How big is an atomic clock

Modern timesIn time with the atomic clock

Ekkehard Peik: "We are now entering a room in which there is no radio or cell phone reception."

Walls completely lined with copper.

"This was done to ensure that the clocks did not interfere with the outside world."

A room the size of a gym. The inventory: various atomic clocks, including the best prototypes in the world. Your accuracy: enormous. Your mistake: minimal.

Ekkehard Peik: "Less than a second over the age of the universe, that's about 13.8 billion years."

Next generation timepiece, almost perfect. They are already waiting to be used in the laboratories. How will they change our world, permeate everyday life, determine life?

Günther Oestmann: "The first clocks were elementary clocks. Usually water clocks, sundials. In the oriental area through controlled burning of incense sticks and the like."

Man measures time. Since time immemorial.

"We know from the large number of public timekeepers, be it sundials or water clocks in the Roman Empire, that timekeeping definitely played a role in public life."

Time shapes people. Since time immemorial.

"If the sundial is constructed correctly, you can easily read ten-minute intervals."

Always more precise. Always more precise. Always faster.

The makers of the time sit at PTB

"We are here in PTB's atomic clock hall. I believe it is unique that we have these different types of atomic clocks together in one laboratory."

Ekkehard Peik, Physikalisch-Technische Bundesanstalt, Braunschweig. Here, at PTB, are the makers of the time. Tomorrow's. And the one of today: the Casium atomic age.

The clocks: lasers, gauges, electronics cabinets. Empty pumped metal barrels, inside clouds of atoms - cesium, laser-cooled:

"You radiate microwave radiation on the cesium atoms, look: How does the cesium react to it? Does one hit its resonance frequency? So that the clock oscillates afterwards at the frequency of the cesium atom."

The second: 9,192,631,770 times the frequency of the cesium atom.

"An uncertainty in the range of ten to the sixteen."

The mistake: only one second in 100 million years. That is the accuracy of our official time.

"These clocks run continuously and serve as an output signal for the time services that we distribute."

Telephone, radio, internet, satellite: this is how atomic time comes to the outside, synchronizing traffic, factory buildings, everyday life.

"A total of almost 500 clocks contribute to world time."

The result: the world time. Since 1967, for 50 years, the meter of the earth.

"UTC, an English abbreviation: Universal Time Coordinated."

Time runs steadfastly, with stoic precision. But the earth rotates unsteadily. Sometimes faster, then slower.

"If necessary, leap seconds are inserted to keep UTC in agreement with the earth's position. This is irregular, on average about every one and a half to two years."

The last leap second: Last night at 11 p.m., 59 minutes, 60 seconds.

A look back at history: the European Middle Ages

The Antikythera Mechanism, a non-functioning, incompletely preserved find with 82 fragments from antiquity with a multitude of cogwheels in a similar arrangement to a clock, in the National Archaeological Museum of Athens (imago / ANE Edition)

"The next step is the development of the clock at the end of the 13th century."

Günther Oestmann, lecturer in the history of science, TU Berlin.

"An important moment was certainly the time measurement in the monastery area. In the Benedictine order in particular, the times of prayer played a dominant role. This is where the first alarm clock-like mechanisms emerged."

The drive: a weight that sags downwards. Gears mesh with each other. A spindle inhibits the urge, divides the flow of time into a constant cycle.

"This escapement was a revolutionary step. But the clocks were relatively imprecise. A weight-operated spindle clock could deviate by up to an hour a day.

The clock face did not play the dominant role at first. The bell signals were important in a city. These bell signals not only coordinated services and prayer times, but also other urban activities. For example, there was a so-called mus-bell for public meals. Time was communicated through such signals. "

The strike of the clock organizes the medieval city.

"The introduction of the pendulum clock represented a revolution in accuracy."

A pendulum swings exactly once per second - if it's the right length.

"This was associated with a considerable increase in accuracy. The first pendulum clocks were able to achieve accuracies in the range of ten seconds per day, which was unbelievable for the conditions at the time."

