| Scientists have created an optical lattice atomic clock so sensitive that its timekeeping is affected by gravitational changes due to height differences of as little as 2 centimeters. (Ye group and Steve Burrows / JILA) |
Excerpt from latimes.com
Scientists have created an atomic clock that is so precise that
it can detect tiny changes in the speed of its ticks depending on
whether it is 2 centimeters closer or farther from the center of Earth.
“Time
can be intricately connected to gravity,” said Jun Ye, a physicist
at JILA, a joint institute of the National Institute of Standards and
Technology and the University of Colorado, Boulder. “It sounds like
science fiction, but these measurements are a reality.”
The
ability of a hyper-sensitive clock to determine small differences in
altitude is based on Einstein’s prediction that the farther one gets
from the center of an attractor (like Earth), the faster time moves.
Researchers
have long ago proved this theory by comparing the speed of clocks
separated by vast differences, either on board satellites in orbits
a few dozen miles apart, or by comparing the ticks of clocks telling
time at sea level and those placed on a mountain top.
Five years
ago researchers at NIST created a clock so sensitive that it could
detect the difference in time between two elevations just a foot from
each other.
But the new clock is even better.
“Now
when we measure this very weird property of time fabric in the
laboratory, even a 2-centimeter change will result in a detectable time
change in the clock,” Ye said.
The clock is described Tuesday in Nature Communications. It is a tweaked version of an optical lattice clock that measures the oscillations of strontium atoms that have been trapped in a network of lasers.
Ye,
who is the principal investigator on the paper, explains that the clock
measures the speed of an electron as it zips around the nucleus of
a strontium atom at the rate of about a million billion orbits per
second.
To calculate this movement, the researchers hit a few
thousand strontium atoms at a time with what they call a “clock laser.”
The laser can be tuned so that the peaks and troughs in its electric
field match the oscillation of the electrons of the strontium atoms.
The
result is a clock that is several orders of magnitude more accurate
than the cesium microwave clock that governs official time today.
“The
clock we use now is like a watch with a hand that moves 9 billion times
per second,” Ye said. “The ‘watch’ we are working on moves at the speed
of a million billion times per second; we are basically keeping track
of ripples of light.”
In
this latest iteration of the optical lattice clock, researchers reduced
time-telling errors by installing highly sensitive thermometers around
the trapped atoms so the effects of heat from the surrounding
environment could be better measured. They were also able to reduce the
effects of the laser net on the individual atoms, and they used one of
the most stable lasers in the world to take the measure of the electron
movement.
These tweaks lead to a clock that is at least three
times more precise than the previous world-record holder introduced last
year, as well as increased stability of 50%. The authors are
anticipating continued progress.
A clock with this extreme level
of precision may seem like overkill, but it could be used to improve our
understanding of the shape of Earth, help to conduct tests of the
fundamental laws that govern space and time, and provide a new pathway
for investigating dark matter.
And the possibilities grow as the clocks grow more precise.
“If
we can make a clock 1,000 times more accurate, we could hear the
symphony of the universe,” Ye said. “For instance, you would sense how
space time shifts when a distant galaxy explodes.”
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Hyper-precise atomic clock detects tiny changes in the fabric of time
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