Rare earth elements can help redefine time

What is '1 second'? Is it exactly the same as we think?

In a brief second, we can do a lot of things: recognize the acquaintance, snap your fingers, feel love, sleepiness or sneezing. Right now, the world's most accurate time clocks are about a second slow after 300 million years - so a clock that has been operating since dinosaurs so far will have no errors. But scientists believe we can do better than that.

New hope is being placed on Lutetium, the long-forgotten, rare earth element, located at the bottom corner of the periodic table. New research has been published April 25 in Nature Communications.

Why is a second not a second?

In the past, a second was defined as a very small part (1/86400) of a normal solar day, when the Earth rotated a full circle (24 hours) around its axis. But due to many reasons, this rotation may change (for example, in the 2004 Indian Ocean earthquake and tsunami, the earth was spinning faster than about 3 microseconds), so scientists decided stop using the sun to calibrate the clock and shrink everything down - to the atomic level, which cannot be observed with the naked eye.

In 1967, the International Commission for Mass and Measurement (CIPM) defined '1 second' as the time required for a Cesium (Cs) atom to absorb enough energy to be excited - ie the electrons of it moves from the existing energy state to the next energy state. In other words, cesium atom converts between two 9,192,631,770 energy states, which is counted as 1 second. This measurement takes up to three years to complete, according to American Scientific Journal.

Researchers next to cesium atomic clock code NIST-7.Located in Gaithersburg, Maryland, this timepiece was responsible for measuring time in the US from 1993 to 1999, but was later replaced by another more accurate cesium watch.Photo: American National Institute of Standards and Technology.

Today, hundreds of cesium atomic clocks are responsible for maintaining global time and controlling GPS navigation systems. But in the past decade or so, another generation of atomic clocks has emerged. Called, they are 100 times more accurate than the old ones. Operating on the same principle as a cesium clock, they use aluminum or Ytterbi atoms excited by the higher frequency of visible light (hence the name "optical") rather than the microwave cycle. Slower.

Compared to 9,192,631,770 - 9.1 billion times the oscillation cycle of cesium ion, the oscillation cycle of Ytterbi ions is 1.6 x 1,000,000,000,000,000,000 - 1.6 billion times, the figure published in 2013. This superiority adds Add more data to the definition of "seconds" , making it more accurate. 'Imagine two types of watches like a pair of rulers , ' says Murray Barrett, a professor of physics at the National University of Singapore and a new researcher. 'If cesium is measured in centimeters, the new' optical 'ruler can be more accurate than a millimeter,' he said.

currently taking real-time measurement in the US, is one of the most accurate clocks in the world.(Photo: NIST).

While optical clocks have very high accuracy, having them work for a long time and can constantly raise problems, according to Professor Barrett. The high ambient clock temperature will affect the electromagnetic field acting on the atom, and can distort the measurement time. So he told Live Science that cesium watches are still "much more reliable in measuring than new optical clocks".

Increase inertness for atomic clocks

In his new announcement, Professor Barrett and his team discovered that a Lutetium ion is less sensitive to ambient temperature than any other element used in previous optical clocks.

Lutetium atoms also help compensate for another problem affecting time measurement, according to the research team. Because the atoms used in these clocks are 'charged', they oscillate back and forth in response to electromagnetic waves generated by waves (visible light, microwaves, etc.) - and this may deviate the measurement time.

Scientists have long had to compensate for this change, but the team found that a type of Lutetium ion has the property of eliminating those 'micro-movements'. However, the Lutetium ion type mentioned above becomes sensitive to ambient temperature, so new discoveries are still unable to 'change the rules of the game', according to Jérôme Lodewyck, a physics expert at the Paris Observatory.

Beyond the time category

According to Professor Barrett, high-precision optical clocks have applications that "are not possible with our current technology."

For example, the sensitivity of the clock changes according to its position in the world, because time is distorted by gravity according to Albert Einstein's general theory of relativity. Currently, atomic clocks cannot detect time warping due to gravity. But if researchers can place multiple optical clocks around the world, that network will help map out the gravitational field of our planet.

Moreover, high-precision optical clocks can detect matter and energy that we don't see, according to Lodewyck. Specifically, dark matter, which creates gravity but does not interact with ordinary light and dark energy, mysterious power seems to accelerate the expansion of the universe, he said. How to do the following: If you know the frequency fluctuates enough to excite a specified number of atoms in a time frame of 1 second, you can use multiple clocks around the world to detect anomalies. Some theories suggest that dark matter is somewhere around us, so 'if you cross a dark matter area, it will interfere with the clock' , Lodewyck said.

There are even applications that we can't think of right away, Barrett said."When developing clocks to navigate ships, we never envisioned the idea of ​​using it to determine where we are moving in a big city."