NEW ATOMIC CLOCK
The clock keeps time more precisely than any before it. Page WA-5
Scientists have invented a clock that keeps time more precisely than any that have come before.
The clock is so accurate that it won’t gain or lose more than one second in 14 billion years — roughly the age of the cosmos. Its ticking rate is so stable that it varies by only 0.000000000000000032 percent over the course of a single day.
That level of exactitude is not really necessary for those of us who rely on clocks to get us to a doctor’s appointment on time, or to know when to meet up with friends.
But keeping time is just the beginning. This new clock is so exact that it could be used to detect dark matter, measure the gravitational waves that ripple across the universe, and determine the exact shape of Earth’s gravitational field with unprecedented precision.
Indeed, these hyper-accurate clocks can help scientists better probe the mysteries of the cosmos, experts said.
“It turns out that if you have all these digits of precision for making a measurement, it can give you a microscope onto our very universe,” said physicist Andrew Ludlow of the National Institute of Standards and Technology in Boulder, Colo. Mr. Ludlow led the work that produced the new clock, which was described this week in the journal Nature. Since the 1960s, time has been measured by so-called atomic clocks that use the natural oscillations of a cesium atom as a pendulum. Think of it as a watch with a hand that ticks just over 9 billion times per second.
The optical lattice clock Mr. Ludlow and his colleagues developed measures the much faster oscillations of a ytterbium atom. Its atomic pendulum swings about 10,000 times faster, at a speed of 500 trillion times per second.
“Cesium is a beautiful atomic system, but we have reached the basic limits of how good it can be,” Mr. Ludlow said.
Optical lattice clocks have been around for only 15 years, and they are still in the development stage, Mr. Ludlow said. Scientists continue to tinker with them, gradually increasing their accuracy with each new adjustment.
Most of the improvements in the latest iteration are due to a new heat shield that Mr. Ludlow’s group developed. It protects the ytterbium atoms from the effects of heat and electric fields, which can interfere with their natural oscillations.
“We want to be sure that when we are measuring the ticking rate of the atom, we are measuring the rate Mother Nature gave it, and that it is not perturbed or shifted due to an environmental effect,” he said.
With so many oscillations, the ytterbium clock can detect shifts in the gravitational field of our planet with unprecedented precision, Mr. Ludlow and his coauthors wrote in Nature.
As Einstein’s theory of general relativity predicts, time moves differently depending on where you are in a gravity field.
A clock on top of a mountain — far from Earth’s center — will tick a tiny bit faster than a clock at the base of that same mountain.
It’s not a mechanical error. Time actually passes faster at the top of that mountain.
Most clocks aren’t accurate enough to register that extremely subtle difference. After all, in 10 years, two clocks that are 1,000 meters apart in altitude will be off by just 31-millionths of a second.