Cosmic rays can help synchronize world clocks

The world has a robust and accurate timing system that regulates our clocks. Humanity uses it for everything we do, from our financial systems to satellite navigation, computer and telephone networks and GPS. But the current system is not perfect and has vulnerabilities to cyberattacks and disruptions. Given how important accurate timekeeping is to our society (as a fundamental foundation of 21st century life), experts are always looking for ways to improve the system and add redundancy. Researchers at the University of Tokyo have taken a big step in this direction, developing a new method of time synchronization that takes advantage of cosmic rays to calibrate the world’s clocks.

There are two big challenges in timing. The first is to maintain an accurate clock over a long period of time. Humans have gradually improved in this area over the centuries, from ancient water clocks to mechanical pendulum clocks of the 19th century. Modern watches operate largely using the rhythmic vibrations of quartz crystals, although even these do not match the precision of atomic clocks, which keep time by taking advantage of the fact that the energy required to change the orbit of an electron around an atom is consistent throughout the universe. With these atomic measurements, the latest and greatest atomic clocks lose only about one second every ten million years.

But the second – and arguably the toughest timekeeping challenge – is making sure multiple clocks around the world are in tune with each other. Clocks aboard orbiting satellites, like the ones we use for GPS, must be regularly calibrated from ground-based atomic clocks to operate consistently (and they must account for time dilation, because time moves differently in orbit than here in Earth’s gravity well. Thanks Einstein!) It’s this timing problem that Professor Hiroyuki Tanaka of the University of Tokyo hopes to improve with a new method.

Tanaka calls the method CTS, which stands for Cosmic Time System, and it relies on sensors that detect particles left behind by the collision of cosmic rays with the Earth’s atmosphere. The cosmic rays are scattered at an altitude of about fifteen kilometres, causing a shower of particles, some of which reach the ground, including muons moving at a speed close to light. CTS devices in multiple locations can detect these muons and use them to synchronize with each other. Each muon shower has its own unique signature, allowing CTS devices to identify a singular event and synchronize with each other based on that event.

Muons penetrate through rock and water, meaning these devices would work inside buildings, in submarines and in underground railway tunnels. “Satellite time synchronization has so many blind spots at the poles, in mountainous regions, or underwater,” Tanaka said, “and CTS could fill those gaps and more.”

And because they’re natural signals, they can’t be interfered with or hijacked like artificial GPS signals.

Tanaka thinks CTS could revolutionize the way timing works, and perhaps navigation too. “It’s relatively easy to keep time accurately these days. For example, atomic clocks have been doing this for decades now,” Tanaka said. “However, these are large and expensive devices that are very easy to disrupt. This is one of the reasons I worked on a better way to keep time. The other is that, related to time measurement, position measurement could also be improved. So really, CTS is a precursor to a potential GPS replacement, but it’s still a bit further down the line.

Learn more:

“Keeping Time with the Cosmos: A New Method for Synchronizing Devices on Earth Uses Cosmic Rays” University of Tokyo.