https://www.nature.com/articles/d41586- ... 1695831577Antimatter falls down, not up: CERN experiment confirms theory
Physicists have shown that, like everything else experiencing gravity, antimatter falls downwards when dropped.
This outcome is not surprising — a difference in the gravitational behaviour of matter and antimatter would have huge implications for physics — but observing it directly had been a dream for decades, says Clifford Will, a theoretician who specializes in gravity at the University of Florida in Gainesville. “It really is a cool result.”
Because gravity is much weaker than other ubiquitous forces such as electrostatic attraction or magnetism, separating it from other effects in the laboratory is a delicate affair, says Jeffrey Hangst, who leads of the ALPHA-g experiment at CERN, the particle physics laboratory near Geneva, Switzerland. “Gravity is just so bloody weak, you really have to be careful,” says Hangst, who is also a physicist at the University of Aarhus in Denmark. He and his collaborators reported the findings on 27 September in Nature1.
Similar experiments will aim to test whether gravity acts with the same strength on antimatter as it does on matter. Any tiny discrepancies could help to solve one of the biggest problems in physics — how the Universe came to be made almost exclusively of matter, even though equal amounts of matter and antimatter should have arisen from the Big Bang.
Antimatter in a can
After making a thin gas of thousands of antihydrogen atoms, researchers pushed it up a 3-metre-tall vertical shaft surrounded by superconducting electromagnetic coils. These can create a kind of magnetic ‘tin can’ to keep the antimatter from coming into contact with matter and annihilating. Next, the researchers let some of the hotter antiatoms escape, so that the gas in the can got colder, down to just 0.5 °C above absolute zero — and the remaining antiatoms were moving slowly.
The researchers then gradually weakened the magnetic fields at the top and bottom of their trap — akin to removing the lid and base of the can — and detected the antiatoms using two sensors as they escaped and annihilated. When opening any gas container, the contents tend to expand in all directions, but in this case the antiatoms’ low velocities meant that gravity had an observable effect: most of them came out of the bottom opening, and only one-quarter out of the top.
Black-hole jets begin to reveal their antimatter secrets
To make sure that this asymmetry was due to gravity, the researchers had to control the strength of the magnetic fields to a precision of at least one part in 10,000. This was perhaps their most remarkable feat, says Patrice Pérez, a physicist at the French Alternative Energies and Atomic Energy Commission in Gif-sur-Yvette, and the leader of GBAR, another of CERN’s antihydrogen experiments.
The results were consistent with the antiatoms experiencing the same force of gravity as hydrogen atoms would. The error margins are still rather large, but the experiment can at least conclusively rule out the possibility that antihydrogen falls upwards.
Continues on the link.
Pretty cool.
