The atomic clock

---

---

EU ES FR

EN CA GA

---

Partekatu

We need to talk about time and atoms below. How can the smallest parts of matter be able to measure minutes and seconds with incredible precision? This happens through atomic clocks, and, as strange as it may seem, these special clocks can be found behind many of the actions of everyday life. We met with a German professor to find out more; Robert Wynands is a reference in the measurement of time by atoms around the world.

ATOMIC CLOCKS We

know what time is: it’s a familiar, common thing. But try to define: what is time? For centuries, the definition of time has created more than a puzzle for scientists. Perhaps

the most practical solution was offered by Einstein: “Time is what we measure with the clock,” he said. That is, to limit time, we must resort to clocks. And if Einstein says so, it will be: we absolutely need the precision of the watches.

The most accurate clocks in the world are atomic clocks. They are needed to provide a world-class time infrastructure for GPS systems, financial transactions and/or telephony networks, among other things. Atomic clocks are special because they operate through oscillations of atoms; although there are many types, the most accurate ones are only nine in the

world.

Professor Robert Wynands is an expert in atomic clocks. He works at the German Metrology Center. In this institution, in addition to setting the official time in Germany, they have one of the most accurate atomic clocks in the world

in their facilities. ROBERT WYNANDS; GERMAN METROLOGY CENTER: It is very easy to explain how an atomic clock works: it works like any other clock. It has a system that works in a repetitive way: imagine a pendulum that goes back and forth. If you know how long a period lasts, just count the number of periods and then you will know how much time has passed. In an atomic clock there is not a pendulum in motion back and forth, but the oscillation within an atom, which we perceive with a technical system. It is precisely this technical system that is called the atomic clock.

Thanks to the radio signals sent by the atomic clock of the German Metrology Center during the day, there are already on the market some home clocks that have the power to receive this signal and then place the clocks automatically.

ROBERT WYNANDS; GERMAN METROLOGY CENTER: We have a long-wave radio transmitter that transmits information to millions of users throughout Germany. This signal can also be received here in Bilbao. It can therefore be said that we are providing time for the whole of Europe.

The most accurate clock in the world is at the Paris Observatory, which takes 80 million years to delay a second. This means that since the disappearance of the dinosaurs on Earth, it has had an error of approximately one second. In contrast, for the GPS system to function properly, satellites need atomic clocks that ensure that the error is at most 1 second in 32,000 years.

Satellite clocks in navigation systems look like a cylindrical shell, but inside they’re dancing atoms. The rhythm of this dance is really regular, and it is the source of the precision

of the watches. In the clock, the atoms are passed through a long tunnel where they are ordered before reaching a large cavity. There, they move in all directions. They excite the atoms and emit microwave photons. The frequency of these emissions is completely stable, always the same, and it is this regularity that generates the atomic rhythm, which is essential for any navigation system. These pulses are converted into signals and sent to Earth with a metronomic rhythm.

ROBERT WYNANDS; GERMAN METROLOGY CENTER: The interval between two “beeps” of atomic clocks is exactly the same as the interval between two “beeps” of universal time. But, from time to time, due to the speed of the Earth, we have to stop the clocks of our universal time—that is, our daily clocks—for a second. In this way, we will allow the Earth to assume a certain angle of rotation and we will be able to move forward. This is called inserting an additional second.

Due to the internal oscillation of the Earth, every two or three years, atomic time and universal or ordinary time are separated by one second. That’s why this year’s New Year’s Eve will be one more second for the celebrations, as the bells of the year 2.009 will arrive a second later than usual.

But beyond the anecdotes, important studies on atomic clocks are also being developed in recent years.

ROBERT WYNANDS; GERMAN METROLOGY CENTER: We compare atomic clocks of different types every year, and if we find any difference in the reading of clocks, it can be interpreted as a change in the numerical value of the fundamental constants. And I have to say that I find that absolutely shocking. By building clocks, I can learn to some extent how the world works: whether the constants of nature really don’t change, whether they are really constant.

Will it be possible to build more precise watches? Because we're talking about a second of accuracy in millions of years, and it's really hard to measure and improve that. Time will tell; the same thing that is measured with watches.