The article
The Time Eater
1On a street corner in Cambridge, England, a large clock sits behind glass in the wall of a library. The library belongs to Corpus Christi College, part of the University of Cambridge, and the clock is called the Corpus Clock. It was unveiled on September 19, 2008, by the Cambridge physicist Stephen Hawking. The clock has no hands and no numbers. Its face is a rippled disc of gold-plated steel. Behind slits in the face, blue lights in three rings show the hours, the minutes, and the seconds. On top of the disc crouches a metal creature that looks like a giant grasshopper with teeth. The inventor who designed the clock and paid for it, John C. Taylor, named the creature the Chronophage, from Greek words meaning “time eater.”
2The creature is one of the clock’s working parts. Every mechanical clock has an escapement: the part that lets the wheels of the clock move forward one small step at a time, at a steady beat. The tick of a clock is the sound of its escapement. On the Corpus Clock, the creature is the escapement. It rocks back and forth, and its claws catch in notches at the top of the disc and move it forward. Its jaws open at thirty seconds past each minute and snap shut as the minute ends, as if it were eating the minute. On the hour, there is no bell. Instead, a chain drops into a small wooden coffin hidden in the back of the clock.
3The kind of escapement the creature uses is called a grasshopper escapement. It was invented in the 1720s by John Harrison, an English carpenter who taught himself to make clocks. In Harrison’s time, sailors had no good way to find their longitude, which means how far east or west they were. To find it, they needed a clock that kept exact time on a rolling ship. Harrison spent most of his life building clocks that could keep exact time at sea. Taylor built the Corpus Clock to honor Harrison’s work.
4The Corpus Clock is strange on purpose. Its pendulum sometimes seems to catch or stop. Its lights sometimes fall behind the true time, and then race to catch up. The clock shows the exact time only once every five minutes. Taylor pointed out that people often speak of “time going fast, time going slow and time standing still.” “Your life is not regular,” he said. He also said, “I realize that time is a destroyer.” Cut into the stone below the clock are five Latin words: mundus transit et concupiscentia eius. They come from the First Letter of John, a book of the Christian Bible, chapter 2, verse 17. The King James Bible, an old English translation, gives it as “the world passeth away, and the lust thereof.” In today’s English: the world passes away, and so do the things people want from it.
5People measured time by the sky long before they built clocks. A day is the time it takes the Earth to turn around once on its axis, the imaginary line through the North and South Poles. A year is the time it takes the Earth to travel once around the Sun. That trip takes about 365 days and 6 hours. The extra quarter of a day adds up, so about every four years the calendar adds a day, February 29, in a leap year.
6The smaller pieces of time are human choices. The ancient Egyptians divided the day into twelve hours of daylight and twelve hours of night. Later, each hour was divided into 60 minutes, and each minute into 60 seconds. So a day has 24 times 60 times 60, or 86,400, seconds. For centuries, that is how the second was defined: as one part in 86,400 of a day.
7But the Earth does not turn at a perfectly steady speed. Its turning varies slightly, so a second measured by the Earth was not quite constant. Scientists found something steadier: the atom. Atoms of the same element are identical to one another, and they do not change. Atoms of the metal cesium, given just the right energy, send out radiation, an invisible wave like a radio wave, that vibrates at an exact rate. In 1967, an international conference on weights and measures defined the second as the time it takes for 9,192,631,770 of those vibrations to pass. Since then, the second has been measured by the atom, not by the Earth. By 1975, one atomic clock in the United States was steady enough that it would neither gain nor lose a second in 400,000 years.
8The largest measure of time is the age of the universe. Scientists say that the universe began about 13.8 billion years ago. They know this mainly by measuring two things: a faint glow of light left over from the universe’s early days, sent out when it was about 380,000 years old, and how fast the universe is spreading out today. From those measurements, they work back to the moment when it began.
9Taylor wanted his clock to show that once a minute is gone, no one can get it back. On the corner in Cambridge, the creature opens its jaws at thirty seconds past every minute and closes them as the minute ends.