Yet at least with its traditional methodology engineering tends to rely on computational reducibility. For typically it operates by building systems up in such a way that the behavior of each element can always readily be predicted by something like a simple mathematical formula.

And the result of this is that most systems created by engineering are forced in some sense to seem simple—in mechanical cases for example typically being based only on simple repetitive motion.

But is simplicity a necessary feature of artifacts? Or might artifacts created by extraterrestrial intelligence—or by future human technology—seem to show no signs of simplicity?

As soon as we say that a system achieves a definite purpose this means that we can summarize at least some part of what the system does just by describing this purpose. So if we have a simple description of the purpose it follows that we must be able to give a simple summary of at least some part of what the system does.

But does this then mean that the whole behavior of the system must be simple? Traditional engineering might tend to make one think so. For typically our experience is that if we are able to get a particular kind of system to generate a particular outcome at all, then normally the behavior involved in doing so is quite simple.

But one of the results of this book is that in general things need not work like this. And so for example at the end of Chapter 5 we saw several systems in which a simple constraint of achieving a particular outcome could in effect only be satisfied with fairly complex behavior.

And as I will discuss in the next section I believe that in the effort to optimize things it is almost inevitable that even to achieve comparatively simple purposes more advanced forms of technology will make use of systems that have more and more complex behavior.

So this means that there is in the end no reason to think that artifacts with simple purposes will necessarily look simple.

And so if we are just presented with something, how then can we tell if it has a purpose? Even with things that we know were created by humans it can already be difficult. And so, for example, there are many archeological structures—such as Stonehenge—where it is at best unclear which features were intended to be purposeful.