The number of potentially habitable planets in the universe is crazy big (10 billion trillion).
With all those worlds, it seems pretty reasonable to suppose that life will get started on some of them. And, going further, evolution will then do its work — leading some species all the way up to forms of tool-building intelligence.
But given an intelligent species — think apes or even birds or octopus — what does it take to make the transition up to a civilization?
The emergence of civilizations from the backdrop of an intelligent species is a critical question, if you're thinking about life in the universe. But it's also a fascinating question from the standpoint of what's called "complexity theory" — and that's the approach my collaborators and I are taking in a new project.
There are lots of ways to think about a civilization. If you focus on human beings, then you'll want to include their psychology and sociology. You may even need to include aspects of their biology (i.e. reproductive strategies). But if you want to consider the problem from its most general point of view, then you might want to think about civilizations purely as a network.
A network is nothing more than a group of objects (called nodes) and the links between them. Everyone is familiar with social networks — your friends and their friends and their friends, and so on. The bigger a network is the more complex it becomes, with links blossoming into a rich, dense, spider web of connections between the nodes.
Any population of intelligent creatures on any planet would, by definition, form a network. The only way they could not be a network would be if they had no interaction with each other (no links). In that case, it's hard to imagine how they might end up forming a civilization. So the question then becomes: What exactly does it take to transform a bunch of intelligent social organisms, with more rudimentary forms of interaction, into something more complex and rich — like a city with its highly ordered interactions?
The cool thing about asking the questions in terms of networks (or what is known as "network theory") is it should allow us to ask questions about civilizations in generic ways. In that case, we could skip speculating about alternative sociologies. After all, who the heck knows how creatures on Altair IV might deal with issues like morality or religion?
But maybe, just maybe, by focusing on the nature of their interactions in a network framework we might be able to see how those creatures on Altair IV became a civilization. What that means is we could explore how broad classes of social structures that are possibly needed for civilizations — like certain kinds of hierarchies — emerge on their own from simple rules about nodes and links. And what we really want to know is: Might this kind of emergence of structure be generic? That would mean it's relatively independent of the specifics of any particular species that's grown from having just intelligence to full civilization-building.
Now it is possible that the details of biology and evolutionary history are so deeply imprinted in each species that there are no generic rules for how civilizations emerge. That's something we're watching out for as we complete this work. But the beauty of networks and complexity science is that they offer the hope of, and a path towards, seeing the underlying patterns even in nature's richest creations.
Adam Frank is a co-founder of the 13.7 blog, an astrophysics professor at the University of Rochester, a book author and a self-described "evangelist of science." You can keep up with more of what Adam is thinking on Facebook and Twitter: @adamfrank4