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BOULDER, Colorado -- The best timepiece in the world lives deep in a '60s-style concrete government building, where it resembles nothing so much as a teenager's science-fair project: a jumble of polished lenses and mirrors converging on a gleaming silver cylinder, all protected by a tent of clear plastic nailed to a frame of two-by-fours.
Called the NIST-F1, this atomic clock is more accurate for prolonged periods than any other clock -- an order of magnitude better than the one it replaced in 1999. When the F2 down the hall goes online next year, it will similarly dwarf the F1.
"We basically have a Moore's Law in clocks," says Tom O'Brian, chief of the Time and Frequency Division of the National Institute of Standards and Technology, or NIST. "They improve by a factor of 10 every decade."
But that precision has brought the science of time to an existential crisis. Since 1904, when NIST purchased a pendulum clock from a German clockmaker, the institute has been America's official timekeeper, caring for the most accurate time-interval standards in the world. It still serves that role. But the latest generation of atomic clocks here, and at time labs around the world, has reached a level of precision well beyond such parochial applications, and much of the clocks' accuracy is wasted.
As a result, the institute is changing. No longer merely concerned with making sure America knows what time it is, the 400 scientists, engineers and staff at NIST's Time and Frequency Division are increasingly interested in what they can do with a clock. They're working to shrink atomic clocks to the size of a grain of rice, and testing new breeds of clocks precise enough to detect relativistic fluctuations in gravity and magnetic fields. Within a decade their work could have a significant impact on areas as diverse as medical imaging and geological survey.
"There's a lot of room here to (do more than) just make better and better clocks," says O'Brian.
With its fading beige walls and checkered linoleum floors, NIST's Time and Frequency Division hardly invites a sense of precision. Distracted-looking scientists in slightly rumpled button-downs roam the halls, occasionally sparing a quizzical look for outsiders. Graduate students wander in funny T-shirts, passing offices and labs crammed with manila folders and well-used tools, while cables and pipes zigzag across the ceiling.
But NIST's clocks have long been indispensable to the United States. Invisible to most of us, precision time is the heartbeat of today's digital world. Atomic clocks installed in every cellphone site manage the handoff from one tower to the next. Space-based clocks tell your car's dashboard GPS where you are. Lesser clocks keep your radio tuned, and when stability-control technology on your car kicks in, they keep you on the road and out of accidents. Those clocks are all set -- through several layers of indirection -- by the cesium clocks ticking in NIST's inner sanctum.
That's the present. Leo Hollberg, supervisory physicist of the Optical Frequency Measurements Group, is more concerned with the future of time. He leads the way through darkened labs glowing with laser lights that wander paths of mirrors and lenses from room to room.
These rooms are where NIST is testing a new way of tapping the precision time built into elements like calcium and ytterbium. Cesium clocks like NIST-F1 use lasers to slow a cloud of cesium atoms to a measurable state, then tune a microwave signal as close as possible to the cesium's resonant frequency of 9,192,631,770 cycles per second (See sidebar: How the World's Best Clock Works). In this manner, the F1 achieves a precision topping 10-15 parts per second.
At least, in theory. To tap the F1's full accuracy, scientists have to know their precise relative position to the clock, and account for weather, altitude and other externalities. An optical cable that links the F1 to a lab at the University of Colorado, for example, can vary in length as much as 10 mm on a hot day -- something that researchers need to continually track and take into account. At F1's level of precision, even general relativity introduces problems; when technicians recently moved F1 from the third floor to the second, they had to re-tune the system to compensate for the 11-and-a-half foot drop in altitude.
Cesium, though, is a grandfather clock compared to the 456 trillion cycles per second of calcium, or the 518 trillion provided by an atom of ytterbium. Hollberg's group is dedicated to tuning into these particles, which hold the key to a scary level of precision. Microwaves are too slow for this job -- imagine trying to merge onto the Autobahn in a Model T -- so Hollberg's clocks use colored lasers instead.
"Each atom has its own spectral signature," says Hollberg. Calcium resonates to red, ytterbium to purple. At their most ambitious, NIST scientists hope to wring 10-18 out of a single trapped mercury ion with a chartreuse light -- slicing a second of time into a quadrillion pieces.
At that level, clocks will be precise enough that they'll have to correct for the relativistic effects of the shape of the earth, which changes every day in reaction to environmental factors. (Some of the research clocks already need to account for changes in the NIST building's size on a hot day.) That's where the work at the Time and Frequency Division begins to overlap with cosmology, astrophysics and space-time.
