Antimatter, one of the great mysteries of the universe, continues to make leaps and bounds towards antimystery. Isaac Newton's historic work on Earth's gravity was allegedly inspired by an apple falling on his head from a tree. But what about an anti-apple made of antimatter? Would it fall the same way if it existed? According to Albert Einstein's theory of general relativity, yes, but it has taken us a century to prove it.
Just as Galileo Galilei climbed 500 years ago to the tower of Pisa to demonstrate that two spheres of different mass reached down at the same time, and not before the heaviest, as one might suppose, scientists from the European Organization for Nuclear Research (CERN) dropped a hundred molecules of antihydrogen before the possibility that antimatter did not behave in the same way as matter, and instead of falling to the ground they were repelled upwards.
The result of the experiment has been that antimatter has no antigravity, so that antihydrogen behaved exactly like hydrogen, and descended the metaphorical tower of Pisa elaborated by international researchers of the Antihydrogen Laser Physics Apparatus (ALPHA) of the CERN of Switzerland, in collaboration with more than a dozen countries and private institutions. including the U.S. National Department of Science.
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CERN announces the discovery of new "exotic" particles
- Writing: EFE Geneva
CERN announces the discovery of new "exotic" particles
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The theoretical physicist who moved from CERN to cancer research
- Writing: CRISTINA G. LUCIO Madrid
The theoretical physicist who moved from CERN to cancer research
The discovery, published today in Nature, serves to rule out that gravitational repulsion is the reason why almost everything in the universe is matter, and antimatter has not gone elsewhere expelled by gravity. "In physics, you don't really know something until you look at it," says ALPHA spokesman Jeffrey Hangst. "It is a milestone in the study of antimatter, which still baffles us by its apparent absence in the Universe."
Our bodies, the Earth, and almost everything scientists know about the universe are overwhelmingly composed of regular matter, with protons, neutrons, and electrons, as well as atoms of oxygen, carbon, iron, and other elements from the periodic table. Antimatter is neither dark nor invisible matter. In fact, it is generated in places as inhospitable as in the disintegration of potassium inside a banana. It is simply a twin of matter but with some opposite properties. For example, while protons are positively charged, antiprotons are negatively charged. Just as antielectrons (also known as positrons) are positive while electrons are negative.
The laws of physics predict that antimatter should exist in the universe in amounts roughly equal to those of normal matter, yet it is barely present, a conundrum scientists call baryogenesis. One possible explanation was that antimatter had been gravitationally repelled by regular matter during the Big Bang, but this new discovery has shattered this hypothesis.
Conceptual illustration of the Big Bang.RICHARD JONES
"Einstein's theory of general relativity says that antimatter should behave exactly like matter," said Jonathan Wurtele, a plasma physicist at the University of California, Berkeley and a member of ALPHA. "Many indirect measurements indicated that gravity interacted with antimatter, but until today's result, no one had really made a direct observation that could rule out, for example, that antihydrogen moved up and not down in a gravitational field."
The most interesting thing about antimatter, and what makes it useful at the moment, for example in medicine, is that as soon as it touches matter, it explodes, transforming itself into energy, specifically photons, in a reaction so powerful that scientists call annihilation. That is, if the anti-apple fell on our heads we would both end up annihilated.
"For a given mass, such annihilations are the densest form of energy release we know," said Joel Fajans, a ALPHA collaborator and plasma physicist at the University of California, Berkeley. From coal you can get 30,000 joules of energy per gram, from nuclear 80,000 million joules per gram, but from the contact between matter and antimatter we speak of 90 billion joules per gram. A fact that inspired the photon torpedoes of the fictional Star Trek, and whose reality is that it would take only 10 milligrams of antimatter to send a ship to Mars.
The problem is that right now it costs us more energy to create antimatter than it could give us. In fact, it is the most expensive substance in the known universe, with an estimated cost of about 65,000 million euros per gram. Because of this, some NASA studies are seriously considering trying to collect the antimatter that is naturally generated in Earth's Van Allen Belts, caused by the solar wind in Earth's magnetosphere.
CERN particle accelerator in Switzerland.EFE
"Understanding the nature of antimatter can help us not only understand how our universe arose, but also enable new innovations not thought possible, such as positron emission tomography (PETs) that have saved many lives, by applying our knowledge about antimatter to detect cancer cells and tumors in the body." says Vyacheslav Slava Lukin, program director of the Physics Division of the US Department of Science (NSF).
The production of antimatter, in addition to consuming enormous amounts of energy, is very inefficient, around only 1% of the particles created; and it is also destroyed when it comes into contact with matter, which makes it very complicated to preserve it. "It's taken us 30 years to learn how to make this antiatom, retain it and control it well enough that we can drop it in a way that is sensitive to the force of gravity," said Jeffrey Hangst.
For the ALPHA experiment, antihydrogen was contained inside a tall cylindrical vacuum chamber with a variable magnetic trap, called ALPHA-g. The scientists then reduced the strength of the trap's upper and lower magnetic fields until the antihydrogen atoms were able to escape, and fell as a result of gravity.
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.
- Articles Ricardo F. Colmenero