this ELI5 needs to be, but they are different protocols that will let computers talk over the internet, by telling the computers connected between them how to route that data based on what IP address it is going to and other rules that programmers built to handle all that routing information.
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