BOULDER, Colorado -- The best timepiece in the world lives deep in a '60s-style concrete government building, where it resembles nothing so much as a teenager's science-fair project: a jumble of polished lenses and mirrors converging on a gleaming silver cylinder, all protected by a tent of clear plastic nailed to a frame of two-by-fours.
Called the NIST-F1, this atomic clock is more accurate for prolonged periods than any other clock -- an order of magnitude better than the one it replaced in 1999. When the F2 down the hall goes online next year, it will similarly dwarf the F1.
"We basically have a Moore's Law in clocks," says Tom O'Brian, chief of the Time and Frequency Division of the National Institute of Standards and Technology, or NIST. "They improve by a factor of 10 every decade."
But that precision has brought the science of time to an existential crisis. Since 1904, when NIST purchased a pendulum clock from a German clockmaker, the institute has been America's official timekeeper, caring for the most accurate time-interval standards in the world. It still serves that role. But the latest generation of atomic clocks here, and at time labs around the world, has reached a level of precision well beyond such parochial applications, and much of the clocks' accuracy is wasted.
As a result, the institute is changing. No longer merely concerned with making sure America knows what time it is, the 400 scientists, engineers and staff at NIST's Time and Frequency Division are increasingly interested in what they can do with a clock. They're working to shrink atomic clocks to the size of a grain of rice, and testing new breeds of clocks precise enough to detect relativistic fluctuations in gravity and magnetic fields. Within a decade their work could have a significant impact on areas as diverse as medical imaging and geological survey.
"There's a lot of room here to (do more than) just make better and better clocks," says O'Brian.
With its fading beige walls and checkered linoleum floors, NIST's Time and Frequency Division hardly invites a sense of precision. Distracted-looking scientists in slightly rumpled button-downs roam the halls, occasionally sparing a quizzical look for outsiders. Graduate students wander in funny T-shirts, passing offices and labs crammed with manila folders and well-used tools, while cables and pipes zigzag across the ceiling.
But NIST's clocks have long been indispensable to the United States. Invisible to most of us, precision time is the heartbeat of today's digital world. Atomic clocks installed in every cellphone site manage the handoff from one tower to the next. Space-based clocks tell your car's dashboard GPS where you are. Lesser clocks keep your radio tuned, and when stability-control technology on your car kicks in, they keep you on the road and out of accidents. Those clocks are all set -- through several layers of indirection -- by the cesium clocks ticking in NIST's inner sanctum.
That's the present. Leo Hollberg, supervisory physicist of the Optical Frequency Measurements Group, is more concerned with the future of time. He leads the way through darkened labs glowing with laser lights that wander paths of mirrors and lenses from room to room.
These rooms are where NIST is testing a new way of tapping the precision time built into elements like calcium and ytterbium. Cesium clocks like NIST-F1 use lasers to slow a cloud of cesium atoms to a measurable state, then tune a microwave signal as close as possible to the cesium's resonant frequency of 9,192,631,770 cycles per second (See sidebar: How the World's Best Clock Works). In this manner, the F1 achieves a precision topping 10-15 parts per second.
At least, in theory. To tap the F1's full accuracy, scientists have to know their precise relative position to the clock, and account for weather, altitude and other externalities. An optical cable that links the F1 to a lab at the University of Colorado, for example, can vary in length as much as 10 mm on a hot day -- something that researchers need to continually track and take into account. At F1's level of precision, even general relativity introduces problems; when technicians recently moved F1 from the third floor to the second, they had to re-tune the system to compensate for the 11-and-a-half foot drop in altitude.
Cesium, though, is a grandfather clock compared to the 456 trillion cycles per second of calcium, or the 518 trillion provided by an atom of ytterbium. Hollberg's group is dedicated to tuning into these particles, which hold the key to a scary level of precision. Microwaves are too slow for this job -- imagine trying to merge onto the Autobahn in a Model T -- so Hollberg's clocks use colored lasers instead.
"Each atom has its own spectral signature," says Hollberg. Calcium resonates to red, ytterbium to purple. At their most ambitious, NIST scientists hope to wring 10-18 out of a single trapped mercury ion with a chartreuse light -- slicing a second of time into a quadrillion pieces.
At that level, clocks will be precise enough that they'll have to correct for the relativistic effects of the shape of the earth, which changes every day in reaction to environmental factors. (Some of the research clocks already need to account for changes in the NIST building's size on a hot day.) That's where the work at the Time and Frequency Division begins to overlap with cosmology, astrophysics and space-time.
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