Summer time: ‘Timekeeper’ will sleep well next night and will check the atomic clock tomorrow morning

“Everyone thinks I should also put the four clocks forward an hour at 2 a.m., but I don’t really have to do much,” says the scientist, chuckling over the phone. This is because the atomic clocks do not keep track of the local Dutch time, but – the name says it all – the atomic time.

How that works? An atomic clock uses vibrations of atoms. They vibrate so evenly and constantly that there would be a deviation of one second at most once every 5 billion years. So extremely accurate. So an atomic clock always ticks quietly, like an endless metronome. That steady ticking is ideal for physicists to determine seconds, minutes and hours. And whether that is summer or winter time, or another time zone elsewhere in the world: an atomic clock just keeps ticking. “The atomic clock is the same all over the world and has no summer or winter time,” explains Dierikx.

So little work for Dierikx, but elsewhere in the country, because no one uses the atomic time in everyday life, but the local Dutch time, including summer time. “This means that we don’t have to move the atomic clocks in the VSL laboratory, but we do have to move the clocks that keep track of Dutch time, such as at home, on the street, on the church tower, and so on. In many mobile phones, computers and the like, this happens automatically.”

The only thing Dierikx checks is the clock of the German time transmitter DCF-77 from Mainflingen, near Frankfurt am Main. It sends out a time signal every second that is picked up by radio-controlled clocks in Germany, but also in the Netherlands, which therefore all run synchronously. “On the radio-controlled clock I have at home, I check whether the German broadcast clock has also switched from winter to summer time. I only do that on Sunday morning. Saturday night I slept through,” he says delighted.

What time experts such as Dierikx are fully occupied with is the leap second. Because we want the time to be not only extremely accurate, thanks to the atomic clock, but also to match the rotations of the earth: one revolution around the axis must be 24 hours, one revolution around the sun must take exactly one year. And that is not always true. Leap seconds, if necessary, equate our atomic clocks with the time measured by the Earth’s rotation.

Dierikx: ,,The rotation time of the earth is difficult to predict. In the past 50 years, we’ve had a leap second 37 times. Until now, those were positive seconds that we added because the Earth rotated more slowly, but in recent years we have seen an increase in rotational speed. That can lead to a negative leap second, which could cause major problems in, for example, computer systems that do not have such a negative second built in, unlike positive leap seconds. Although it is only one second, we are more awake about it than about the hours at the transition from summer to winter time.

As far as the national time manager is concerned, summer or winter time is being abolished, so that we keep the same time all year round. “In our 24-hour economy, changing the clock no longer has such an impact,” says Dierikx.

Moving the clock forward was introduced in 1977 because of the oil crisis. Making longer use of sunlight would save energy, was the reasoning. Now that this has no longer had such a great effect, since 2019 EU member states have been allowed to decide for themselves what time they want to use, provided they let us know in time to prevent practical problems. It has not yet led to adjustments, in various member states there is still discussion whether the current winter time or summer time should become the new standard.

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