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An Ultra-Precise Clock Shows How To Link the Quantum World With Gravity

lundi 25 octobre 2021, 18:43 , par Slashdot
Time was found to flow differently between the top and bottom of a single cloud of atoms. Physicists hope that such a system will one day help them combine quantum mechanics and Einstein's theory of gravity. From a report: The infamous twin paradox sends the astronaut Alice on a blazing-fast space voyage. When she returns to reunite with her twin, Bob, she finds that he has aged much faster than she has. It's a well-known but perplexing result: Time slows if you're moving fast. Gravity does the same thing. Earth -- or any massive body -- warps space-time in a way that slows time, according to Albert Einstein's general theory of relativity. If Alice lived her life at sea level and Bob at the top of Everest, where Earth's gravitational pull is slightly weaker, he would again age faster. The difference on Earth is modest but real -- it's been measured by putting atomic clocks on mountaintops and valley floors and measuring the difference between the two.

Physicists have now managed to measure this difference to the millimeter. In a paper posted earlier this month to the scientific preprint server arxiv.org, researchers from the lab of Jun Ye, a physicist at JILA in Boulder, Colorado, measured the difference in the flow of time between the top and the bottom of a millimeter-tall cloud of atoms. The work is a step toward studying physics at the intersection of general relativity and quantum mechanics, two theories that are famously incompatible. The new clock takes a fundamentally quantum system -- an atomic clock -- and intertwines it with gravity's pull. In the experiment, Ye's team used an optical lattice clock, a cloud of 100,000 strontium atoms that can get tickled by a laser. If the laser's frequency is just right, the electrons orbiting each atom will be excited to a higher, more energetic orbit. Because only a tiny range of laser frequencies motivate the electrons to move, measuring this frequency provides an extremely precise measurement of time. It's like a quantum grandfather clock, where the ticking comes from the oscillations of the laser light rather than the swing of a pendulum.

Read more of this story at Slashdot.
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