Over the past decade there has been a growing public fascination with the complex
“connectedness” of modern society. At the heart of this fascination is the idea of a network
— a pattern of interconnections among a set of things — and one finds networks appearing
in discussion and commentary on an enormous range of topics. The diversity of contexts in
which networks are invoked is in fact so vast that it’s worth deferring precise definitions for
a moment while we first recount a few of the more salient examples.
To begin with, the social networks we inhabit—the collections of social ties among friends
— have grown steadily in complexity over the course of human history, due to technological
advances facilitating distant travel, global communication, and digital interaction. The past
half-century has seen these social networks depart even more radically from their geographic
underpinnings, an effect that has weakened the traditionally local nature of such structures
but enriched them in other dimensions.
The information we consume has a similarly networked structure: these structures too
have grown in complexity, as a landscape with a few purveyors of high-quality information
(publishers, news organizations, the academy) has become crowded with an array of
information sources of wildly varying perspectives, reliabilities, and motivating intentions.
Understanding any one piece of information in this environment depends on understanding
the way it is endorsed by and refers to other pieces of information within a large network of
links.
Our technological and economic systems have also become dependent on networks of
enormous complexity. This has made their behavior increasingly difficult to reason about,
and increasingly risky to tinker with. It has made them susceptible to disruptions that
spread through the underlying network structures, sometimes turning localized breakdowns
into cascading failures or financial crises.