Butterfly Effect

In 1961, Edward Lorenz, a mathematician and meteorologist, made an important discovery. He found that no matter how much information he gathered his weather prediction would not be correct.

He observed this by setting up a model weather system and calculating a solution. He decided he would like to study how the system worked over a longer period of time and so did a second run on the computer. Instead of starting with the same initial information of his first model weather system, he tried to save time by noting down the numbers it had reached at the middle of the original run and fed them into the computer as a new starting point. He thought the machine would repeat the second half of the original and go on from there, computing the solution for the longer period of time he wanted.

Edward Lorenz went for a coffee and when he came back several hours later the information he found on his computer changed the whole way we look at nature and the universe as well as the direction of mathematics and science forever.

He found that the new run did not repeat the second half of the first run. Although it started out the same, it slowly changed and after many computations became an entirely different set of numbers, representing a totally different weather system. Lorenz quickly realised that the major difference in the model systems occurred because of very tiny errors that he unintentionally programed into the computer by rounding off the number he had noted from the middle of the original run. That number was 0.506127. Lorenz had entered the rounded-off number of 0.506 into the computer. He did not think that the difference - one part in a thousand would change the solution. But it had made an enormous difference!

Lorenz's equations were very different from what he had expected them to be and he realised that he was seeing something very new and very important happening. He coined the famous phrase: "Butterfly Effect" to describe what he had learned. "The flapping of a single butterfly's wing today produces a tiny change in the state of the atmosphere. Over a period of time, what the atmosphere actually does diverges from what it would have done. So, in a month's time, a tornado that would have devastated the Indonesian coast doesn't happen. Or maybe one that wasn't going to happen, doesn’t.

"Does God Play Dice?", Ian Stewart