Bits & Signals

Stand on a hill at night with a flashlight, a friend on the far hill. You can't shout that far. But you can agree on a code: short blink, long blink, combinations meaning letters. With nothing but light and patience, you could send a whole sentence across the valley. Congratulations — you have independently invented how every network on earth transmits, from the cable in your wall to the internet's ocean floor.

Everything becomes bits

Here's the strange, simple fact at the bottom of this course: whatever you send — a message, a photo, a movie, this very page — is first turned into bits: a sequence made of exactly two symbols, written as 0 and 1. Not ten symbols, not letters. Two.

Why two? Because two is the easiest distinction in the physical world to make loudly and read reliably. On or off. High or low. Present or absent. A flashlight doesn't need to produce twenty-six shades of "kind of on" to send your code — and a machine reading millions of symbols per second, through interference and distance, wants the same mercy. With an agreed code, two symbols are enough to spell anything: letters, colors of pixels, moments of sound. A photo is millions of bits; a movie, billions. Nothing survives the trip as a "picture" — it travels as an enormous, precisely ordered stream of 0s and 1s and gets rebuilt at the far end.

Bits need a carrier

A bit is an idea, and ideas don't move on their own. To travel, bits ride a signal — some physical thing that can rapidly flip between two states. Three carriers run the modern world:

• Electricity through copper. Voltage high, voltage low — bits as tiny electrical pulses. This is the network cable, and it's the telephone century's great-grandchild.
• Light through glass. A hair-thin glass thread — fiber optic — with light flashing on and off at rates no flashlight ever dreamed of. Light travels absurdly fast and absurdly far without fading, which is why fiber carries the internet between cities and under oceans.
• Radio through air. Waves rippling out of an antenna, patterned to carry bits. No string at all — this is Wi-Fi, and your phone's connection, and Bluetooth.

Copper, glass, air. Your flashlight-on-a-hill is the same trick as all three: a physical thing flipping between two states, fast, in a pattern both sides understand.

And note what doesn't change: the bits. The same photo rides all three carriers in one trip — radio from your phone to the box in the corner, copper through the wall, glass across the continent — copied faithfully from carrier to carrier at every junction like a letter changing trucks. The message doesn't care what it rides. That separation — what is sent versus what carries it — is one of the cleanest ideas in all of computing, and you now own it.

One habit to unlearn while we're here: bits do not "arrive as a photo." They arrive as bits, and your device rebuilds the photo. If the stream gets interrupted partway, you've seen the result yourself — the half-loaded image, the video that freezes mid-frame.

So bits can travel. Next lesson: the two carriers in your own home go head to head — the trusty cable versus the invisible radio — and you'll learn why the same laptop can feel like two different machines depending on which one it's using.