An experiment confirms that antimatter falls downwards

In 1928, Paul Dirac developed an equation that showed a universe alien to our everyday intuitions. The British physicist, only 25 years old, presented his theory of the electron, an attempt to harmonize the quantum world with Einstein’s theory of special relativity and explain the behavior of these particles at high speed. The formula, instead of including two characteristics of the electron, the spin that determines whether it spins clockwise or counterclockwise, contained four. If this equation described reality, and for Dirac its mathematical beauty proved that it did, it was necessary that another type of electrons existed in the world, identical to the known ones, but with a positive charge.

It was the theoretical birth of antimatter and antigalaxies and antiplanets could exist in the cosmos, but no one had ever seen a positron. That changed in 1932, when Carl Anderson of the California Institute of Technology first caught signals from these particles among cosmic rays passing through a cloud chamber. Over time it was seen that all particles had an antiparticle associated with them and both Dirac and Anderson received the Nobel Prize in Physics.

The traces of antimatter found among cosmic rays did not leave physicists calm. According to the Big Bang theory, when the universe inflated from an infinitely dense and small point to light the cosmos, an identical amount of matter and antimatter emerged. That would have created a problematic situation for us, because every time a particle met its antiparticle it would disintegrate in a burst of energy release. Without bricks to build, the formation of galaxies or antigalaxies or of humans or antihumans would not have been possible. The origin of this violation of the initial symmetry has been sought in many places, also in a different behavior under gravity.

Although antimatter had not been discovered when Albert Einstein published the General Theory of Relativity, his predictions, which have been passing exams for more than a century, implied that all masses, regardless of their internal structure, react the same to gravity. Today, an article published in the magazine Nature once again agrees with the German scientist after proving that antimatter, like matter, falls downwards into the gravitational hole that the mass of the Earth generates in the space-time fabric.

Those responsible for this discovery, an international group of scientists, have used the antimatter factory from CERN to make hydrogen antiatoms and then test whether they react to gravity in the same way as the atoms of this gas. With two accelerators, they generated positrons, on the one hand, and antiprotons, on the other. Then, they gathered them in a kind of magnetic bottle 25 centimeters high, in an experiment called ALPHA-g, in which they are trapped and can join together to form hydrogen antiatoms. Once they had accumulated enough of them, around 100, and brought them to a temperature close to absolute zero so that they would move more slowly, they opened the trap above and below and waited to see through which of those cracks the most antimatter escaped. . When this test is done, 88% of the hydrogen atoms come out through the lower hole, and the authors of the experiment saw that with the atoms the amount was similar.

As the authors of the work themselves acknowledge, their results do not surprise anyone. “If you walk the halls of this department and ask physicists, they will all tell you that this result is not at all surprising, that is the reality,” said Jonathan Wurtele, a theoretical physicist at the University of California at Berkeley ( USA) who, together with Joel Fajans, from the same institution, proposed this type of experiment more than a decade ago. However, in a note from his institution, he added that, “most of them will also say that the experiment had to be done because you can never be sure.” “Physics is an experimental science. “You don’t want to be so stupid that you don’t do an experiment that explores possible new physics because you thought you knew the answer, and then it turns out it was something different,” he concluded.

Ruling out that there is no repulsive gravity between the Earth and antimatter and that antiapples would not fall upwards, once again proves Einstein right, but deepens the mystery of the absence of antiparticles or the fact of our existence. Some hypotheses seek the explanation for the saving imbalance in a quantum fluctuation that destroyed the balance and made the world possible. Others test the role of neutrinos in this battle. These particles, which almost do not interact with anything, oscillate between their three varieties, and it is proposed that the differences in the oscillation of neutrinos and antineutrinos in those initial moments after the Big Bang could have given matter the victory. In the answers to questions like these, we can find the paths to go beyond the enormous successes of physics at the beginning of the 20th century, general relativity to explain gravity and quantum and its ramifications to understand the strange functioning of the subatomic world. .

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