This may look like a mad scientist's garage sale, but it's actually the most precise clock ever built.
What a makes a good clock? Andrew Ludlow, a physicist at the , says one of the most important criteria is stability.
you could imagine a grandfather clock and see the pendulum swinging
back and forth, ideally that pendulum would swing back and forth very
uniformly," Ludlow says. "Each swing would take exactly the same amount
That's stability. But what if something perturbs the system, like a mischievous toddler?
that toddler shaking the grandfather clock itself — that oscillation
period could vary quite a bit," Ludlow says. "How much that ticking rate
varies determines the precision with which you can measure the
evolution of time."
Ludlow is a clockmaker, but his clocks
don't have pendulums or gears. They are atomic clocks that rely on what
Ludlow calls "the natural internal ticking of the atom."
atom of a given element has its own characteristic resonant frequency.
The speed of that vibration is very consistent and very fast — there are
quadrillions of "ticks" every second. Atomic-clock makers use the
regularity of these vibrations to keep time with extreme accuracy.
can't mess up these clocks, but there's still a little instability.
Atoms move around, and that makes their vibrations slightly harder to
measure. So Ludlow and his team used a lattice of lasers to trap the
atoms and then cool them down. With the atoms frozen in place, the
scientists could more accurately measure their vibration.
Ludlow's clock is 10 times more accurate than the last model. It's the most precise atomic clock ever built.
getting to a meeting on time doesn't require this type of precision,"
Ludlow says. "But believe it or not, there's a number of both scientific
and technical applications."
Better atomic clocks will facilitate and faster telecommunication networks. And some physicists are excited about another application: testing Einstein's .
"Today many scientists believe that the theory of relativity is incompatible with other physical theories," Ludlow says.
predicted that certain physical properties, like the strength of the
interaction between photons and electrons, or the ratio of the mass of
electrons and protons, should never change. But competing theories say
that those "fundamental constants" might actually fluctuate and such
changes would slightly influence the ticking speed of atomic clocks.
"As clocks become better and better, they become more and more useful tools to explore this possible variation," Ludlow says.
also predicted that clocks in different gravitational fields would tick
at different speeds. For example, a clock in Boulder, Colo., which is a
mile above sea level, would feel a slightly weaker gravitational pull
than a clock at sea level in Washington, D.C. As a result, it would tick
just a bit faster — and after 200,000 years it would be a full second
That's not much of an effect, but it's big enough for
most atomic clocks to measure. And Ludlow's clock can register the
change in gravity across a single inch of elevation. That kind of
sensitivity will allow scientists to test Einstein's theories with
greater precision in the real world.