Time is an essential part of our day-to-day activities, and keeping track of how an event progresses is why we have clocks around. The first clocks ever made dates back to medieval time, and there’s been so many modifications. Physicists have now developed an atomic clock so accurate that it would be off by less than a single second in 14 billion years. A clock with such accuracy and precision makes it so powerful a scientific instrument that it could measure more than just time, but the forces around it. Sounds too amazing to be true. How did they even do it? Let’s explain!
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More Than A Clock
The new atomic clock was developed by physicists at the National Institute of Standards and Technology (NIST). Their new atomic clock was based on the rare-Earth elementytterbium. They used a grid of laser beams known as an optical lattice to capture thousands of ytterbium atoms which naturally tick by switching between two energy levels — an action known as atomic electron transition, which takes a few nanoseconds. With each tick, or change in energy level, the electrons emit microwave energy which is detected. The physicists compared two of these ytterbium clocks and achieved the Holy Grail of physics.
The ytterbium clock’s record-breaking performance was measured in three ways:
- Systematic uncertainty: The natural vibrations of the ytterbium atoms. The ytterbium clock was off by only one billionth of a billionth.
- Stability: The frequency of the ytterbium clock changing in a specified time. The ytterbium clock changed by only 0.00000000000000000032 over a day.
- Reproducibility: The rate of two ytterbium clocks tick at the same frequency. In 10 comparisons, the difference was again less than one billionth of a billionth.
“Systematic uncertainty, stability, and reproducibility can be considered the ‘royal flush’ of performance for these clocks,” project leader Andrew Ludlow said in a press release. “The agreement of the two clocks at this unprecedented level, which we call reproducibility, is perhaps the single most important result, because it essentially requires and substantiates the other two results.”
A Challenge Against Classic Relativity
The theory of general relativity by Albert Einstein proved that time passes differently relative to gravity. Atomic clocks tick differently depending on gravity: the stronger the force, the slower the tick, and vice versa. What this means is that, the further you are away from the center of a massive object, the less gravity there is. For instance, time passes faster at the peak of Mountain Everest than the base of Mariana Trench. This effect is not really noticeable, perhaps only a millionth of a second, though measurable, but its real.
According to the physicists, now that they’ve invented a clock so accurate than the gravitational effect on time, it could measure Earth’s gravitational shape. Usually, Earth’s gravitational shape is measured via tidal effects often several centimeters accurate, but the new clock could measure the accuracy down to less than a centimeter. And as a matter of fact, the ytterbium clock could even measure space-time, detect gravitational waves, might be possible to even measure dark matter. With such level of accuracy and precision, this device is more than just a clock.
“The demonstrated reproducibility shows that the clocks’ total error drops below our general ability to account for gravity’s effect on time here on Earth,” as Ludlow explains. “Hence, as we envision clocks like these being used around the country or world, their relative performance would be, for the first time, limited by Earth’s gravitational effects.”
The Game Changing Ytterbium
The accuracy of the ytterbium clock could also be affected other environmental factors. It has to be kept cool and isolated from any stray electrical fields like heat effects so that they can be accounted and corrected for. Physicists are now building portable ytterbium clock that are being tested and compared in labs with other clock like the cesium and rubidium. This new development is seen as a game changer in atom clock evolution. They could also be moved to other locations to study relativistic geodesy techniques.
Previously, atomic clocks were based on the element cesium, and has been in use since the 1960s under the International System Units (ISU). Here’s the catch: with the development of the ytterbium clock, its game over for cesium. The first cesium clock was built in 1955, and has been the standard for measuring time. Technically, the definition of a second has been in use since 1967, and it states:
“The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.”
Decades later, it was clarified that cesium has to be at zero degree Kelvin (-273 degrees Celsius, or -460 degrees Fahrenheit) — that’s absolute zero. Other atomic clocks made from rubidium were also made portable, but not as accurate as the cesium. The rubidium was good enough for applications like Global Positioning System (GPS), cellphone towers, and transmitting television frequencies. But with the introduction of the new ytterbium atomic clock, we’re yet to witness the best of the two with unprecedented scientific accuracy and portability.
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Written by: Nana Kwadwo, Mon, Apr 29, 2019.