Beyond days—up into the other human constructs known in English as weeks and months and years—the arrangements became wildly different according to the vagaries of religion and custom and the caprices of personalities. But it is the considered aim of modern metrologists, when dealing with matters concerning the basic unit, the second, that all of the units should agree, exactly. So far as larger units of time are concerned, all are free to do as they wish. But the second itself is sacrosanct.
Until 1967 the second was very much linked to a natural phenomenon—as the fraction of the length of the day, at the top of the top-down pyramid—by way of a sundial or by a seconds pendulum, which ticked away the duration of a day at intervals that were determined by the length of the pendulum itself. It was easy enough—if time consuming—to adjust the length of a pendulum until it ticked away at the rate of 1/86,400 of the period between two sun-at-zenith moments we call noon. Easier still to apply the equation from schooldays, of T=2π√lg where l is the length of the pendulum, g is the acceleration of gravity, and T is the time taken by each beat of the pendulum.
To deduce the second from the day is indeed easy enough. The greater problem, recognized from antiquity, is that the length of the day itself turned out to be almost infinitely variable, due to a range of reasons both local—such as the frictional effects of the tides—and astronomical—such as changes in the Earth’s rotation, the wobbling-top precession of its axis, the steady slowing (and occasional random speeding-up) of the Earth’s period of rotation. For how can a second be accurately defined if the standard against which it is measured is inherently unstable? This was James Clerk Maxwell’s singular problem, once again.
The way that this problem was first dealt with was to replace the day at the top of the notional pyramid with the much larger unit of the year—and to measure increments of time as fractions of the year, of the passage of time taken for the Earth to make one complete turn around the sun. The notion of ephemeris time was born with this decision—ephemeris time being based on the movements of the planets and the stars as recorded from centuries of observation.
Tables known as ephemerides—almanacs a less confusing term—get better and better as the years go on, because of the ever-more sophisticated observations first from telescopes and, later on, from satellites. And so, the modern concept of ephemeris time, defined by the Jet Propulsion Laboratory in Pasadena, became standard, in 1952.
A second was then defined as 1/31,556,925.975 of a year—and not just any year, but the year 1900 beginning on January 0—this last being a way of using the midnight handover of 1899 December 31 to 1900 January 1 as the starting point, and ignoring the fact that, inconveniently for some, years—being a human construct—never begin with a day labeled as 0. Our counting system does (0.5); our clocks do (00.23 h); but our calendars (January 1, never January 0) do not.
But then the year itself, based as it is on the wanderings of a planet around a star, was found to be just as arbitrary and as wanting in precision as was the day, and so better still was needed. As it happens a better solution was waiting in the wings: Maxwell’s answer. That there are things in nature, most especially in atomic and subatomic nature, that vibrate at frequencies which never, ever, ever change. Or not to any measurable degree.
Quartz, as we discovered back at Seiko, is one such. The seconds presented by a quartz-based timekeeper were unvaryingly precise seconds; and the seconds they soundlessly accumulated turned into precise minutes, precise hours, precise days.
And yet, just as with Maxwell’s argument against using a human-scale or even a planetary-scale basis for defining the meter and the kilogram, so in the latter half of the twentieth century it became clear that though quartz is good enough for the average consumer of time, it is manifestly not good enough for the scientist, nor for the national metrology institutes around the world. Which led to the evolution of the standards that are in use today, and which employ one or more members of the more recently invented families of atomic clocks.
In an atomic timekeeper the same basic principle applies—that a naturally occurring substance can be induced to vibrate at a certain fixed and measurable rate. With a quartz crystal, it was the simple and easily knowable property of its vibration under the influence of an electrical charge that made it so attractive a candidate for timekeeping. With an atom, the frequency was a more delicate thing: it required that an electron in orbit around the nucleus of a candidate element be persuaded to shift to another orbit—to make a quantum leap, or a quantum jump, this being the origin of the phrase. It had been known since the nineteenth century that when an electron performs this leap from its ground state to another energy level, it emits a highly stable burp of electromagnetic radiation.