The atomic clock business

Christoph Affolderbach: "Historically, this is where the Jura Arc in Switzerland is - one of the strongholds of the Swiss watch industry."

Neuchâtel in Switzerland. A city where accuracy is a tradition: generations of watchmakers once had their chronometers calibrated at the Neuchâtel observatory. This tradition has saved the city into the modern age.

"Here in Neuchâtel we have two large European companies that manufacture atomic clocks. The global market is tens of thousands a year."

Atomic clocks can be bought. The military need them to navigate submarines and drones. Oil companies use them to search for new deposits. And: atomic clocks are the basis of GPS. On board the satellites, they deliver ultra-precise time signals that are transmitted to earth and used there by smartphones and GPS receivers for navigation.

Most atomic clocks, however, can be found elsewhere: compact, relatively inexpensive models. They are in fiber optic lines and cellular networks, the lifelines of the digital world, explains Christoph Affolderbach:

"The trend in telecommunications and the Internet is that more and more data should be transmitted at higher speeds and shorter times. To do this, you have to synchronize the clock of the sender with the clock of the receiver. For this you need atomic clocks that set a constant clock. "

The atomic clocks are built into the nodes of the telecommunication networks. There is one in almost every district. These atomic clocks are hardly bigger than a packet of cigarettes and hardly more than 1000 euros. If they were even smaller, more robust and cheaper, they could be stuck in every cell phone mast:

"That would simply have the advantage that you could achieve a higher data transfer rate. Up to the mast, you could enable higher data traffic."

Christoph Affolderbach is working on miniature atomic clocks like this in Neuchâtel:

"This is our big laboratory where I work on the highly compact vapor cell atomic clocks."

Laser equipment and test stands, separated by curtains.

"All of these research projects use laser diodes as light sources. To shield the light from interfering light from another experiment, we use these black theater curtains - simply to protect the experiments from each other."

Affolderbach is now taking something from the laboratory bench - a cylinder made of silicon, the lid and bottom are made of glass. The dimensions: quite small.

"Two grains of rice next to each other."

The core of a highly compact atomic clock.

"Rubidium droplets are trapped there. Above these droplets, which are liquid metal, a vapor of rubidium atoms forms, like a fog that forms over a warm lake on a cold winter's day. We use this fog as a reference for the atomic clock. "

Two beams are directed into this nebula: Lasers prepare the atoms, microwaves read their frequency.

"Not far from the microwave frequency that is used in the kitchen in the microwave."

Atomic clock for everyone?

The core piece is the rice grain-sized silicon capsule, plus a laser, microwave generator, electronics for control and evaluation. The complete atomic clock is only slightly larger than a matchbox.

"Here you can see the watch prototype from our Quantime project. The diode laser sits on the front," says Affolderbach. "It's only a tenth of a millimeter in size, you can't see it with the naked eye. You have to use the magnifying glass to help."

Some time ago, the US company Microsemi brought a similarly compact atomic clock onto the market, weighing 35 grams, which a London watchmaker named Richard Hoptroff has now built into a wristwatch. Starting at £ 12,000 each, a status item. A rather bulky model, but the most accurate wristwatch in the world: In a millennium, it only goes wrong by a second - and practically never has to be set.

Reliability is the primary quality of an atomic clock. Much more, however, something else counts: With atomic clocks, tiny time intervals can be measured, controlled and tamed: the back and forth of data packets in the cell phone network. The sequence of light pulses in fiber optic cables. And a tiny tremor in the power grid.

"The problem arises from the fact that energy is fed in at many points in the network with renewable energy sources. This leads to increased instability of the distribution network. If these energy networks run out of phase, you get problems switching the high-voltage network, which leads to costly damage can. "

Atomic clocks in the switching points synchronize the energy flows. Their cycle keeps the power grid stable even when more and more wind turbines and solar cells feed in their energy. The smaller the clocks get, the more you will start with them. An atomic clock the size of a sugar cube is not science fiction, says Christoph Affolderbach:

"But it is hard work to actually make it happen. The dream would of course be to be able to realize an atomic clock directly as an electronic component. In theory, that could be possible. But the way there is still a long way.

