After the Big Bang, matter and antimatter were created in equal amounts in the universe, yet through a long process of mutual annihilation, barely a trace of the latter remained. Everything around us: planets, stars, and even ourselves, is made up of what was left of matter, after a process that scientists from the LHCb experiment at CERN's Large Hadron Collider have just replicated for the first time with baryons, the particles that make up the majority of the matter in the observable universe.
"Understanding why we are made of matter and not antimatter (positive protons instead of negative antiprotons) is one of the key pieces in understanding our universe," points out Javier Fernández, a professor in the Physics department at the University of Oviedo and a member of the FPAUO High Energy Physics research group, in statements to the Science Media Centre (SMC).
According to some principles of physics, the cosmos should have destroyed itself when it was formed. The equal proportion of matter and antimatter should have instantaneously annihilated each other, so this tiny excess of matter that we call the universe puzzles scientists, who have been colliding particles at CERN for years.
Until now, this asymmetry between matter and antimatter had been found in another type of particles called mesons, composed of two quarks, which are the most basic building blocks of particles. The theoretical framework predicted that such asymmetry should also be observed in baryons, composed of three quarks, and present in the conventional matter of the universe and in any object on Earth, including the human body. However, it had not been discovered until now, in this experiment with a high Spanish participation, which has just been published in Nature.
"This is a pioneering result that confirms our theory about the fundamental laws of nature. It also represents a first step that can help us unveil a new physics. It is possible that the matter-antimatter asymmetry in the interactions of subatomic particles like baryons is responsible for the matter-antimatter asymmetry in the entire universe," points out Nuria Rius, director of the Institute of Corpuscular Physics (IFIC) at the University of Valencia, to the SMC.
Antimatter is not the absence of matter but its mirror image. Matter atoms are formed by positively charged nuclei orbited by negatively charged electrons. However, antimatter consists of negatively charged nuclei and positively charged electrons, known as positrons.
If the entire universe were made of antimatter, we would not notice any difference. The physical laws would still work the same. The problem arises when we encounter matter. If a man made of antimatter touched anything made of matter (air, a table, a person), the particles and antiparticles would mutually annihilate, releasing huge amounts of energy in the form of gamma rays. A single gram of antimatter encountering a gram of matter can release approximately twice the energy released by the Hiroshima bomb.
It is theoretically possible that in some corner of the universe there are galaxies or regions entirely made of antimatter. There is no evidence of this, but it is not completely ruled out either. So far, not enough antimatter has been detected to suggest that there are regions of the universe made of it. However, if they were to approach our matter universe, their mere presence would be catastrophic. If a 70-kilogram human of matter touched a 70-kilogram human of antimatter, both bodies would gradually annihilate as the particles touch. It would not be an instantaneous explosion, but a progressive annihilation from the point of contact, yet incredibly rapid, releasing 50 times the energy of the asteroid that ended the dinosaurs.