The atoms that make up ordinary matter fall down, so do antimatter atoms fall up? Do they experience gravity the same way as ordinary atoms, or is there such a thing as antigravity?
These questions have long intrigued physicists, says Joel Fajans of the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), because "in the unlikely event that antimatter falls upwards, we'd have to fundamentally revise our view of physics and rethink how the universe works."
So far, all the evidence that gravity is the same for matter and antimatter is indirect, so Fajans and his colleague Jonathan Wurtele, both staff scientists with Berkeley Lab's Accelerator and Fusion Research Division and professors of physics at the University of California at Berkeley -- as well as leading members of CERN's international ALPHA experiment -- decided to use their ongoing antihydrogen research to tackle the question directly. If gravity's interaction with anti-atoms is unexpectedly strong, they realized, the anomaly would be noticeable in ALPHA's existing data on 434 anti-atoms.
The first results, which measured the ratio of antihydrogen's unknown gravitational mass to its known inertial mass, did not settle the matter. Far from it. If an antihydrogen atom falls downward, its gravitational mass is no more than 110 times greater than its inertial mass. If it falls upward, its gravitational mass is at most 65 times greater.
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