The atomic clock as a microchip, that is the distant vision of the professional world. The atomic clock for everyone.

"There you can dream that if the clock is sufficiently small and inexpensive, it can be built into laptops, PCs, cell phones or into GPS receivers. The benefit could be that a higher data transfer rate could be made possible. For applications in GPS receivers it could be achieved that the duty cycle until the device is operational could be reduced significantly. "

Atomic clock in the Bose-Einstein condensate

Cells the size of a pinhead filled with a vapor of atoms. That is the approach taken by Affolderbach and his people. Others are working on an alternative concept - the atomic clock on the chip:

"What was only possible in the past with large magnetic coils, something that, let's say, took up space on a dining table, can now be done on a two by two centimeter surface," explains Tommaso Calarco, physicist at Ulm University.

For some time now there have been chips the size of postage stamps that act as atomic traps: electrical currents flow on their surface and build magnetic cages - cages in which atomic clouds can be locked up. For a miniature atomic clock, these atomic clouds would have to be cooled extremely well. This is the only way they take on a special state of matter, called Bose-Einstein condensate:

"There are millions of atoms in the same quantum state at zero temperature. When we have such states - they are even more sensitive to the passage of time than the non-ultra-cold ones. We are in very precise states that allow us to measure our time even more precisely."

The preliminary work has been done. Several groups in the laboratory have already succeeded in creating a condensate on a chip. Now they are trying to make a clock out of it. One of the challenges: The lasers that cool and control the ultra-cold cloud have to be made much smaller:

"There's a clear way of doing that."

A look back at history: overseas trade and industrialization

John Harrison's Chronometer in the Immigration Museum, Ellis Island, New York (imago / Anka Agency International)

Günther Oestmann: "There was a need. With the expansion of overseas trade, this problem became urgent."

The 18th century. Ships conquer the globe. They don't always find their way.

"It would be very useful to have a watch that reliably shows the time of the port of departure, so that you can determine the length from the time difference at sea."

When the sun is at its highest, the crew knows: It's 12 noon on board. Then the clock comparison follows: A clock on the ship shows what time it is in the port of departure. The calculation is simple: if it is at 1 p.m., you are 15 degrees away. If it is at 3 p.m., it is 45 degrees of longitude, namely to the west.

"The breakthrough came in the 18th century with John Harrison."

A brilliant designer. Conditions on the high seas are harsh - Harrison's chronometer can withstand them. The acid test followed in 1762: a trip to Jamaica for eleven and a half weeks. The rate deviation: minimal.

"It was only a few seconds. It was so incredibly precise that the commission that had to assess it at first became suspicious and demanded further checks."

James Cook travels the South Seas - and praises the watch as a never-failing guide. The longitude problem is solved. What follows is the measurement of the world.

"In Switzerland the first attempts were made to bring timepieces onto the market cheaply in mass production."

Time is industrialized.

"You can say that at the end of the 19th century many people owned a watch - be it a simple alarm clock, be it simple pocket watches."

Time for everyone, time for everyone. The basis for structure, punctuality, stress.

"This is really a general chronological cycle of life that you can perceive in the 19th century. This is the only way to synchronize activities and schedule appointments."

Atomic clocks for financial jugglers

Leon Lobo from the National Physical Laboratory (NPL) in London in front of an atomic clock (Frank Grotelüschen)

"In the rooms where our best atomic clocks are located, the temperature is kept constant to within a tenth of a degree," says Leon Lobo. "If someone comes into a room like this, he influences his temperature through his body heat - and thus the running of the clocks. That is why we avoid entering these rooms. We practically never go into some rooms."

Teddington in south west London. Here you can find the British variant of PTB - the NPL, the National Physical Laboratory. A place with tradition: the world's first cesium clock was built here in 1955.

Physicist Leon Lobo opens the door to a small, windowless room full of technical equipment:

"Cabinets with lots of electronics: cesium clocks, distribution systems, measuring devices and apparatus that feed our high-precision time signals into glass fibers."

