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Atomic watches are so accurate that they can measure gravity

An older version of an extremely stable ytterbium lattice watch at NIST. Ytterbium atoms are formed in an oven (large…

An older version of an extremely stable ytterbium lattice watch at NIST. Ytterbium atoms are formed in an oven (large metal cylinder to the left) and sent to a vacuum chamber in the center of the photo to be manipulated and probed by lasers. Laser light is transported to the clock by five fibers (like the yellow fiber in the lower center of the foot). (Credit: Burrus / NIST)

Time, like money, only seems important when it expires. But to physicists, time is always a big deal. Relativity tells us that the time flow depends on the circumstances you measure: Bells cross faster on mountain than at ground level, and the faster you go the slower the clock goes. Time depends on space.

However, thanks to the technological advances in atomic clocks – the most precise time-limiting devices we have thought – we can turn things around and determine physical parameters more carefully by studying the passage of time. Our understanding of space depends on the time.

The new watches, described today in the magazine Nature will also promise what better watches usually promise: improved time driving, communication and navigation technology. But besides their insights into the physical space around them, the units can also help find gravity waves, test predictions of relativity and hunting for dark matter. All this, only from super-corrected watches.

Atomic Clocking In

This may all seem quite complicated (and it is), so let’s start with the basics. As the author of the paper helps, “Time is tracked by counting oscillations of a frequency reference, such as the earth’s turns or pendulum turns. By referring to atomic transitions, the frequency (and thus time) can be measured more accurately than any other physical quantity. “Then count how often specific atoms alternate between energy levels and you get the most accurate ticks and tips.

The main name in atomic clock is the National Institute of Standards and Technology (NIST), and that’s where the current research comes from. The latest watches are dependent on 1000 atoms of ytterbium, cooled to almost absolute zero, caught within 1-D grid (ie columns) of laser beams. Through all measurements of atomic clock performance – minimizing errors at atomic frequencies, it is certain that the fortifications are stable, and the results are reproducible. The NIST researchers produced only incredibly precise watches. Their error bars are in the order of 10 -18 or one billionth of a billion.

Things of Things

In fact, these atomic watches are so exact, they are actually sensitive to gravity influences. Normally, the relativistic feelings of gravity are adaptive to the short-term flow of time for us to notice – but no longer. As the authors say, “If these bells were compared over a long baseline or used to distort comparisons with other bells around the world, the measurement would be limited by gravity knowledge on Earth’s surface.” That’s how they are so accurate that the only thing that can change their ticks and tocks would be gravity itself. Bells higher up, farther from the earth’s mass, would cross faster than bells downwards, due to relativity.

This is an important issue for the science of geodesy, which measures the shape and gravity of the earth. Our current image of the plane’s exact surface depends on satellites and computer modeling, which gives a pretty good resolution, down to a few centimeters. But these bells would bring that resolution far down to just a centimeter. Armed with two of these watches, researchers could compare the sea level on two different continents, an exact height of a mountain or any other altitude-based (and thus gravity-based) measurement that they care about.

And because the atomic watches are so sensitive to gravity, they can act as a kind of detector for any related activity. Gravitational waves, as they pass through us and this planet, would appear in these lessons’ readings. Extremely subtle experimental tests of Einstein’s theories are now also possible. And most tantalizingly, technology can help detect small amounts of dark matter, the invisible things that only interact with gravity, and make up much of the material of the universe.

To be clear, there are still possibilities. The authors have just built these atomic watches and showed how accurate they are. But now that they know the technology works well, a new future of physical discoveries can only be over us. It’s time.

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