Chapter XII · Act III — Owning Time
Now
2010 – present
Handmade records, smartwatches and the atomic second now coexist; precision is no longer the goal, and still it advances.
Today the watch that takes years to make by hand, the smartwatch and a second no longer measured by looking at the sky, but by counting the oscillations of an atom’s radiation, all live side by side. The line that began as a shadow ends as a wave.
The caesium fountain
This flight: 0 oscillations
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A caesium fountain clock, in outline. The flight up and down lasts about a second.
- 1Lasers
- 2Cloud of atoms
- 3Microwave cavity
- 4Detector
Six lasers slow a cloud of caesium atoms to a few millionths of a degree above absolute zero, and toss it a metre upwards.
The cloud rises, crosses a microwave cavity, slows, and crosses it again on the way down.
If the microwaves oscillate at exactly caesium’s frequency, most of the atoms come back changed in state.
A laser makes them glow and a detector measures the light. It is repeated, tuning the frequency until they glow brightest: that frequency defines the second.
Since 1967 the second has been the duration of 9,192,631,770 periods of the radiation of caesium-133. These are the ones that have passed while you read this page.
Now
The first caesium clock
Louis Essen and Jack Parry set the first practical atomic clock running at the National Physical Laboratory in England. With it, Essen and William Markowitz measure the astronomical second in oscillations of caesium: that figure has defined the second since 1967.
The Grandmaster Chime
Patek Philippe marks its 175th anniversary with twenty complications in a reversible wristwatch with two dials. In 2019 a unique steel piece is auctioned for over 31 million dollars: no watch had ever sold for so much.
The smartwatch
The Apple Watch goes on sale. By 2019 more are shipped than Swiss watches of every brand together: some 31 million against 21, by Strategy Analytics’ estimate. The mechanical watch carries on, as an object of culture.
Galileo
Europe opens the services of Galileo, its network of navigation satellites. Each satellite carries four atomic clocks, two hydrogen masers and two rubidium: a receiver knows where it is because it knows what time it is.
The Berkley
Vacheron Constantin unveils in Geneva a pocket watch with 63 complications and 2,877 parts, after eleven years of work. It is the first with a Chinese perpetual calendar.
Farewell to the leap second
The General Conference on Weights and Measures decides that from 20 May 2027 civil time stops waiting for the Earth: no more leap seconds, and the gap with its turning may grow to an hour. Since 1972, 27 had been added.
The Line of Precision
The error a day of each chapter’s clocks, on a logarithmic scale. The line moves on with the story: each chapter draws its own stretch.
This chapter’s precision
- Caesium fountain2014
- ≈ 1 s in 300 million years
- Optical lattice clock2015
- ≈ 1 s in the age of the universe
- c. 1390 BCE: Clepsydra, ≈ half an hour a day
- c. 1386: Foliot tower clock, ≈ 15 min a day
- 1656: Huygens’s pendulum, ≈ 15 s a day
- c. 1715: Graham’s regulator, a few seconds a week
- 1761: Harrison’s H4, 5 s in 81 days
- 1889: Riefler regulator, ≈ 0.01 s a day
- 1921: Shortt-Synchronome clock, ≈ 1 s a year
- 1955: Essen and Parry’s caesium, ≈ 1 s in 300 years
- 1969: Quartz wristwatch, ≈ 5 s a month (a reference, not the best instrument of its time)
- 2000s: Mechanical chronometer (COSC), −4 / +6 s a day (a reference, not the best instrument of its time)
- 2014: Caesium fountain, ≈ 1 s in 300 million years
- 2015: Optical lattice clock, ≈ 1 s in the age of the universe
Squares are wristwatches and chronometers, not the best clock of their age: the line rises with them because the chapter tells their story.