Lobo now points to one of the electronics cabinets. Flashing LEDs at the front, fiber optics branching off at the back.

"This is where the signal is generated. At the other end of the glass fiber there are similar devices. They receive the time signal and pass it on to the customers."

The customers are located 25 kilometers away - the banks in the City, the financial district of London. A hub of international high-frequency trading.

"It has always been a race that was about processing more and more data in ever shorter times. And this race will go on, it won't stop."

It is not flesh and blood brokers who make decisions, but computers. You buy and sell in a split second.

"High frequency trading is a part of the financial market where computer algorithms trade large amounts of securities at extreme speeds."

Proponents say: High-frequency trading ensures more liquidity in the market and thus better prices. The critics say: High-frequency trading is of no use to society and endangers the stability of our economy. One thing is clear: there are difficulties and they are of a technical nature.

"This type of trading has gotten faster and faster - so fast that regulators can hardly keep track of who did what when."

Every automatic transaction has a time stamp. The computer that sends a transaction gives it an exit stamp. The computer that receives this transaction puts an entry stamp on it. The problem:

"Every bank gets its time from a different source, a different clock - some via GPS, others via the Internet. As a result, the transactions have different time stamps. And it can happen that the second stamp shows an earlier time than the first. Then it looks like the information arrived before it was even sent. "

Such a mishap occurred in 2013 to the media group Thomson Reuters.

"He released certain market data 15 milliseconds early. That time was enough for some of the algorithms to trade stocks for $ 28 million."

A distortion of competition, the regulatory authorities see a need for action. As of January 2018, they will tighten the regulations.

"From 2018 onwards, the players involved in high-frequency trading must provide their transactions with time stamps that do not differ from universal time by more than 100 microseconds."

A problem that arose from juggling with the smallest units of time, with milliseconds and microseconds. It should be solved by an even finer time grid, by even more precision - by the best atomic clocks in England.

"We use a fiber optic cable to the London financial district. We use it to send the high-precision signals from our atomic clocks. The banks no longer work with any time. They work with time."

Sophisticated control systems ensure that the entire signal chain in the bank functions precisely enough - right down to the time stamp that marks the transactions. In 2015, Lobo and his colleagues started a long-term trial with the UBS London branch. The physicist believes that the system is now ready for use. But doesn't his work ultimately contribute to making high-frequency trading even faster - and thus even more risky?

"No, not at all. It's not about further accelerating high-frequency trading. No - our method, our more precise time measurement, helps to better understand what is happening in the automatic transactions in detail and thus creates more breakdown security and transparency."

A look back at history: from Greenwich to the modern PC

Günther Oestmann: "In England there were competing railway companies that had different times. Accidents then quickly occurred due to different time systems."

The time is standardized. From 1884, Greenwich Mean Time applies - the zero hour of world time.

"Up until then you had different local times, local times. They have marked time differences. This became noticeable with the railroad, and it proved necessary to coordinate times between the locations."

Experts divide the world into time zones. Time is becoming international.

"The next leap was the development of the quartz watch in the early 1930s."

A quartz crystal under tension, the crystal lattice oscillates. A microscopic pendulum, constant and highly accurate.

"The quartz watch was still very expensive. It was not until the 1960s that the quartz watch was further developed for industrial series production."

The quartz watch on your wrist. And: the quartz in the processor, the clock in the PC. Fast computers would be unthinkable without him.

"Small quartz clocks are built into computers. Of course, they have also been miniaturized."

Megahertz, gigahertz. The rhythm of the digital revolution.

Optical atomic clocks are said to be a hundred times more accurate than cesium clocks

"Every one to one and a half seconds we load a new cloud of strontium atoms, compare the frequency of the laser with the atomic frequency and load a new cloud of atoms."

The PTB in Braunschweig. The physicist Christian Lisdat stands in a darkened laboratory room in front of a massive table top with a labyrinth of mirrors, screens and sparkling laser beams.

