Although most physicists suspected it, no one had seen it until now. Antimatter responds to gravity in the same way that matter does. Which means that if we drop antimatter, it will fall downward, exactly like conventional matter. And no, it will not 'fall upwards, repelled by a sort of 'antigravitational force'. In a unique experiment, in fact, a team of researchers from the international collaboration ALPHA (Antihydrogen Laser Physics Apparatus), at the European CERN laboratory in Switzerland, has managed to observe the downward path followed by a series of individual antihydrogen atoms and has provided, after decades of doubts, a definitive answer: antimatter falls. The work, which has just been published in 'Nature', therefore rules out a supposed 'gravitational repulsion' as an explanation for the practical absence of antimatter in the Universe. "The success of the ALPHA collaboration," said Vyacheslav 'Slava' Lukin, program director of the National Science Foundation (NSF) Physics Division, "is a testament to the importance of teamwork across continents and scientific communities. Understanding the nature of antimatter can help us not only understand how our Universe came to be, but can also enable new innovations never before thought possible, such as positron emission tomography (PET) scans, which have saved many lives by applying our knowledge of antimatter to detect cancer cells and tumors in the body. The mystery of antimatter Everything that surrounds us, from ourselves to the walls of our house, the ground we walk on, the Earth, the Sun and all the stars and galaxies that we can see, is composed of just a handful of particles, such as protons, neutrons or electrons, which form atoms of oxygen, carbon, iron or any other element of the periodic table. All that matter emerged from the Big Bang 13.76 billion years ago, but at the same time, according to the most widespread theory, an identical amount of 'antimatter' must have emerged, the mirror image of ordinary matter (not to be confused with dark matter). ). But observations show us, stubbornly, a Universe made of only matter. So where is all the missing antimatter? No one has seen, nor expects to see, entire planets, or galaxies, made of antimatter. Although 'out there' antimatter should be just as abundant as what we see. Matter and antimatter are exactly the same, except for one thing: their electrical charges are opposite. Which means that if an electron (matter) has a negative charge, its corresponding antimatter particle, the positron, will have a positive charge. In the same way, for each proton of matter, with a positive charge, there corresponds an 'antiproton' of antimatter with a negative charge. And the same goes for any other particle. But that poses a problem. When a particle of ordinary matter (for example an electron) encounters its antiparticle (a positron) they annihilate in a small burst of energy. Therefore, if the Big Bang 'made' the same amount of one as the other, both matter and antimatter should have been completely annihilated, leaving… nothing. And yet, defying our understanding, there are the billions of galaxies and the trillions of stars and planets that make up our Universe. All made of matter and without the slightest trace of antimatter. Scientists call this problem 'baryogenesis'. One possible explanation, now ruled out by the new experiment, was that antimatter was gravitationally 'repelled' by ordinary matter during the Big Bang. Others maintain that, for some reason, during the Big Bang the symmetry between matter and antimatter was broken, so that more of the former arose than the latter. If that were so, the Universe we see would be the 'leftover' matter left after all the rest was annihilated. Does antimatter behave the same as matter? «Einstein's theory of general relativity – explains co-author Jonathan Wurtele, a plasma physicist at the University of California at Berkeley and a member of the ALPHA collaboration – says that antimatter should behave exactly like matter. Many indirect measurements indicate that gravity interacts with antimatter as expected, but until today's result, no one had really made a direct observation that could rule out, for example, antihydrogen moving up and not down in a field. gravitational". To carry out their experiment, the researchers generated a small amount of antimatter in their laboratory. «In general terms – continues Wurtele – we are producing antimatter to do an experiment like the Leaning Tower of Pisa, (supposedly done by Galileo in the 16th century to demonstrate an identical gravitational acceleration of two objects of similar volume but different mass launched simultaneously). "We are dropping the antimatter to see if it goes up or down." During the ALPHA experiment, the antihydrogen was contained inside a cylindrical vacuum chamber with a variable magnetic trap, called ALPHA-g. The scientists reduced the strength of the trap's upper and lower magnetic fields until the antihydrogen atoms could escape and the influence of gravity became evident. As each antihydrogen atom escaped from the magnetic trap, it touched the walls of the chamber above or below the trap and annihilated, which the scientists could detect and allowed them to count them. The researchers repeated the experiment more than a dozen times, varying the strength of the magnetic field at the top and bottom of the trap to rule out possible errors. They observed that when the weakened magnetic fields were precisely balanced at the top and bottom, about 80% of the antihydrogen atoms annihilated beneath the trap, a result consistent with how a conventional hydrogen cloud would behave under the same conditions. It was clear, therefore, that gravity caused the hydrogen to fall. «We have ruled out – concludes Wurtele – that antimatter is repelled by the gravitational force instead of attracted. "Which does not mean that there is no difference in the gravitational force on antimatter, although only a more precise measurement will tell that." Now, researchers in the ALPHA collaboration will continue to investigate the nature of antihydrogen. And in addition to refining their measurement of the effect of gravity, they are also studying how antihydrogen interacts with electromagnetic radiation using spectroscopy. MORE INFORMATION news Yes Closer to knowing if there is life: they finally find a source of carbon on the moon Europe news No Spanish researchers find fairy circles all over the world «If antihydrogen were in some way different from hydrogen –he claims the researcher - would be something revolutionary because physical laws, both in quantum mechanics and gravity, say that the behavior should be the same. However, you can't be sure until you do the experiment.