The radiation from such an atomic transition, it was said by many physicists, was so exact and so stable that it might well one day be used as the basis of a clock. The basic concept was first demonstrated in the United States in 1949, in a precursor to the laser, the maser, and which employed molecules of ammonia.
The first true atomic clock was invented by a Briton, Louis Essen, in 1955, when he and a colleague, Jack Parry, made a model and used as its heartbeat the transition of electrons orbiting the nucleus of atoms of the metal cesium. This might seem a curious choice: cesium is the softest of all metals—almost liquid at room temperature—and is a pale gold-colored substance that ignites spontaneously in the air and explodes when in contact with water. However, it now has a use and value beyond all measure, since in transition it emits radiation at such a steady and unvarying beat that the scientists at Sèvres readily agreed, in 1967, and after much badgering by Louis Essen and Britain’s National Physical Laboratory, where he worked, that it be used as the basis for a new definition of the second.
As it remains today. The definition of the second today is quite simply, if simply be the word, the duration of 9,192,631,770 cycles at the microwave frequency of the spectral line corresponding to the transition between two hyperfine energy levels of the ground state of cesium 133. The ten-digit number, daunting though it may sound at first, is known by every metrologist worth his or her salt, and is as familiarly and frequently bandied about as might be an American telephone number, and which it digitally resembles.
Cesium clocks are now everywhere, costly and bulky though they still may be. There are said to be 320 of them, all checked against one another—the American master clocks checked every twelve minutes to eradicate nanosecond errors. All these are then checked themselves by squadrons of even more accurate timekeepers called cesium fountain clocks, of which there are a dozen, and which employ lasers to roil a mess of cesium atoms inside a steel vessel and derive even greater accuracies than their simpler siblings.
In America, the master clocks are in Maryland and Colorado; and the GPS system—the highly precise and time-based creation described in chapter 8—is given its critical time data from an ensemble of no fewer than fifty-seven cesium clocks held at the U.S. Naval Observatory* in Washington, DC, and which in turn are augmented by a further twenty-four at the formidably well-protected Schriever Air Force Base in Colorado.
The accuracy of these clocks and the claimed accuracies of even newer ones that are being constructed or experimented with at various standards laboratories around the world—the ytterbium clock being studied at the National Institute of Standards and Technology outside Gaithersburg, Maryland, being a prime example—begin to verge on the barely credible. The British Standards Institution, for example, has claimed that while the standard cesium clock has an accuracy to some 10−13 seconds, with its fine-tuned cesium fountain clock known as NPL-CsF2, the second could be measured to a known degree of precision of 2.3 × 10−16, or 0.000 000 000 000 000 23.
This means it would neither lose nor gain a second in 138 million years.
Now there is talk of quantum logic clocks and optical clocks that deliver even more remarkable figures, one with a claimed accuracy of 8.6 × 10−18, meaning that time would be kept imp
eccably for a billion years, and the charming concept of taking the fob watch from the pocket every few days and lovingly adjusting it would be gone forever, both from the human imagination and from memory.
IT IS INTO this rarefied world of precise chronometry that science has now jumped—pouring money and equipment and personnel into matters relating specifically to the measurement of the bizarreries of time—and for the simple reason, fully recognized by teams of metrologists, that time underpins everything. “Everything” even includes, it now seems, the property of gravity. A clock that is on a table just five centimeters higher than another will record seconds that are barely measurably longer—but incontrovertibly longer, nonetheless—than its partner. And this is simply because it is less affected by the Earth’s gravity, the planet’s center being that tiny number of centimeters more distant.
THIS LINK, BETWEEN time and gravity, is now proven. And this is a happenstance of modern physics that in China—where much work is being conducted on the nature of time—has a certain unanticipated charm. There is a certain delight of synchrony for the metrologists who are conducting time-related experiments in their brand-new and handsomely funded laboratories near Beijing. For outside the very front door of their research center there stands a gift from England’s main metrology institute, the National Physical Laboratory in Teddington, west of London.
It is a sapling apple tree.
