But what science could not reliably say was whether, in any particular part of the country, clouds would congeal to block the view-a cosmic April Fool's joke. Some of the greatest phenomena, like the coursing of comets around the Sun, are marvelously predictable. But some of the most mundane, like the weather, are so convoluted that they continue to elude the most diligent forecasters. They are what scientists call complex systems. Whether cells interact to form a organism or organisms to form an ecosystem, or gas molecules interact to form a weather front, the result is what people intuitively consider complex.
People think they know it when they see it.
Everybody talks about it. But nobody knows what it really is. In the absence of a good definition, complexity is pretty much in the eye of the beholder. Human brains like to describe themselves as the most complex objects in the known universe. We human beings like to think that we're very special.