Simply put, antimatter is like a mirror image of matter . It is easy to understand what a reflection is and it takes very little time for us to be able to distinguish it from the real object: the left and right sides of the image are reversed from the original; other than that, image and object are exactly the same.
In the case of antimatter, the same thing happens, but everything is a little more complicated. To understand it, we must bear in mind that physicists distinguish one particle from another in the same way that we distinguish one fruit from another, by its properties: size, color, smell and taste. In the case of subatomic particles we have to refer to characteristics such as mass, charge, angular momentum and magnetic moment . The first two are easy to understand, but the second two are not. By fixing ideas and simplifying too much, we can assimilate angular momentum to rotation and the magnetic moment at which the particles, supposedly spherical, behave like the great magnet that is the Earth, with a magnetic north and south pole.
So what is an antielectron? First, it has the charge reversed, it is positive rather than negative. And the same thing that happens when we see a ball spin in the mirror, its ‘rotation’, the angular momentum, will also be reversed. The same goes for the proton. In this way an antiproton and an antielectron – also called a positron – form the antihydrogen atom . But the most important characteristic of antimatter is certainly amazing: when a particle of matter and its antimatter image come into contact, they are annihilated. All of its mass is converted into energy, the quantity of which is given by what is perhaps the most famous formula in physics, E = mc 2 . Ultimately, the annihilation of a single gram of antimatter would produce as much energy as that released by the bomb that destroyed Hiroshima.
For reasons that are still unknown, the universe was born with a little more matter than antimatter
On the other hand, it is evident that in our universe, or at least in the universe that we know, there is no antimatter. It was detected for the first time in 1932 by a young 27-year-old English professor, Carl Anderson , who studied cosmic rays, that shower of particles and photons that reach the Earth and that occurs both in the Sun and in the tremendous deflagrations that sometimes they happen in stars and galaxies. Anderson did not know that one of the giants of theoretical physics, Paul Dirac, had predicted the existence of antimatter three years earlier.
Now, if there is only matter in our universe, where does antimatter come from? Here we return to Einstein. If matter and antimatter are converted into energy, into photons, this can also be reconverted. That is, a photon with sufficient energy can become an electron and a positron, or a proton and an antiproton ; always in a particle and its corresponding antiparticle. That is what happens in cosmic rays. Antimatter is produced inside particle accelerators as a by-product of collisions in them.
But the main problem with antimatter is another, and it is one of the greatest challenges facing the cosmological model of the Big Bang. With the explosion that marked the beginning of the universe, as much matter as antimatter had to be created. Now, if this 50-50 had been exact we would not be here to tell it because all matter would have been completely annihilated with its corresponding antimatter. Faced with such a problem, there are only two solutions: first, that our universe is divided into two parts, one with stars and planets and the other with antistars and antiplanets. This option has a serious drawback. The boundary between both universes would be visible in the form of gamma rays by the continuous explosions, and this is not observed. The other alternative is to assume that 50-50 is not exact, but that there was a very small excess of matter. But the theory tells us that this did not happen, then there is something wrong with it . And although there are different explanations for this asymmetry, no one has provided a convincing explanation.
Which does not hold a certain irony: the Standard Model of Particle Physics, the theory that best describes the behavior of matter at the microscopic level, says that we should not be here. But we are.
