Extremely accurate time is increasingly critical. This place is in charge of it.

If you've ever been mystified at the term 'atomic clock,' or wondered what quartz has to do with time, this is the lab with the answers.
Photograph by Dejan Krsmanovic, Alamy
By Dominic Bliss
Published 17 Jun 2021, 11:40 BST, Updated 18 Jun 2021, 12:42 BST

Teddington, on the southwestern edge of London, is home to three of the most precise clocks on the planet. They are accurate to one billionth of a second per year. So accurate, in fact, that for them to lose or gain just one second, they would need to keep ticking for the next 14 billion years; until the end of the universe. Bear that in mind when you’re next changing the batteries in your wristwatch.

These clocks, housed inside the UK’s National Metrology Institute – the centre responsible for developing an maintaining measurement standards and itself located at the National Physical Laboratory – are known as optical atomic clocks, and they’re more accurate even than the previous generation of caesium atomic clocks. Of course they bear no resemblance whatsoever to any timepiece you might wear on your wrist or set atop your mantelpiece. There are no hands or clock faces or spinning wheels or any of that mundane horology.

One of the three, for example – called a trapped ion optical clock – is an elaborate mass of bolts, plugs, wires and switches, filling an entire room. Central to it all is a cylinder the size of a small beer barrel, with a printed paper sign on top of it, stating: “NPL Sr+ ion end-cap trap”.

“Many aspects of British industry and society need increasingly accurate timing to function properly.”

NPL obviously stands for National Physical Laboratory, while Sr is the chemical symbol for strontium, an alkaline earth metal. Inside this clock, physicists have found a way to trap a single ion of strontium inside a vacuum, before cooling it with laser beams almost to absolute zero, and then measuring the frequency at which it absorbs light. Overall, this makes for an extraordinarily accurate clock. (Of the other two optical clocks, one uses ytterbium ions and the other a strontium lattice to measure time.)

Another timing-based project at NPL is something called the National Timing Centre. Rolling out over the next five years, this aims to improve the security and reliability of the many British technologies that rely on split-second timing: London’s financial trading, for example, and global navigation satellite systems (such as GPS), telecommunications, TV and radio broadcasting, and the energy industry. In the future it will aid autonomous vehicles, 5G cellular networks, and smart cities.

Atomic clocks work by using the resonance of an element – in the case of this clock ...

Atomic clocks work by using the resonance of an element – in the case of this clock at the National Physical Laboratory, Cs, for caesium – to measure and keep time. Certain elements, including caesium 133, resonate extremely consistently both independently, and with other examples of the same element. This resonance can therefore be used as highly accurate yardsticks for precise increments of time. In the case of caesium 133, it resonates at 9,192,631,770 cycles per second, meaning one second can be defined (and divided) by this figure. Many wristwatches use the same oscillations in a quartz crystal to do the same thing, though rather less accurately, at 32,768 oscillations per second. The most simple is the pendulum, which oscillates at an interval defined by its length and weight. Clock and watch movements are then configured from this to move incrementally when the oscillations equate to a predefined period – for instance, a second.    

Photograph by David Gee, Alamy
Not a hand or a clock face in sight: A computer screen displays the time generated and kept ...

Not a hand or a clock face in sight: A computer screen displays the time generated and kept by the atomic clocks at Teddington's NPL. 

Photograph by David Gee, Alamy

Eventually the National Timing Centre programme will have four secure sites around the country, working together to provide deeply accurate timekeeping. One will be at NPL, in Teddington; another will be announced in the near future; for security reasons, the locations of the final two will likely remain undisclosed. In addition to these, there will be several timing devices dotted around the UK, offering super-accurate timing to any British industries or private companies that require it. Called customer access nodes, these might eventually be positioned on the side of smart motorways, for example, or in telecoms factories, or in banks.

Splitting seconds

But why do atomic clocks need to be quite so astonishingly accurate? After all, what are a few nanoseconds between friends?

Head of the National Timing Centre programme is Dr Leon Lobo. He explains how there are 80 or so laboratories around the world, similar to his, that provide the data humanity needs to coordinate the primary time standard regulating all our clocks and time. The result is what’s known as UTC, or Coordinated Universal Time. This is what we, in the UK and many Commonwealth countries, often call Greenwich Mean Time. (Confusingly, UTC is an abbreviation resulting from a compromise between English speakers who proposed the abbreviation CUT, for coordinated universal time, and French speakers who favoured TUC, for temps universel coordonné.)

Lobo explains how the National Timing Centre programme, which has received £36 million in government funding, is a response to the digital revolution currently engulfing our world. Many aspects of British industry and society need increasingly accurate timing to function properly.

Sunset and sunrise are displayed beside locks on the River Thames at Teddington. While for most ...

