Physicists are on the brink of redefining time

Time is a construct — and it’s made of atoms.


AROUND THE WORLD, we are all controlled by the same, invisible force that tells us when to wake up, when to work, and even when to socialize: time.

After this past year, the concept of time may seem less real than ever, but according to a team of physicists in Colorado, that couldn’t be further from the truth. The team used three different elements to measure the length of a second.

To date, atomic clocks (which absorb and emit photons at regular frequencies to keep time) are the most accurate way to measure the passage of time in seconds, but their accuracy has been stagnated for more than a decade.

Using both optical fibres and invisible laser transmission of data, the research team measured the meaning of a second more accurately than ever before. They did it by looking at minute (the measure of size, not time) differences between time kept by the atoms — a crucial step toward redefining time itself.


WHAT’S NEW — Previous attempts to measure these minute differences between how atoms keep time — also referred to the ratio between them — had only ever delivered an accuracy of up to 17 digits.

But now using their new model, which includes the first-ever use of a ‘free-space link’ for this purpose (essentially, laser pulses of data going through the air instead of a cable,) the University of Colorado’s BACON team (Boulder Atomic Clock Optical Network) has now measured this ratio reliably out to 18 digits.

The research was published Wednesday in the journal Nature.

atomic clock
Cesium has long reigned supreme as the element of choice in atomic clocks, but that could soon be changing.Nature

WHY IT MATTERS — One digit might not make or break a grade on your final exam or even your credit score, but for extremely tiny measurements in physics, this is a big deal.

Rachel Godun is a senior research scientist in the Time and Frequency group at the National Physical Laboratory in the U.K. She wrote an unaffiliated essay on this work also published this week in Nature. She says that the kind of precision demonstrated in this study is literally astronomical.

“Such frequency-ratio measurements are no mean feat, and are equivalent to determining the distance from Earth to the Moon to within a few nanometres,” says Godun in the essay.

The research team reports continued refinement of atomic clock measurements using this model has the potential to redefine the second as we know it and can help physicists test fundamental theories of the universe — including relativity and dark matter — by measuring atomic perturbations even more precisely.


HERE’S THE BACKGROUND — The first atomic clock began ticking in 1949. It was powered by anammonia molecule, but a cesium isotope quickly became the standard only a few years after.

Since then, scientists have relied on these incredibly precise clocks, which are largely immune to earthly headaches like earthquakes, to help keep precise time. This measurement is used to not only define time itself, but to guide satellites in orbit via GPS as well.

Such a clock, called the “Master Clock,” resides at the U.S. Naval Observatory (USNO) in D.C. In addition to its role as a historic scientific institution, the USNO is also the residence for the vice president of the United States — meaning it’s where Vice President Kamala Harris will live once renovations are complete.

WASHINGTON, DC - MARCH 23: The residence of the Vice President is seen as Karen Pence, who is the wife of Vice President Mike Pence hosts a gathering of women service members in recognition of Women's History Month on the grounds of the United States Naval Observatory on Thursday March 23, 2017 in Washington, DC. (Photo by Matt McClain/The Washington Post via Getty Images)
In addition to being home to the U.S. Vice President, the U.S. Naval Observatory is also home to one of the nation’s essential atomic clocks.The Washington Post/The Washington Post/Getty Images

Historically, atomic clocks have worked used cesium to measure fractions of time by counting the jumps the atoms make between different energy states when exposed to certain radio-wave frequencies. Since 1967, the official definition of a second has been “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 cesium-133 atom.”

In other words, there are just over 9 billion cesium energy jumps in one second.

While this method has worked for decades, it is still far from perfect. The oscillation frequency of cesium clocks is in the microwave region of the electromagnetic spectrum (the rainbow that stretches from low energy radio waves to high energy gamma rays and describes all possible frequencies of incoming light.) Newer designs for atomic clocks instead focus on elements whose frequencies would in the optical spectrum (the part we can see) instead. These frequencies would be 100,000 times faster than the microwave range ones emitted from cesium clocks and in turn 100 times more accurate…


F. Kaskais Web Guru

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