Before the eighteenth century, people crudely measured time. Galileo used his own pulse as a measure. Today, our atomic clocks can measure a time interval as small as one-millionth of a second. (Though we have a word for one-trillionth of a second— pico second —we still have no way of accurately measuring it.) But no matter how finely calibrated our clocks are, they are always measuring something discrete—an interval, a repeating signal, a duration between...
