How Your Message Zooms Around the World in Seconds

When you send a text message to a friend in Japan, it doesn't fly through the air the whole way. Instead, it likely travels through a cable thinner than a garden hose lying on the bottom of the Pacific Ocean — and still arrives in under one second.

You will learn how a message gets broken into small pieces called packets. You will learn how undersea cables carry information between continents. You will learn what a server does when your message arrives. You will practice filling in the steps of a message's journey.

Before your text message ever leaves your phone, it gets chopped up into small chunks of data called packets — usually just 1,500 bytes each, smaller than this paragraph. Each packet gets labeled with an address, similar to writing a return address and a delivery address on an envelope. The packets don't always travel the same path. Some might zip through one cable while others take a slightly different route, but they all get reassembled in the correct order the moment they arrive.

About 99% of international internet traffic travels through undersea cables, not satellites. There are over 400 of these cables crisscrossing the world's oceans, stretching more than 750,000 miles combined — enough to circle the Earth about 30 times. Each cable is roughly as thick as a garden hose but contains hair-thin glass fibers that carry information as pulses of light, traveling at about two-thirds the speed of light.

Once your packets reach their destination country, they usually pass through a server — a powerful computer that stores and forwards information. Big tech companies build entire buildings called data centers full of thousands of servers working together. A single data center can process millions of messages every minute, checking each packet's address and sending it toward the correct phone or computer, all in a fraction of a second.