Unless you’re totally disconnected from the world around you, you’ve noticed by now that everything in the world around you is connected — in a network.
It’s not like the old days, when the “networks” were designated by acronyms for companies producing TV shows. Networks are more diverse now, consisting of any system of nodes connected by links: Web pages and hyperlinks, electric power plants and transmission lines, actors in movies with Kevin Bacon. Since the late 1990s, scientists have been analyzing every sort of network they can think of or think up: networks of terrorists, networks of disease transmission, networks of genes, proteins or nerve cells, banking networks, social networks, transportation networks. Every-thing that isn’t utterly isolated is part of some network or another. Studying networks, figuring out how they work and how they fail, can lead to more efficient systems for travel or communication and better defenses against terrorism and epidemics.