UNLV alumna Elizabeth Donley has many second thoughts.
As chief of the , she is helping redefine a basic unit of time — the second.
“This will take many years of work by timekeeping labs around the world,” says Donley, ’94 BS and ’96 MS Physics. She went on from UNLV to earn her Ph.D. at Europe’s equivalent of MIT, the Swiss Federal Institute of Technology in Zürich. “It’s fun and exciting, and we want to get it right because it requires international cooperation. We’ve teamed up to do some of the world’s most advanced atomic physics experiments.”
Scientists realized decades ago that the second could no longer be defined by astronomical means. That’s because the Earth’s rotation is slowing. As a result, three hours have been lost over the past 2,000 years. The second remains one-86,400th of a day, but high-tech companies and scientists need a definition untethered to our erratic planet. Interestingly, this problem exists beyond Earth. Time runs faster on the Moon; a clock there would pick up 56 microseconds, or millionths of a second, every day.
The solution came with the post-WWII invention of fantastically precise atomic clocks. They measure time based on something that remains constant—the frequency of microwave radiation absorbed by the ground state of a cesium atom, a frequency that turns out to be 9,192,631,770 per second. So, in 1967 that’s how the scientific community agreed to define a second.
Now there are newer, better optical atomic clocks. These more advanced timepieces can already measure frequencies 100 times more accurately than in the past — now at 10 to the 16th level of accuracy achieved with the cesium definition. So, the definition of a second must be rejiggered.
Not surprisingly, Donley and the international team at the General Conference on Weights and Measures are taking their time to decide on the best course of action. Among other matters to be resolved is whether another atom will replace cesium. “There’s no consensus yet on which approach to take, and we need to do a lot of work to meet mandatory criteria,” she says. The conference, which meets every four years, will convene in 2026. A final decision is expected in 2030.
New technologies, such as quantum networking, are driving the improved second. “These will be linked by lasers instead of by signals on copper cables or radio waves,” says Donley. “They’ll need optical synchronization. But everybody who makes measurements of precision frequencies at that high level will benefit from the redefinition, because if you have an optical frequency standard, you can have results 100 times faster.”
As division chief, Donley squeezes in time to conduct research while riding herd over administrative duties such as overseeing recruiting and processing grants. But the most important part of her job, according to her, is working with users of global positioning satellite data to keep them safe from hacking, jamming, and other service disruptions.
“One of the things I’m doing a lot now is educating users of precision time about system vulnerabilities that could cause outages,” she says.
Ultra-precise timekeeping is essential for GPS. “The global positioning satellite system currently operates on timing uncertainties on an order of nanoseconds. That's because it takes light about a nano second to travel one foot. It’s the limit at which you can know your position,” she says.
A Natural Leader in the Lab
Much of the critical infrastructure in the U.S. developed based on the ability to receive GPS signals, and NIST can provide users with precision time signals that can be independent from GPS. “We’re trying to make that more available to companies and institutions like the Department of Energy,” says Donley. She coordinates with potential customers who want NIST to deliver signals to them over optical fiber or satellites.
Her work includes increasing the representation of women in her department at NIST’s Boulder, Colorado, office which has about 1,000 employees.
Being a woman in a male-dominated field has not hindered her career, though there are moments when she notices how some perceive her. “If I visit another institute or meet someone who doesn’t know me, they probably don’t know how much I understand about what they’re doing,” she surmises.
“I think it’s getting better. Last year we set a goal of increasing the number of permanent female staff in my division from 15 to 20 percent. We succeeded, but, still, it’s only 20 percent.”
A native of Pueblo, Colorado, she moved with her family to Las Vegas when she was 16. The decision to attend UNLV was easy. One of her high school classes toured the physics department and longtime professor Lon Spight chatted with them about quarks and theoretical physics. “He was enchanting,” Donley recalls.
She worked for three years in the lab of professor David Shelton. They co-authored papers on non-linear optics and second harmonic generation for measuring atomic and molecular hyperpolarizabilities. “An amazing mentor,” she says. Today, 25 years later, his students still use an experiment involving a muon telescope that she built for his lab.
“Elizabeth ranks up there as one of my best students ever,” recalls Shelton. “She was a natural in the lab. I remember the good students, and she was wonderful.”
She collaborated with Nobel Prize-winning physicist Carl Wieman as a post-doc researcher at the University of Colorado, where her leadership skills emerged alongside her research talent. “She did great work and was a really valuable member of my group not just in the science but in keeping everyone working effectively,” he says.
But on one occasion Donley did give her prestigious mentor reason to worry. She corralled other lab members to join her on a rock climbing trip. “I was rather ambivalent about it, but she brought them all back safely,” he says.
Wasting No Time
A lifelong climber, Donley has tackled long alpine routes in Wyoming’s Wind River Mountains and the Rocky Mountain National Park. Her peak achievement came 10 years ago. At age 42, she took the Chiaro di Luna route up St. Exupery, a spear-shaped 2,500-foot massif that juts skyward in Argentina’s Patagonia region.
To accomplish the feat, Donley, her husband Cory, and another climber spent 33 hours on the wall. Getting to the remote site was hard. Carrying their own gear, they hiked 12 miles, six of which were over a crevassed glacier. “It was a pretty serious endeavor,” she says.
Climbing emphasizes the power of mind over matter, according to Donley. She also mountain bikes and cross-country skis near her Leadville, Colorado, home. “I’m not the strongest person in the world physically, but I make up for it by doing pretty well at the mental aspects of the sport.”
Despite her career's esoteric nature, it has given her no special insights into the meaning of time. “Some people are attracted to those philosophical questions, but I try to steer clear of them,” she says.
The demands of her job have, however, made her an efficient user of time. She comes to meetings right on time or one minute late, and she is not a procrastinator. “If I was,” she says, “I probably wouldn’t be very good at what I do.”
