Scientists from the CERN ALPHA collaboration have presentedthe first direct evidence of how antimatter atoms interact with gravity. The study, which publishesNature Communications, has focused on measuring thegravitational mass of antihydrogen, the simplest neutral antimatter atom.
After measuring its gravitational mass –the attractive force in a gravitational field– and seeing its ratio with respect to its inertial mass –resistance to change in speed–, physicists have verified thatif an antihydrogen atom falls downward, its gravitational mass is no more than 110 times greater than its inertial mass. But if it fell upward, its gravitational mass is at most 65 times greater. Although it is not yet clear in which direction it “falls”, in any case what the study shows is that it is already possible to measure the gravity of antimatter.
According to Marcelo Baquero-Ruiz, from the University of California at Berkeley (USA) and co-author of the work, there are many arguments that suggest that matter and antimatter should attract and behave in the same way. However, no one has had a chance to experimentally test this claim until now. “But questions remain unresolved: Will antimatter fall up or down? Or is it perhaps attracted to matter but with a different acceleration?” He wonders. So, for example, in the unlikely event that antimatter fell upward, experts say we would have to radically revise our view of physics and rethink how the universe works.
Current theoretical arguments predict that hydrogen and antihydrogen atoms have the same mass and must interact under gravity in the same way.If an atom is released, it should experience a downward force whether it is made of matter or antimatter.
“The ALPHA device can trap antihydrogen atoms and then release them on purpose,” clarifies Jeffrey Hangst, the ALPHA spokesman, to explain the technique he has followed. “We used our position-sensitive annihilation detector to see if we could observe the influence of gravity on these released atoms.” Scientists are confident that when the experiment is resumed in 2014 with an updated antimatter trap, dubbed ALPHA-2, further progress will be made. In addition, CERN is preparing other experiments, such as AEgIS and GBAR, to continue measuring how gravity affects antihydrogen.
