Networks that are resilient on their own become fragile and prone to catastrophic failure when connected, suggests a new study with troubling implications for tightly linked modern infrastructures.
Electrical grids, water supplies, computer networks, roads, hospitals, financial systems--all are tied to each other in ways that could make them vulnerable.
"When networks are interdependent, you might think they’re more stable. It might seem like we’re building in redundancy. But it can do the opposite," said Eugene Stanley, a Boston University physicist and co-author of the study, published April 14 in Nature.
Most theoretical research on network properties has focused on single networks in isolation. In reality, many important networks are tied to each other. Anecdotal evidence--the crash of communications networks in lower Manhattan after 9/11, the plummeting of markets around the world after the Black Monday stock market collapse of 1987--hints at their fragility, but the underlying mathematics are largely unexplored.
The Nature researchers modeled the behavior of two networks, each possessing what's known as "broad degree distribution": A few nodes have many connections, some have an intermediate amount of links and many have just a few. Think of the networks as having only a few branches, but many leaves. On their own, such networks are known to be stable. A random failure is likely to disable a leaf, leaving the rest of the network's connections mostly intact.
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