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Can You Do Two Things at Once?

People say they multitask. Mostly they do not. The brain can run two tasks together only if at least one is automatic. Walking and talking works because walking is automatic for an adult. Reading and listening to speech does not, because both need the same language system. What feels like multitasking is usually rapid switching. Each switch costs time — a fraction of a second to disengage and re-engage — and the costs add up. In experiments, people doing two tasks alternately take substantially longer in total than doing them one after the other, and make more errors. They also do not notice. Switching feels efficient because you are busy the whole time. The practical conclusion is unpopular but consistent: for anything demanding, doing one thing at a time is faster.

Canals and Railways

Between 1760 and 1830 Britain built about four thousand miles of canal. Within forty years of that, most of it was losing money. A canal boat carried thirty tons behind one horse, where a cart carried two. That was transformative for coal and stone, which are heavy, cheap and not in a hurry. But a canal cannot climb without locks, cannot be built where there is no water, and freezes. A boat averaged three miles an hour. The railways did not beat canals on cost per ton at first. They beat them on speed, on reliability, and on where they could go — a railway can cross a watershed a canal cannot. Many canal companies were bought by railway companies, sometimes specifically in order to close them. By 1900 most of the network carried nothing. Some of it is now used more than it ever was, by people on holiday.