Extreme measures: Atom interferometry's precision could make it the Swiss Army knife of physics

Science News,  Feb 16, 2008  by Ewen Callaway

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Adding an extra digit or two to constants like G may sound like the scientific equivalent of dotting i's and crossing t's, but physicists like Chu think otherwise. "It's not chasing after the last digits" he says. "It's chasing after the first digit of something radically new." Better telescope measurements of celestial orbits buttressed Newton's theory of gravity, and Einstein's theory of special relativity explained the results of Michelson and Morley's light experiments. Likewise, atom interferometry could augur the next scientific revolution, Chu says. "Whenever you make something orders of magnitude better and extend your ability to see, you're going to stumble onto something new."

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COLLIDING FRONTIERS A basement physics laboratory at Stanford might produce such a discovery. Kasevich's team is nearly finished building the world's biggest atom interferometer, a 10 m deep well. Several factors determine an interferometer's precision, but the distance the atoms can travel is a big part of it. The first experiments planned for the device include testing whether objects of different mass fall at the same rate, echoing Galileo's legendary experiment at the leaning tower of Pisa. Kasevich plans to toss two different kinds of rubidium atoms down his interferometer. The atoms differ slightly in mass because one contains more neutrons than the other.

Even with his giant interferometer set to begin experiments in 6 months, Kasevich is thinking bigger. A planned underground laboratory in the abandoned Homestake gold mine in Lead, S.D., has the physicist licking his lips. "We've been brainstorming about what we can do if we have a kilometer rather than 10 meters," he says.

Yet all interferometers on Earth, however deep, suffer from environmental noise, such as ocean tides and earthquakes. Physicists go to great extremes to shield their instruments from these effects, but as precision increases, environmental noise eventually drowns out results. "For the ultimate in precision we would like to consider space," says Savas Dimopoulos, a theoretical physicist at Stanford who hopes to use atom interferometry to detect gravitational waves radiating from pairs of black holes and other binary systems. He's working with Kasevich to perform the experiments on Earth, but a space experiment offers an even better chance to see the gravitational waves, which could provide a glimpse of the early universe. Any launch is at least a decade away, Dimopoulos says.

While atom interferometry probes the universe with growing meticulousness, another frontier of physics is taking a different approach to unlocking its secrets. Deep below ground crossing Switzerland's border with France, an army of physicists and engineers is readying the world's largest particle accelerator, the Large Hadron Collider (LHC), for a planned summer startup. With the LHC, physicists will smash protons together at speeds within a sliver of the speed of light, hoping to find new forms of matter.