For the first time, scientists have observed antimatter particles – the mysterious twins of the visible matter around us – falling under the influence of gravity, European physics laboratory CERN announced Wednesday. The experiment was hailed as “a major milestone”, even though most physicists had anticipated the outcome and it was predicted by Albert Einstein’s 1915 theory of relativity. This definitively rules out the possibility of gravity pushing antimatter upward – a discovery that would shake up our fundamental understanding of the universe. About 13.8 billion years ago, the Big Bang would have created an equivalent amount of matter – which is what everything you can see is made of – and antimatter, its equivalent but opposite counterpart .
However, there is virtually no antimatter in the universe, which gives rise to one of the biggest mysteries in physics: what happened to all the antimatter? “Half the universe is missing,” said Jeffrey Hangst, a member of the ALPHA collaboration at CERN in Geneva, who leads the new experiment. “In principle, we could build a universe – everything we know – using only antimatter, and it would work the same way,” he told AFP. Physicists believe that matter and antimatter met and almost completely destroyed each other after the Big Bang. However, matter now makes up nearly 5% of the universe – the rest is made up of dark matter and the even less well understood dark energy – while antimatter has disappeared.
One of the main outstanding questions about antimatter is whether gravity causes it to fall like normal matter. While most physicists think this is the case, a few hypothesize the opposite. The falling apple inspired Isaac Newton’s research on gravity. But if this apple was made of antimatter, would it fly into the sky? And if gravity really repels antimatter, that could mean impossible things like perpetual motion machines are possible.
“So why don’t we put some down and see what happens?” Hangst said. He compared this experiment to Galileo’s famous – though probably apocryphal – 16th-century demonstration that two balls of different masses dropped from the Leaning Tower of Pisa would fall at the same speed. But this experiment – the result of 30 years of antimatter research at CERN – is “a bit more complicated” than Galileo’s experiment, Hangst said. One problem is that antimatter is virtually non-existent outside of rare, short-lived particles in space. However, in 1996, scientists at CERN created the first antimatter atom, antihydrogen.
Another challenge is that because matter and antimatter have opposite electrical charges, as soon as they meet, they will destroy each other in a violent flash of energy that scientists call annihilation. To study the effects of gravity on antimatter, the ALPHA team built a 25 cm long bottle placed at the end of the bottle, with magnets on top and bottom. Late last year, scientists placed about a hundred very cold antihydrogen atoms into this “magnetic trap” called ALPHA-g. By reducing the power of the two magnets, antihydrogen particles – which are bouncing around at 100 meters per second – can escape through both ends of the bottle. Then, the scientists simply counted the amount of annihilated antimatter at each end of the bottle. About 80 percent of the antihydrogen escapes from the bottom, similar to how bouncing hydrogen atoms would behave if they were in a bottle.
This result, published in the journal Nature, shows that gravity causes antimatter to fall, just as predicted by Einstein’s theory of relativity in 1915. In more than a dozen experiments, CERN scientists changed the intensity strength of the magnet, observing the effect of gravity on antimatter at different rates. Although the experiment rules out that gravity would cause antihydrogen to rise, Hangst emphasized that it does not prove that antimatter behaves exactly like regular matter. “That’s our next mission,” he said. Teacher. Elazar Sarid of the physics department at Ben-Gurion University of the Negev, an Israeli member of the ALPHA team, said the results were “just the beginning” and scientists would now work to improve the accuracy. accuracy of measurements for the next series of studies. experiment. . Marco Gersabeck, a physicist who works at CERN but was not involved in the ALPHA study, said this was an “important milestone”. But this marks “just the beginning of an era” of more precise measurements of the effects of gravity on antimatter, he told AFP. Other efforts to better understand antimatter include using CERN’s Large Hadron Collider to study strange particles called beauty quarks. And there’s an experiment on the International Space Station trying to capture antimatter in the form of cosmic rays. But for now, exactly why the universe is filled with matter but not antimatter “remains a mystery,” says physicist Harry Cliff. Since the two would have destroyed each other at the beginning of the universe, “the fact that we exist suggests that there is something going on that we don’t understand,” he added. Times of Israel staff contributed to this report.
source: https://www.nature.com/articles/s41586-023-06527-1