The submarine fibre-optic cable

technology

The physical article that carries almost all intercontinental data, and the first surprise about it is how small it is. In deep water, where nothing much is expected to disturb it, a modern telecommunications cable is an unarmoured "lightweight" type of roughly 17–20 mm diameter — industry descriptions reach for a garden hose or a beer-bottle cap — weighing on the order of 0.7 kg per metre in air. Inside that sheath there is very little: a few pairs of glass fibres, each thinner than a human hair, held in a steel or polymer tube filled with water-blocking compound, wrapped in a helical layer of high-tensile steel strands that carry the tension of laying rather than the traffic, then a copper conductor tube that carries electrical power to the repeaters, then insulating polyethylene. Approaching land the same cable is rebuilt for a different threat: single or double layers of galvanised steel armour wire take the diameter up toward 50 mm and the weight toward 4.8 kg per metre, because the shallow shelf is where trawl doors and anchors are, and it is ploughed into the seabed to a depth typically quoted as one to three metres. The design logic is worth stating plainly, because it explains most of what follows: the cable is armoured where people are and almost naked where they are not, so the system is engineered around human interference rather than around the sea.

A technology is not a place. Drawing it on a map would assert something about the world that no stored fact supports.