Outwardly it looks quite ordinary—just one tree among a copse of others. But this happens to be a very special tree indeed. If the Beijing summers are warm and not too dry, it will bear apples of the variety known as Flower of Kent, which are said to be crunchy, juicy, and acidic. But this is not the reason. It is the tree’s pedigree that marks it out as unique.
Before the NPL gave it as a gift the apple tree’s immediate ancestor was grown from a scion that had been grafted in the 1940s at a fruit-research station south of London, which in turn had been taken from a tree in the garden of an abbey in Buckinghamshire, and which had been planted in the 1820s. This in turn was a relic of a mighty tree that had been blown down in a great historic storm that had devastated a country estate a little farther north, that of Woolsthorpe Manor in Lincolnshire.
And Woolsthorpe Manor was the home of Sir Isaac Newton. It was to Lincolnshire that Newton had fled from Cambridge in 1666—and it was here, during the summer of that annus mirabilis, that he famously observed the apple falling from the tree. It was here, and from wondering of the force that might have impelled the apple’s fall, that he came up with the notion of gravity, as a force that affected both this humble fruit and by logical extension affected the constant motion and altitude of the moon in orbit around the planet Earth.
So, Isaac Newton’s apple tree—or more properly a child descendant of it—now flowers and fruits in a Beijing garden, beside where the Ming emperors once buried their dead, where one can see the Great Wall running along the mountain ridges, and where China’s latest generation of scientists are confirming their intellectual ambitions by working out, with the greatest accuracy, the effect that gravity has upon the steady beat of time.
Where, in other words, they are trying to establish and prove a physical, traceable connection between on the one hand the mysterious force that keeps us all rooted here on Earth, and on the other the fundamental steady tick of duration. The duration by which, fundamentally, we measure everything that we make and use, and which in turn helps establish for us with unfailing exactitude the precision that allows the modern world to function.
Acknowledgments
For at least the last seven centuries the decorative brass faceplate of an astrolabe has been known as a “rete.” The word came into the English language from the Latin for “network,” and in this lexical sense it very much works, since the face of many an old astrolabe looks much like a metallic net which has been cast over the more solid wheels and gears that make up this most ancient of astronomical instruments.
The word is also employed nowadays on the internet. It denotes a mail-list, a perpetual cyber-conversation run from the Museum of the History of Science in Oxford, and which connects in an immense electronic network a worldwide group of people who are fascinated by the intersecting topics of measurement, scientific devices (astrolabes and orreries included, of course), as well as optics, cypher machines, and the dueling concepts of accuracy and precision. I joined this list back in 2016, doing so with a timid query to the effect that I was wanting to write a history of precision, and did anyone out there have any ideas?
Zounds! I was promptly flooded by a crashing wave of enthusiasm from all around the planet, from Potsdam to Padua, Puerto Rico to Pakistan, with legions of scientifically minded people offering me advice and sending me books, giving me links to academic papers, invitations to conferences and, by the score, the names of leading figures in the world of exactitudinal studies.
And so my first order of business is to thank the originators and organizers of the rete mail-list, and to honor the helpful multitudes of those who like to be known as “retians,” for getting me started. A goodly number of the names that follow were aficionados whom I first encountered through [email protected], and all were eager to be helpful in ways both great and small. Among them were:
Silke Ackermann, Chuck Alicandro, Paul Bertorelli, Harish Bhaskaran, John Briggs, Stuart Davidson, Michael dePodesta, Cheri Dragos-Pritchard, Bart Fried, Melissa Grafe, Siegfried Hecker, Ben Hughes, David Keller, John Lavieri, Andrew Lewis, Mark McEachern, Rory McEvoy, Graham Machin, Diana Muir, David Pantalony, Lindsey Pappas, Ian Robinson, David Rooney, Christoph Roser, Brigitte Ruthman, James Salsbury, Douglas So, Peter Sokolowski, Konrad Steffen, Martin Storey, William Tobin, James Utterback, Dan Veal, Scott Walker.
Many of these, and hosts of others, swiftly insisted after my first inquiry that I make contact with the two leading experts in the field of precision, Pat McKeown of Cranfield University in southern England, and Chris Evans of the University of North Carolina at Charlotte. I traveled to see both, and each proved a fountain of assistance and generosity. This book could hardly have been written without their help and encouragement, and my debt to both is considerable. Any errors or infelicities are, of course, mine alone.
