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Why It’s Time To Redefine What A Second Is (And What Mysteries Of The Universe It Would Help Us Unravel)

Do you have a minute to talk about the second one?

The fundamental measure of timeon which most of the other magnitudes in our measurement system depend, has not changed for more than 70 years.

The advancement of technology, however, indicates that it is time to update the definition of what a second is, to make it more precise.

This is what the researchers at the International Bureau of Weights and Measures (BIPM, for its acronym in French), located in Paris, France, consider.

This body is responsible for establishing the standards in the world’s measured unit systems.

BIPM metrologists, together with experts in several countries, are preparing to change the way they measure a second.

It is a rather delicate operation, the result of which could be key to changing the way in which we understand the universe.

What is a second?

The second is the base unit for the measurement of time in the international system of measurements.

In fact, other base units such as the meter (length), the kilo (mass), the ampere (current), and the kelvin (temperature) are defined in terms of the second.

Thus, for example, the BIPM defines the meter as “the path traveled by light in a vacuum during a time of 1/299,792,458 of a second”.

For millennia, humanity has used astronomy to define its units of time.

But since 1967 the definition of the second is drawn from the observation of atoms.

That’s because atoms behave more precisely than the Earth’s rotation, which isn’t perfectly smooth.

Scientists have observed that for millions of years the Earth has been rotating slowercausing, on average, days to lengthen by 1.8 milliseconds every century.

Thus, for example, 600 million years ago, a day lasted just 21 hours.

And to top it off, in 2020 several studies showed that during the last 50 years the planet had started to spin faster.

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Atoms allow for more precise time measurement.

So, even if imperceptible, the “astronomical second” it is not always the same.

Atomic particles, on the other hand, move more accurate and predictable.

the second atomic

It was thus that since 1967 the second began to be defined based on the oscillation of particles of cesium atoms 133 when exposed to a special type of microwave.

The device responsible for making this measurement is known as atomic clock

Under these microwaves, the cesium 133 atoms behave like a pendulum that “swings” 9,192,631,770 every second.

At that time, the second that was taken as a reference to count the oscillations was based on the duration of a day in the year 1957, which had been determined from the behavior of the Earth, the Moon and the stars.

In this way, the BIPM established that the official measurement of the second would be defined from the number of oscillations of the cesium 133 atom particles.

Thus, in simple words, today the second is defined as the time it takes for the cesium to oscillate 9,192,631,770 times.

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A clock measuring ytterbium atoms at NIST.

the new second

But that definition seems to have its numbered days.

For nearly a decade there have been atomic Optical Clocks, they have the ability to observe the “tick tock” of atoms that oscillate much faster than cesium.

Some count the ticks of ytterbium, strontium, mercury, or aluminum, for example.

It is as if a magnifying glass were put on the atomic clock with which it manages to detect more oscillations, with which it can define the second with Greater precision.

In addition, today there are dozens of these optical clocks in several countries, which is expected, as some experiments have already shown, that the measurements they make between them can be compared, as a way of checking the results.

The BIPM plans to use optical atomic clocks to measure the second, but they are still working on criteria to make that measurement.

According to Petit, the most important thing is to check the accuracy that optical watches promise.

So far, the best optical watch comparisons have been between watches in the same lab.

The challenge, says Petit, is to compare several watches from different laboratories.

In addition, it is necessary to choose the element of the periodic table whose atom will be used as reference in cesium replacement.

Optical clock that measures strontium atoms.

Furthermore, optical atomic clocks are tremendously complex devices, many of them requiring an entire laboratory to operate.

Some of the challenges facing these devices are, for example, emitting exactly the right kind of laser light to make the atoms oscillate in the right way; or have ultra-fast laser pulses with minimal intervalsso that they do not miss the oscillations that they must count, as explained to the portal livescience researcher Jeffrey Sherman, from the Time and Frequency Division of the United States National Institute of Standards and Technology.

If everything goes according to plan, the criteria will begin to be defined in June and the new second should begin to be in force from 2030, according to what Gèrard Petit, a researcher from the BIPM Time team, tells BBC Mundo.

“They are operations and comparisons complex“, He says.

revealing mysteries

What will happen when the definition of the second changes?

“Any”says Petit laughing.


The main reason to update the second is keep things in order.

The world’s measurement structure depends on the second.

“For a while it is possible to live with a definition that is not the most precise, but after a while it becomes unintelligiblePetit says.

“In practice, in daily life, it may not change anything, but in science a definition is necessary that is based on the best possible measurement.

In addition, ultraprecise time measurement can help us understand hitherto misunderstood phenomena.

NIST explains, for example, that optical clocks have already been used to measure space-time distortion which describes Einstein’s theory of relativity.

Gravitational waves warp space-time.

Optical clocks are so precise that they can show a difference between two clocks that differ in elevation by just one centimeter.

That’s because due to gravity, time runs slower at sea level than it does at high altitudes like Mount Everest, for example.

These ultra-precise clocks could also be used to detect the enigmatic dark mattera component from which 25% of the universe is made but about which little is known.

With this technology, scientists could detect that “something” that influences ordinary matter and space-time.

And they could also give clues about the primordial gravitational waveswhich are echoes from the Big Bang that warp space-time, like a stone thrown into a lake.

Atomic clocks could be able to detect these deformations and give us more clues about the start of our universe.

Source: Elcomercio

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