Curvature of space-time measured using 'atomic fountain'

 

In 1797, English physicist Henry Cavendish measured the strength of gravity with a device made of lead spheres, wooden rods and wire. In the 21st century, researchers are doing something very similar with slightly more sophisticated tools: atoms.

 

Gravity might be an early subject in preliminary physics classes, but that doesn't mean researchers aren't still trying to measure it with ever-increasing accuracy. Now, a team of physicists has done it using the effects of time dilation — the slowing of time caused by increased velocity or gravitational force — on atoms. In a report published online today (Jan. 13) in the journal Science, the scientists’ state that they've been able to measure the curvature of space-time.

 

The experiment is part of an area of science known as atom interferometry. It takes advantage of a principle of quantum mechanics: just as a light wave can be characterized as a particle, a particle (such as an atom) can be represented as a "wave packet." And just as light waves can overlap and generate interference, so too can matter wave packets.

 

In particular, if an atom's wave packet is split in two, permitted to do something, and then recombined, the waves might not line up any longer — in other words, their phases have changed.

 

"One tries to extract valuable information from this phase shift," Albert Roura, a scientist at the Institute of Quantum Technologies in Ulm, Germany, who was not involved in the new research, told Space.com. Roura wrote a "Perspectives" piece about the new study, which was published online in the same topic of Science today.

 

Gravitational wave sensors work via a similar principle. By studying particles in this way, researchers can adjust the numbers behind some of the key workings of the universe, such as how electrons act and how strong gravity really is — and how it subtly changes over even quite small distances.

 

It's that last effect that Chris Overstreet of Stanford University and his colleagues measured in the new research. To do this, they created an "atomic fountain," comprising of a vacuum tube 33 feet (10 meters) tall ornamented with a ring around the very top.

 

The scientists controlled the atomic fountain by shooting laser pulses through it. With one pulse, they propelled two atoms up from the bottom. The two atoms reached different heights before a second pulse shot them back down. A third pulse gathered the atoms at the bottom, recombining the atoms' wave packets.

 

The scientists found that the two wave packets were out of phase — a sign that the gravitational field in the atomic fountain wasn't completely constant.

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References:

Space.com, News Corner