Professor Edward Lorenz died April 16th (last Wednesday). Many readers of this blog will have no idea who he was, but you will have heard of the "butterfly effect", a phrase he may or may not have coined (depending on who you ask).

From his Obituary in the Telegraph

Professor Edward Lorenz, who died on Wednesday aged 90, was a mathematician and meteorologist who was one of the early exponents of chaos theory and in particular of the "butterfly effect": the notion that a tiny event, such as the movement of a butterfly's wings in Brazil, can have enormous effects, such as a tornado in Texas.

Chaos theory became enormously influential in a host of fields besides weather forecasting. But despite its name, chaos theory does not imply randomness: chaotic systems are both deterministic and nonlinear, but show evidence of what mathematicians call sensitive dependence.

Indeed, as Lorenz was at pains to point out, chaos theory enables us to improve our knowledge of apparently unstable systems such as the weather, and thus describe and analyse them, and improve our forecasts.

[Link to full text...]

The long and the short of it, is that Lorenz showed that complex apparently random behaviour such as weather systems were actually not random at all but rather extremely sensitive to initial conditions. He very cleverly came up with three equations and plotted the Lorenz Attractor.

As his Obituary says...

The effects can be shown by a simple waterwheel, in which each bucket has an identical hole in the bottom. With a trickle of water, the wheel does not revolve at all; with a steady stream a direction to revolve is set and continues ad infinitum; but with an increased flow the wheel will spin, then slow, then change direction.

The last experiment I conducted at university was the construction of a Lorenz Waterwheel. We hooked up a bicycle dynamo and used the voltage to measure the angular velocity (speed) of the wheel. Plot velocity against position and for a pendulum you get a circle, our waterwheel drew all kinds of shapes. If we had more time (and something more accurate than a bicycle dynamo) we should have been able to get it to draw a Lorenz Attractor.

The video is five minutes long, as you watch the first couple of minutes you will think how repetitive it is. Then, just as you think you know what is going to happen next it surprises you. It surprised us again and again and again.

So a big thanks to Edward Lorenz for a wonderful experiment I would never have thought of myself. We had hours of enjoyment thanks to your genius. May he rest in peace. Amen.