During my research I visited the national metrology institutes in Britain, Japan, China, and the United States, and so wish to record my particular thanks to Paul Shore, Laura Childs, and Sam Gresham at the National Physical Laboratory in Teddington; to Gail Porter, Chris Oates, and Joseph Tan at the National Institute of Standards and Technology in Gaithersburg; to Kelly Yan at the Changping campus of the National Institute of Metrology in Beijing; and to Toshiaki Asakai and Kazuhiro Shimaoka at the National Metrology Institute of Japan in Tsukuba, as well as offer my gratitude for the valuable advice of Professor Masanori Kunieda at the University of Tokyo.
NASA scientists and other colleagues involved in both the Hubble and James Webb Space Telescopes were most helpful, including Mark Clampin and Lee Feinberg at the Goddard Space Flight Center, as well as Eric Chaisson at Harvard and Matt Mountain at AURA.
I wish also to give particular thanks to Richard Wray, Chloe Walters, and Bill O’Sullivan at Rolls-Royce in Derby; to Billi Carey of the Rolls-Royce Silver Ghost Society; to Mark Johnson, Andrew Nahum, Ben Russell, Jim Bennett, and Jenni Fewery at the Science Museum, London; to Jelm Franse at ASML in Eindhoven (as well as to my old friend Toni Tack for offering me hospitality and shelter while in the Netherlands during this expedition); to John Grotzinger and Ed Stolper at Caltech; to Steve Hindle at the Huntington Library in Pasadena (where I was briefly a scholar-in-very-comfortable-residence); to Richard Ovendon, who is Bodley’s Librarian (and occupant of what must be one of the world’s nicest offices) in Oxford; to Fred Raab and Michael Landry at LIGO, Hanford; to Jessica Brown of Northrop Grumman; to Keiko Naruse and Takashi Ueda of Seiko; to Stefan Daniel of Leica—and my old newspaper colleague Chris Angeloglou, a formidable Leica collector.
Stephen Wolfram and his colleague Amy
Young, both immensely knowledgeable about precise measurement, provided wise counsel (and in Amy’s case, a gift of Christmas cookies). Jeremy Bernstein, expert on all things nuclear, told me much about plutonium. Max Whitby, a friend of forty years, offered fascinating insights into the world of nanotechnology. And the Master of my old Oxford college, Roger Ainsworth, turned out to have been a lead member of the Rolls-Royce Blade Cooling Research Group, and offered valuable reminiscences. Ann Lawless of the American Precision Museum, in Windsor, Vermont, was a supporter of this book from its inception. The writer Witold Rybczynski and the filmmaker Nathaniel Kahn also expressed interest and encouragement, for which I am most grateful.
My son, Rupert Winchester, an always keen and close reader, provided invaluable commentary on the near-finished script, as he has for nearly all of my books.
I cannot speak too highly, nor too warmly, of my new editor at HarperCollins, Sara Nelson, who brought her years of expertise to bear on the initial manuscript and turned it into a finished document of which I am now cautiously proud. It has been the greatest pleasure to work with her, and we have achieved a rapport, I believe, which will now endure for many years to come. Her assistant Daniel Vazquez, succeeded in the closing weeks of this book’s birth-canal progress by Mary Gaule, both proved more than worthy of Sara’s confidence in them, and proved a delight to work with. Likewise, across in London, my HarperCollins editor, Arabella Pike: we are new to each other—but the fact that she bought for her young son a set of Jo blocks as a Christmas gift, and after reading about them in these pages, suggests that a long and happy friendship is in the making.
My thanks as always to my agents at William Morris Endeavor, Suzanne Gluck in New York and Simon Trewin in London, as well as to Andrea Blatt, Suzanne’s assistant. Your tenacity and persistence are deservedly the stuff of legend, and as a beneficiary I am hugely grateful. For that, of course, but on a higher level for your friendship too, and which I know will long endure.
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