A world with a sudden limit on air travel would be tremendously different from the one we live in now.

Scientists have established huge numbers of links between particular diseases and snippets of DNA, but in the great majority of cases, this has not yet been translated into treatments that can help cure patients. These treatments will come - tomorrow, or the day after.

Smartphones can relay patients' data to hospital computers in a continuous stream. Doctors can alter treatment regimens remotely, instead of making patients come in for a visit.

A whole bunch of big technological shocks occurred when Asian innovations - paper, gunpowder, the stirrup, the moldboard plow and so on - came to Europe via the Silk Road.

The Japanese drive on the left side of the road. Most streets literally do not have names.

Historically, large-scale global trade has served two functions: 1) the exchange of goods between willing sellers and buyers described in Econ 101 textbooks 2) as a tool of state aggrandizement, in which the private parties are stand-ins for governmental interests.

Major power and telephone grids have long been controlled by computer networks, but now similar systems are embedded in such mundane objects as electric meters, alarm clocks, home refrigerators and thermostats, video cameras, bathroom scales, and Christmas-tree lights - all of which are, or soon will be, accessible remotely.