Every clock in your house probably tells a slightly different time. Now picture those clocks as the most precise instruments humanity has ever built, so accurate that they wouldn’t lose or gain a second for billions of years. That’s the challenge a team of international scientists recently tackled when they connected 10 of the world’s most advanced atomic clocks across six countries in the largest coordinated timekeeping experiment ever conducted.
The results, published in the journal Optica, reveal both incredible precision achievements and surprising discrepancies that could reshape how we define time itself. While some clocks agreed to within their expected precision limits, others showed unexpected differences that have major implications for the future of global timekeeping.
These optical clocks are being considered as replacements for the current international time standard, with scientists hoping to redefine the second — the fundamental unit of time — by 2030. But first, they need to prove these clocks can work together reliably on a global scale.
Why Ultra-Precise Timekeeping Matters
Accurate time underpins everything from GPS navigation to financial markets to internet communications. “The accurate time and frequency signals provided by atomic clocks are essential for many everyday technologies — like GPS, managing power grids and keeping financial transactions in sync,” said Helen Margolis, head of time and frequency at the National Physical Laboratory (NPL) in the United Kingdom, in a statement.
The current international time standard relies on cesium atomic clocks. Optical clocks are now about 100 times more accurate than the best cesium clocks and can measure time so accurately that they would lose or gain less than one second over billions of years.
Building incredibly precise clocks is one challenge; getting them to agree with each other across vast distances is entirely another. “Optical clocks provide ultraprecise frequency references that are vital for international metrology as well as for tests of fundamental physics,” the researchers wrote in their paper.
The Global Experiment: 45 Days of Synchronized Science
For 45 days starting February 20, 2022, research teams in Finland, France, Germany, Italy, the United Kingdom, and Japan ran their optical clocks simultaneously while connected through fiber optic cables and satellite links as part of a European collaborative project called ROCIT.
Each clock traps and cools individual atoms to near absolute zero, then uses laser light to measure their natural vibrations with extraordinary precision. The clocks use different types of atoms: some use strontium, others use ytterbium, and one uses indium ions. Each atomic species vibrates at its own unique frequency, like different musical notes. By comparing these frequencies, scientists can test whether the fundamental constants of physics remain truly constant across time and space.
European teams relied on a network of fiber optic cables stretching thousands of kilometers, including a 1,023-kilometer link between France and Italy. For distant locations like Japan, scientists used satellite-based GPS technology through a technique called Integer Precise Point Positioning (IPPP). However, satellite linking has limited precision due to measurement uncertainties caused by factors like signal noise or instrument limits.
Mixed Results Reveal Both Promise and Problems For Atomic Clocks
The experiment produced 38 different frequency ratio measurements between pairs of clocks. Four of these comparisons were conducted directly for the first time, and many others were measured with much greater accuracy than before. Many clocks agreed to within their expected precision limits, sometimes to extraordinarily high precision.
However, several concerning discrepancies emerged. Most notably, there appeared to be systematic problems with the Italian team’s equipment during the measurement period.
“Not all the results confirmed what we expected, and we observed some inconsistencies in the measurements,” said Rachel Godun, principal scientist at NPL. “However, comparing so many clocks at once and using more than one technique for linking the clocks made it easier to identify the source of the problem.”
These findings demonstrate a key point about precision timekeeping: “This serves to illustrate the importance of carrying out large, coordinated measurement campaigns with multiple clocks and links running simultaneously in order to identify and eliminate such inconsistencies,” the authors write in their paper.
Beyond timekeeping applications, this experiment marks several scientific firsts. These measurements help scientists search for signs that the fundamental constants of nature might be changing over time, a possibility that could revolutionize our understanding of physics. Marco Pizzocaro, a senior researcher at the Instituto Nazionale Di Ricerca Metrologica (INRiM) in Italy, believes their work “could also be used for carrying out tests of fundamental physics, such as searching for dark matter or testing the basic rules of physics.”
The Path Forward for Global Timekeeping
The research builds a key step toward the international physics community’s goal of redefining the International System of Units second to use optical clocks instead of the current cesium-based standards. The transition, targeted for 2030, requires demonstrating that different optical clocks worldwide can maintain consistent, reliable operation.
“Comparing multiple clocks at the same time and using more than one type of link technology provides far more information than the mostly pairwise clock comparisons that have been carried out to date,” said Thomas Lindvall, senior scientist at VTT MIKES in Finland. “With a coordinated set of measurements, it becomes possible to check consistency while also providing more trusted results. These results can help determine which optical clock(s) should be used in the new definition of the second.”
However, major challenges remain. “These measurements provide critical information about what work is still needed for optical clocks to achieve the precision and reliability required for use in international timekeeping,”
The experiment identified areas where more work is needed. To confirm that all clocks are performing as expected, measurement uncertainties must be reduced to match the precision of the clocks themselves. Repeated measurements will then be needed to confirm reliable operation necessary to build confidence in both the clocks and the links.
Scientists plan more extensive comparison campaigns as optical clock technology continues improving. Future experiments will likely include more clocks, longer measurement periods, and better fiber optic connections to reduce uncertainties further.
“Our findings could help to improve the performance of next-generation optical clocks, unleashing entirely new applications and advancing scientific endeavors that rely on time and frequency,” said Margolis.
While this experiment demonstrated that a global network of optical clocks is feasible, it also showed that achieving perfect synchronization across continents remains a formidable technical challenge. In an age where milliseconds can mean millions of dollars in financial markets and nanoseconds matter for GPS accuracy, this research brings us closer to a future where humanity’s most fundamental measurement — time itself — will be based on the quantum mechanical behavior of individual atoms, synchronized across the globe with previously unimaginable precision.
Source : https://studyfinds.org/atomic-clocks-connected-across-6-countries/