Weather prediction is part of every new service. Three, maybe four days
ahead. And sometimes they're right. But what about a week ahead, or
a month? Naturally, Chaos scientists had a go at this problem. Their
conclusions are not going to be much more use if you want to choose
a fine day for your birthday party in three months!
There are many variables associated with the weather: temperature,
air pressure, wind speed, wind direction, humidity and many more.
The equations which control the weather involve all of these variables.
You can accurately put all these variables in an equation and calculate,
with some degree of certainty the value of all the variables one second
hence. These answers can be fed back in, and the values for the next
second can be calculated one second hence. These answers can be
fed back in, and the values for the next second can be calculated.
Leave the poor computer go for long enough to do the iterations and
you will know the weather one month later. Or will you?
Edward Lorenz tried this. Lorenz decided to run the program for
longer. To do so he entered the values for halfway through the run
and set the machine off again. But, the results soon deviated from
the previous run. Lorenz found the reason was that he had put the
values in accurate to three decimal places. The computer had
calculated to six places. So a difference of one in a thousand was
enough to change the output significantly. We can't measure the
variables accurately enough to avoid the effects of chaos.
For ten years, Lorenz's paper on this result was ignored, despite Lorenz
being aware that this was a crucial discovery. When he plotted the three
key variables in three dimensional space, he gained a plot that came to be
known as the Lorenz Attractor.
To download a picture of the Lorenz Attractor, please go to our download section.