Bits and Signals: How a Wire Carries a Message

Lesson 2 · taught by Pip

Here's the plain idea: a wire can't carry your words or your photos directly. It can only do one trick — be "on" or "off." So everything you send first gets turned into a long stream of on-and-off pulses, and that stream is what actually travels.

The lighthouse out the window

Think of an old lighthouse keeper signaling a ship at night. The lamp can't speak. It can only flash: on, off, on, on, off. But if both the keeper and the sailor agree ahead of time what each flash means, that simple blinking can spell out a whole sentence.

A wire is that lamp. "On" stands for a 1, "off" stands for a 0. Each single 1 or 0 is called a bit — the smallest possible piece of information, just a yes-or-no. String enough bits together in an agreed pattern and you can spell anything.

From a letter to a string of bits

Say you type the letter "A." Your computer doesn't store a little drawing of an A. It stores an agreed-upon number for it, and that number is written in bits: 01000001. Eight little yes-or-no answers, lined up.

Every letter, every pixel of a photo, every slice of a song gets this same treatment. A picture is just a very long list of "this dot is this color" — and each of those facts is, underneath, more 1s and 0s. The whole internet is moving these streams around, nothing fancier.

How the wire actually flashes

The pulse needs something physical to ride on, and there are two common couriers.

In a copper wire, the signal is electricity: a higher voltage means "on" (1), a lower one means "off" (0). The wire flicks between those levels millions of times a second, far faster than any lamp a keeper could swing.

In a fiber-optic cable, the courier is light: a tiny laser blinks on and off, and the flashes race down a strand of glass thinner than a hair. Light is wonderfully fast and doesn't fade as quickly over long distances, which is why the big undersea cables crossing oceans are fiber, not copper.

Either way, the trick is identical to the lighthouse: a pattern of on and off that both ends have agreed to read the same way.

Why this matters

Because a message is just bits, a wire doesn't care whether it's carrying a love note, a bank balance, or a cat video — it's all the same stream of pulses to the metal or the glass. That sameness is the quiet superpower of the internet. One simple carrier, anything you can imagine riding on top.

Your turn

Find any cable plugged into your computer, phone charger, or TV. Notice it's just a path for a signal to travel. Picture it not as carrying "a video" but as carrying a fast blink of on-off-on-off — and ask yourself: who agreed what those blinks mean?

🔦 Next we'll see what happens when that stream of bits is too long to send all at once — it gets chopped into small, addressed pieces. That's the next stop: Packets, the postcards of the net.