Sunset and sunrise are displayed beside locks on the River Thames at Teddington. While for most of us clocks of this accuracy suffice, increasingly internationally aligned technologies that deal in ever-finer shaves of a second require rather more. 

Photograph by Julia Gavin, Alamy

City of London trading is the first example that Lobo cites. The time margins used here are unfeasibly fine: one second for voice trading, one millisecond for electronic trading, and just 100 micro-seconds for high-frequency trading – all coordinated to UTC. If information flowing between different trading markets is all marked with indisputable time stamps, then traders can guarantee an international consistency, leading to more stable markets. It’s also a way of combating market fraud.

The energy sector is another example. Precise timing is needed to synchronise energy providers such as wind farms or nuclear power stations so that they can supply consistent power to the national grid.

Then there’s the broadcasting industry, which relies heavily on time-synchronised networks. Lobo explains how just the slightest anomaly can disrupt TV and radio networks. He points to an incident on January 26th 2016 when a decommissioned American satellite caused GPS receivers across Europe to skip by just 13 microseconds (that’s 13 millionths of a second), resulting in garbled digital radio services for several hours.

Sundials - such as this restored, early Christian period sundial at Nendrum Monastery, off the coast ...

Sundials - such as this restored, early Christian period sundial at Nendrum Monastery, off the coast of County Down, Ireland – were key to early timekeeping, and were often found in religious settings to keep track of prayer times. 

Photograph by David Lyons, Alamy

Lobo warns how GPS signals in general are vulnerable to jamming, and are a common tool of thieves. Devices used for this jamming are sometimes strong enough to disrupt entire city blocks. Alternative timekeeping sources will prevent that happening. They will also help future technologies such as 5G and autonomous vehicles by allowing roadside devices to receive signals directly from the National Timing Centre rather than via satellites orbiting the Earth. As the incident in 2016 proved, our satellite network is vulnerable to disruption.

A brief history of time(keeping)

It’s only in humanity’s recent history that timekeeping has been necessary at all. For the lion’s share of our time on Earth we relied on the Sun and the Moon to mark the passing of time. It wasn’t until we stopped hunting and gathering, and settled into farming communities, that a temporal division of the day was even necessary. From then on, for centuries, sundials, water clocks, candle clocks and hourglasses kept us ticking along.

In Europe, during the Middle Ages, as the church began to insist on strict prayer times, and a burgeoning mercantile class demanded a common standard for trading, clockmakers started upping their game. Very soon, mechanical clocks were chiming from churches and town squares all over the continent.    

From the 17th Century onwards there was a rapid advancement in timekeeping, spurred on by the Industrial Revolution, the expanding rail network and international marine trade: first the pendulum clock, then pocket watches, marine chronometers and, by the 20th century, quartz timepieces.

Finally, it was at NPL, in 1955, that two British physicists, Louis Essen and Jack Parry, constructed the world’s first accurate atomic clock – a caesium-beam version. “The death of the astronomical second and the birth of atomic time,” is how Essen described it. (The Americans had developed an experimental atomic clock six years previously, but a far less accurate one.)

Which brings us neatly back to the timing and frequency work taking place today in the very same laboratories at NPL. Alongside the National Timing Centre programme, work continues on the new generation of optical atomic clocks; the ones accurate to one billionth of a second per year. 

Louis Essen (left) and John Parry with the first working atomic clock in 1955. The device led ...

Louis Essen (left) and John Parry with the first working atomic clock in 1955. The device led to the redefinition of the second and the move from solar to atomic time.

Photograph by National Physical Laboratory / NPL

Lobo believes that if research is successful, backed up by similar research at other laboratories around the world, a new timing system could soon be adopted globally. He believes the new optical atomic clocks will eventually replace the base unit of time: what’s known as the SI second (from the French phrase ‘système international’), part of the International System of Units.

Such staggeringly precise timing has unearthed some unexpected side effects. The optical atomic clocks are so sensitive that their frequency changes when they are raised or lowered in height by as little as one centimetre. “It’s opening up new applications: not just timekeeping but measuring gravity potential,” says Lobo.

There is also a more humanitarian application. In order to check the stability and accuracy of their clocks, NPL compare them to similar atomic clocks in other laboratories around the world by sending signals down fibre optic cables over long distances. Many of these cables run along the sea bed where, it turns out, they are perfectly positioned to listen out for subsea earthquakes through variations in their signal frequencies. Lobo hopes that one day seismologists may be able to use this information to save lives by predicting tsunamis more quickly and accurately.

A life of such meticulous timekeeping should make Dr Lobo himself a punctual person, you’d imagine. Not so, it seems. “I’d say I’m average at timekeeping,” he says, revealing a flashy Rolex timepiece on his wrist. “But if I’m late, I can tell you exactly how late I am.”

Dominic Bliss is a freelance journalist based in London. Follow him on Twitter


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