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IF YOU EVER find yourself needing to check the time, you could do a lot worse than ask . Based at the JILA research institute in Boulder, Colorado, Ye has been working for 20 years on honing the design of that paragon of timepieces, the atomic clock. He says versions like his could help us snare more gravitational waves, check the fundamental constants of nature and perhaps push general relativity past breaking point.

Joshua Howgego: How do you make an atomic clock?

Jun Ye: People have made atomic clocks for many decades. The traditional way is to shine microwaves onto atoms, such as caesium or rubidium, to make their electrons flip from one quantum state – known as spin – to another at regular intervals. This flipping is the tick of the clock. In the clocks I make, the principle is the same. But we use laser light and shine it on strontium atoms, so electrons undergo energy transitions between two stable orbitals – and that’s the tick.

How good is your clock?

There are three important performance metrics. First: how precise is your clock, or how well can you measure time? Second: how reproducible is it? This refers to whether you can get the same kind of measurement after a day, a week, a year. Third: how accurate is it? Is it a time that everyone can agree upon, after all systematic effects have been properly accounted for? This is quite different from precision. If we wanted to use these clocks as a standard for time, and we had one clock in Boulder and one in London, then they’d need to agree.

In terms of precision, our clock is a mind-boggling 100,000 times better than the best microwave-based atomic clock. It’s been a tremendous improvement over the past 20 years. The clock is highly reproducible too. What’s less clear, so far, is how well different clocks will agree.

I read your clock would only drop a second in the lifetime of the universe.

We’re dealing with time intervals so small they are hard to grasp. Back in 2015, we did some calculations and converted the precision of the clock to a more understandable value. It came out as being precise to within 1 second in 14 billion years, which is the lifetime of the universe. Since then, the precision of the clock has got better – so now it is 1 second in multiple universe lifetimes.

Why make clocks this precise?

There are many secrets in the universe, many mysteries out there. It seems we’re missing something fundamental about the way reality works. One way to try and get answers is to do experiments with particle colliders involving higher and higher energy. For that, you’d need about $40 billion and 30 years to construct yet another machine to smash particles, which isn’t guaranteed to see something new. Precision clocks are a totally different and more accessible tool that will also allow us to search for new fundamental physics. One key area, for example, is time dilation on very small scales. If we can study this, it might tell us something new about the connection between quantum physics and gravity.

You recently used your clocks to measure time dilation.

When people first started to test if time dilation [the idea that clocks can experience time ticking at different speeds] was real, they compared clocks separated by kilometres using satellites and airplanes. There was a by my colleague in 2010 using clocks 33 centimetres apart and seeing dilation. Recently, we measured time dilation over a few hundred microns [millionths of a metre] with our strontium clock.

I think we need to go down further, so we can see time dilation over a few microns. This is where things get interesting. We’d potentially be able to see how things like entanglement [an intrinsic link particles can share after interacting] are affected by different curvatures in Earth’s gravitational field.

Is there a limit to how accurate clocks will get?

The universe is always singing this symphony of gravitational waves borne out of collisions of black holes and such like. If your clock gets so precise that it can no longer be shielded from this omnipresent gravitational wave background, that will be the end of the road for the atomic clock. This is still many decades away, though.

We don’t have to see this as a limitation. Clocks can potentially function as a new kind of detector for gravitational waves, a different way of observing them. One day we could have a network of clocks orbiting Earth, serving as a planet-scale antenna for gravitational waves. This might be able to pinpoint waves with sufficient precision that it could allow us to hear the echoes of the big bang from the edge of the universe. If we could get to that level, it would be fascinating.