Thirteen Thousand Miles of Wire The Hidden Lives of Undersea Cables

The thing that carries your video call from London to New York is, for most of its journey, about as thick as a garden hose. It lies on the seabed in the dark, sometimes buried in sediment, sometimes simply draped across mud and rock. Inside it, glass fibers thinner than a pinhead carry pulses of light.

We tend to think of the internet as something in the air. Our phones connect to towers, our laptops connect to routers, and the whole arrangement feels wireless and weightless. Yet when a message leaves a continent, it almost always goes down into the ocean. Estimates vary with the method of counting, but the figures are consistently huge: somewhere over 95 percent of intercontinental internet traffic, and by some estimates 99 percent of global data, travels through cables on the ocean floor. Satellites carry only a sliver of it. Altogether, the network runs to nearly 900,000 miles of fiber-optic line, enough to circle the Earth dozens of times.

The fibers themselves are modest objects. A single strand of glass is about 125 microns across, roughly the width of a human hair. Light travels down it by bouncing along the boundary between two layers of glass, and one strand can carry an astonishing quantity of data. A modern subsea cable bundles a number of these strands together, wraps them in copper to carry electrical power, and surrounds them with steel wires and plastic for protection. In the deep ocean, where little can disturb it, the armor is thin. Near the coast, where anchors and fishing gear are a danger, it grows thicker.

This episode is about that hidden system: where it came from, how it gets laid and fixed, what tries to break it, and why governments have started to worry about who controls it. The story begins long before fiber, with copper wire, a very ambitious businessman, and a cable that worked for only a few weeks.