Conway's Game of Life

If you looked at the top of this site, you saw a little grid of grey squares blinking in and out. That's Conway's Game of Life, and it isn't a decoration I grabbed from somewhere. I wrote it, and it's running live, right now, in your browser.

Here's what it is, and why I like it enough to put it on my homepage.

Four rules, that's the whole thing

The Game of Life isn't a game you play. It's a tiny universe with four rules, invented by the mathematician John Conway in 1970. Every cell on the grid is either alive or dead, and on each tick it looks at its eight neighbors and follows these rules:

1. A live cell with two or three live neighbors stays alive.
2. A live cell with fewer than two neighbors dies, too lonely.
3. A live cell with more than three neighbors dies, too crowded.
4. A dead cell with exactly three live neighbors comes to life.

That's it. No randomness after the start, no player, no score. You set the first frame, and the rules do the rest.

Try it

Here's the actual game from my banner. It starts from a random seed, but you can click and drag on it to draw your own living cells and watch what happens to them.

Draw a few blocks and a few lines and see which shapes survive. Some settle into still shapes that never change again. Some blink back and forth forever. And a few, if you draw them right, crawl across the screen on their own.

Why it's more than a screensaver

People have been hooked on the Game of Life for fifty years because four dead-simple rules produce endless, genuinely surprising behavior. Nobody designed the "glider," the little five-cell shape that walks diagonally across the grid forever. It just falls out of the rules. People have since built patterns inside this grid that count, that copy themselves, and even a working computer.

That's the part I find beautiful, and honestly it's why it fits a site about building software. You write a few small, clear rules, and behavior you never explicitly planned emerges on its own. The best systems I've worked on feel a little like that.

How the one on this site works

My version is a plain HTML canvas, no libraries. The grid wraps around at the edges, so a shape that walks off the right side reappears on the left. It redraws every frame and steps the simulation a few times a second. There's one small cheat: if the board almost dies out, it quietly reseeds itself, so the banner never goes empty and boring.

The cells also borrow the site's color, so they're grey in light mode and brighter in the dark. A small thing, but I like it when the details line up.

So that's the blinking grid at the top. Four rules, a surprising amount of life, and a soft spot of mine for things that do more than you told them to.