Why it’s time to redefine what a second is – and what secrets of the universe it might reveal

The BIPM metrologists, along with experts from several countries, are preparing to change the second measurement method. It is a very delicate process, the outcome of which may be fundamental to changing the way we understand the universe.

The second is the basic unit of time measurement in the international system of measurement.

But in fact, other basic units such as the meter (length), kilogram (mass), ampere (current) and kelvin (temperature) are specified based on the second.

The BIPM defines a scale, for example, as “the path that light takes in a vacuum during a period of 1/299.792.458 of a second.”

For thousands of years, mankind has used astronomy to determine its time units. But since 1967, the observation of atoms has been used to define the second. That’s because the atoms behave more precisely than the Earth’s rotation, which is quite irregular.

Scientists note that over the course of millions of years, the Earth has been spinning more slowly. As a result, days are increasing at a rate of 1.8 milliseconds per century.

So, for example, 600 million years ago, an Earth day lasted only 21 hours. To make matters worse, several studies in 2020 show that in the past 50 years, the planet has started to spin faster.

So, while imperceptible, the “astronomical second” is not always the same, while atomic particles move more accurately and predictably.

Since 1967, the definition of the second began to be based on the oscillation of particles of 133 atoms of cesium, when exposed to a special type of microwave. The device used to make this measurement is called an atomic clock.

When exposed to these microwaves, cesium-133 atoms behave like a pendulum that “swings” 9,192,631,770 times per second.

Until then, the second used as a reference for calculating oscillations was based on a one-day duration in 1957, determined from the behavior of the Earth, Moon, and stars. Now, the BIPM has determined that the official scale of the second will be calculated from the amount of oscillations in the particles of cesium-133 atoms.

So, in a nutshell, the second day is defined as the time it takes cesium to fluctuate 9,192,631,770 times. But this definition appears to be outdated.

About a decade ago, there were optical atomic clocks, which had the ability to monitor the “sign” of atoms oscillating much faster than cesium.

Some count ytterbium, strontium, mercury, or aluminium, for example. It is as if an atomic clock has a magnifying glass that allows it to detect more oscillations and determine the second with greater accuracy.

Currently, there are dozens of such optical watches in different countries. It is expected with them, as some experiments have already shown, that different measurements can be compared to substantiate the results obtained.

The BIPM plans to use optical atomic clocks to measure the second, but it is still setting standards for making that measurement. The most important thing is to prove the accuracy with which the optical clocks promise, according to Gerard Petti, a researcher on the time team at the BIPM.

To date, the best comparisons of optical clocks have been made from the same laboratory. But Petit told BBC News Mundo, the BBC’s Spanish-language news service, that the goal was to compare different hours from different labs. It is also necessary to identify the element of the periodic table that will replace cesium as a reference.

Furthermore, optical atomic clocks are very complex devices, many of which require an entire laboratory to operate.

Some of the challenges with these devices are, for example, emitting some type of laser radiation with pinpoint accuracy to make atoms oscillate correctly, or having ultra-fast laser pulses with minimal time intervals, so as not to miss the oscillations that need to be calculated. , explains researcher Jeffrey Sherman, from the Department of Time and Attendance at the National Institute of Standards and Technology (NIST) to the Live Science portal.

Gerard Pettit points out that if all goes according to plan, setting standards should begin in June 2022, and a second standard should take effect from 2030.

“These are complex processes and comparisons,” he says.

What will happen when I change the definition of the second?

“Nothing,” Betty said with a laugh.

The main reason to update the second is to keep things in order, since the scaling structure of the world depends on the second.

“It is possible to live for a while with a definition that is not the most accurate, but after a while it becomes incomprehensible,” Pettit says.

“In practice, in everyday life, it probably doesn’t change anything, but in science, you need a definition based on the best possible measurement.”

In addition, ultra-accurate time measurement can help us understand phenomena that are not currently understood.

The National Institute of Standards and Technology (NIST), for example, explains that optical clocks were once used to measure the distortion of spacetime described by Einstein’s theory of relativity.

Light clocks are so accurate that they can show the difference between two hours with a difference of just one centimeter in height. This is because time, due to gravity, travels more slowly at sea level than at higher altitudes, such as Mount Everest, for example.

These ultra-precise clocks can also be used to detect the mysterious dark matter, which makes up 25% of the universe, but about which little is known. With the new technology, scientists will be able to discover this unknown substance that affects ordinary matter, space and time.

They can also provide clues about primordial gravitational waves, which are echoes of the Big Bang that enveloped spacetime, like a stone was thrown into a lake. Atomic clocks may be able to detect these distortions and provide more clues about the formation of the universe.

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