"Cold atoms are being created and trapped here. You can tell that the blue light is on for a while and then switched off. It clicks here because a mechanical shutter is being operated."

Lisdat and his team are working on the time measurement of the future - the optical atomic clock. A clock a hundred times more accurate than the best cesium clocks.

"The key difference is that we significantly increase the frequency of the pendulum oscillation, by a factor of more than 10,000. If you have a pendulum that swings faster, it allows you to measure more precise time intervals."

Optical clocks, for example, are based on strontium atoms. They vibrate in the optical frequency range, so much faster than today's cesium clocks with their microwave frequencies. There are already prototypes - but they are not yet stable enough. Christian Lisdat wants to make the new super watches transportable - and thus suitable for technology.

"Now we're out here in the parking lot in front of our laboratory building. And in the parking lot is our trailer with our portable watch."

Christian Lisdat in the laboratory of the Physikalisch-Technische Bundesanstalt behind an optical clock. One day, optical clocks could replace the cesium atomic clocks. (Julian Stratenschulte / dpa picture alliance)

Lasers, glass fiber optics, vacuum systems, control electronics, measuring computers - everything is packed into five square meters of loading space. And it could be even smaller.

"The first step would be to leave the experimenters at home and leave out all the space for them. Then we would be with a structure that is somewhere around a cubic meter."

Christian Lisdat's vision:

"Sending optical clocks to satellites is our plan. We are in the process of building prototypes and exploring how big such a system can be and how much energy it would consume."

Outlook into the future: from parcel carriers and killer robots

In 2015, researchers tested the components of an optical clock for the first time under weightlessness, for a few minutes on a parabolic flight. In a few years, a prototype is to be tested on the international space station - then for a longer period of time.

"If the technology is there, it will probably find its way in the direction of satellite navigation systems," says Christian Lisdat.

Today the GPS satellites have cesium clocks on board. An optical watch is a hundred times more precise. With them, GPS receivers can determine their position down to a centimeter instead of the previous meter. A technological leap for machine navigation is on the horizon: Drones that deliver targeted parcels - or spy with pinpoint accuracy. Robots that provide first aid in the right place - or kill in urban warfare. Geoscientists will also use optical clocks: to precisely record height differences.

"First of all, this is a surprising effect that comes from the general theory of relativity - namely that the speed with which time passes depends on where I am in the earth's gravitational field. This effect can, in principle, be used to reduce height differences to be determined very precisely. "

A clock on a mountain ticks faster than one in the valley. A phenomenon that the Braunschweig locals have already observed: They parked their car trailer with an optical clock in a tunnel in the Italian Alps. Then they compared the signal using a fiber optic cable with a clock in the valley - and were actually able to determine the altitude.

"We got a few meters exactly."

Too imprecise for technical revolutions. But:

"For the first attempt, we were quite satisfied that the clock worked at all. It was a demonstration experiment."

Now Lisdat is aiming for a precision of centimeters - and the exact measurement of the globe in the vertical: How fast is the sea level rising? How does the earth rise and fall in quake-prone regions?

The days of the cesium clock seem numbered

Soon only to be found in the museum? The inner workings of a cesium clock (Frank Grotelüschen)

Our processes run faster and faster, we need a new cycle. The age of the cesium clock lasted 50 years, now its days seem to be numbered. The optical atomic clock will soon be the measure of all things. It promises us a new second, more precisely defined than ever before.

"That will definitely be done," says Ekkehard Peik from PTB. "I think, however, that it will take its time because research in this field is still going so fast that it is not at all clear which atom would be best suited."

Some rely on strontium. Others on ytterbium or aluminum. Still others on calcium. All the prototypes are not yet reliable enough. But the researchers will get that under control, of that they are sure. Ekkehard Peik:

"You should wait for this development to be able to make a really good decision that will last for a long time."

Speakers: Jennifer Güzel, Andreas Neumann and Clemens Nicol
Technology: Birgit Vetter
Director: Frank Halbach
Editor: Christiane Knoll
Online: Felix von Massenbach

A production by Deutschlandfunk 2017