the glider.

This little chap is called a glider, and will be instantly familiar to anyone who has seen the Life cellular automaton (CA) in action. Life was invented by the mathematician John Horton Conway at Princeton University in 1970 while seeking a distraction from his true calling, group theory. CAs are sets of rules that operate on collections of adjacent cells. These collections can be 1D (lines of cells like beads on a necklace), 2D (imagine a flat set of squares or other shapes arranged in a grid), or higher dimensional. Life is a 2D CA.

Conway wasn't the first person to think that CAs were interesting, and he wasn't the last. In fact, some rather bright sparks, like Stephen Wolfram, think that it's possible our whole universe runs as a CA.

The rules of the universe of Life are very simple. Each cell on the grid has only two states - it can be either alive or dead. Each cell is surrounded by eight neighbors, from which a new grid is calculated from the current grid at every tick of the clock according to the following:

1. If a cell is dead, and it is surrounded by exactly three living neighbors, it comes alive.
2. If a cell is dead, and it is surrounded by less than three or more than three living neighbors, it stays dead.
3. If a cell is alive, and it is surrounded by either two or three living neighbors, it stays alive.
4. If a cell is alive, and it is surrounded by less than two or more than three living neighbors, it dies.

This basic set of rules, which might seem more at home describing a boring old petrie dish, produces immensely detailed and self-organised structures built out of the living cells on the grid of Life, some capable of motion and even more complex functions. This is called emergence by a-life scientists; the fact that a large system of objects which interact with each other in simple ways can exhibit unexpectedly complicated behaviour. The complicated behaviour "emerges" out of the system even though it was never explicitly programmed in.

Our glider is just such a piece of self-organised emergent behaviour. Let's watch him evolve through a few ticks of the Life clock and see what happens...

We start off looking just like this...

After the first tick, some of the cells in the glider die, and some come alive. He mutates into a different looking shape...

After the second tick, a couple more cells die, and a couple more come alive. Hmm, deja vu...

After the third tick, the glider mutates again...

And after the fourth tick, we're back where we started.

Curiously, the glider has moved... one cell up and one cell to the left. Gliders are therefore capable of moving in a straight line around the grid of Life, one diagonal "step" every four ticks of the clock. Life is capable of producing far more complex creatures than the glider (and has in fact being proved to be capable of universal computation), but he's the simplest form to display interesting behaviour, and was the first to be noticed - earning him the arguable title of first piece of artificial life.

For more information, point your browser at the following links...

A nice comprehensive intro to Life - they also have a trendy little Java app that you can use to play with some of the more complex denizens of the Life universe.

GtkLife - a Life simulator for *nix.

WinLife32 - a Life simulator for win32.

This webspace is maintained by Quinn Reynolds 7th September 2010