LAST MONTH, UNITED Airlines grounded nearly 5,000 flights when its computer system crashed. The culprit: a faulty network router. Later on the same morning, another computer glitch halted trading on the New York Stock Exchange for over three hours.
Some saw the sinister hand of a hacker in these outages, but they are far more likely to be a coincidence, an intrinsic feature of the system rather than a bug. Networks go down all the time, a consequence of unprecedented levels of interconnection. Disruptions can occur even in the most robust networks, whether these are power grids, global financial markets, or your favorite social network. As the former Atlantic reporter Alexis Madrigal observed when a computer error shut down the Nasdaq stock exchange in 2013, ?When things work in new ways, they break in new ways.?
A fresh new understanding of such systems?the way they grow, and how they break?has arisen from the physics of coffee.
Researchers usually think of network connectivity as happening in a slow, continuous manner, similar to the way water moves through freshly ground coffee beans, slowly saturating all the granules to become coffee in the container below. However, over the past few years, researchers have discovered that in special cases, connectivity might emerge with a bang, not a whimper, via a phenomenon they have dubbed ?explosive percolation.?
This new understanding of how ?ber-connectivity emerges, which was described earlier this month in the journal Nature Physics, is the first step toward identifying warning signs that may occur when such systems go awry?for example, when power grids begin to fail, or when an infectious disease starts to mushroom into a global pandemic. Explosive percolation may help create effective intervention strategies to control that behavior and, perhaps, avoid catastrophic consequences.
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