Tempus fugit . Since the dawn of humanity, we have regulated our rhythms and behaviors to the beat of the Earth itself, and in turn, the human species has tried to create tools and, later, technology capable of measuring with the greatest possible precision the cyclical activity of the Earth. space-time that surrounds us.
To this day, mankind has achieved the most accurate watch that has ever been created. But it is not how you imagine it: it is a cube of quantum gas.
To understand it, let’s analyze what has been the most accurate watch achieved so far. It was created in 2015, and it was extremely accurate: less than a second in 15 billion years (much more than the age of the universe, 13.8 billion years). It was also designed from strontium atoms.
Previous atomic clocks were created with cesium atoms , which were considered quite accurate: in them, the calculation of time is based on how long the energy changes of the electrons in the atoms last. Each change is a cycle, and a second is officially considered about nine billion cycles of a cesium atom.
Now, the new atomic clock of strontium atoms, designed by a team at the University of Colorado and led by scientist Jun Ye, has a much higher precision than the clock of 2015: If we put it to work in year zero , it would be ticking in a stable way and without deviating for a thousand times the age of the universe.
It works like this: the scientists arranged the strontium atoms in a lattice pattern and then stacked them into towers, in a three-dimensional structure, much more efficiently than the cesium atoms were previously placed: specifically, ten million of atoms per cubic centimeter.
How do these types of clocks measure time?
The tick-tock is measured by microwaves emitted by the electrons around the atoms , which jump from a lower orbit to a higher one, as they absorb and then lose energy from a laser.
And what was wrong with cesium atom clocks?
The truth is that the precision with which cesium electrons can measure time has a speed limit: they can jump back and forth ‘only’ nine billion times per second. The electrons in strontium atoms, on the other hand, can transit almost a million million times per second.
Thus, in the new watch, the 3D structure in which they grouped the strontium atoms allowed them to measure signals from more atoms at the same time within the width of the laser beam : ten trillion atoms per cubic centimeter compared to previous clocks, with ten billion atoms per cubic centimeter.
In addition, the researchers cooled the atoms to -273 degrees Celsius (the physically achievable limit or ‘absolute zero’) and trapped them in a fixed location to monitor interactions between them. “Imagine a scenario where you have a one-person house on a city block. One person lives in each house and neighbors are never allowed inside,” Ye explains. “Each atom fits into a particular place.”
Image: A blue laser beam excites a cube-shaped cloud of strontium atoms / GE Marti / JILA
Ultra-low temperatures turn atoms into what is known as quantum gas . “When the atoms are in the gas phase they are very hot, they are separating and colliding with each other,” he says. “This changes when the temperature of the gas is lowered, so much so that these particles start to move like waves, avoiding each other.”
And, all this, results in the most accurate clock in the world : it would only slow down three and a half times out of every ten quintillion; or, what is the same, only four tics out of ten raised to nineteen.
What is such an extremely accurate watch for?
Having clocks that are not delayed even a second in time, since the universe was formed, is vital to test theories such as Einstein’s General Relativity. In addition, clocks of such enormous precision, which remain accurate for billions of years, can have many different applications: in meteorology, radio astronomy, and form the basis of GPS.
Reference:
WB Cairncross, Gresh, DN, Grau, M., Cossel, KC, Roussy, TS, Ni, Y., Zhou, Y., Ye, J., and Cornell, EA, “Precision Measurement of the Electron’s Electric Dipole Moment Using Trapped Molecular Ions ”, Physical Review Letters, vol. 119, no. 15, p. 153001, 2017.
