There is almost no antimatter in the universe. Why?

When we look at the Universe, at all its planetsand stars, galaxies and clusters, gas, dust, plasma, we see the same signatures everywhere. We see lines of atomic absorption and emission, we see that matter interacts with other forms of matter, we see star formation and death of stars, collisions, X-rays and much more. There is an obvious question that requires an explanation: why do we see all this? If the laws of physics dictate the symmetry between matter and antimatter, the Universe that we observe should not exist.

But we are here, and no one knows why.

Why is there no antimatter in the universe?

Think about these two contradictory, at first glance, facts:

  • Every interaction between particles wehave ever been observed at any energy, never created and did not destroy one particle of matter, without creating or destroying an equal number of particles of animatter. Physical symmetry between matter and antimatter is very strict, because:
    • each time we create a quark or lepton, we also create antiquark and antilepton;
    • each time a quark or lepton is destroyed, an antiquark or antilepton is also destroyed;
    • created or destroyed leptons and antileptonsmust be in balance throughout the family of Letpons and each time a quark or lepton interact, collide or decay, the total number of quarks and leptons at the end of the reaction (quarks minus antiquark, leptons minus antileptons) should be and will be the same as it was at the beginning .

    The only way to change the amount of matter in the Universe also implied a change in the amount of antimatter by the same amount.

    And yet, there is a second fact.

  • When we look at the Universe, at all the stars,galaxies, gas clouds, clusters, superclusters, and large-scale structures, it seems that all this is made up of matter, not antimatter. Everywhere and everywhere, where antimatter and matter are found in the Universe, a fantastic release of energy occurs due to the annihilation of particles.
  • But we see no signs of destruction.antimatter substances on a large scale. We see no indication that some of the stars, galaxies or planets that we see are made of antimatter. We do not see the characteristic gamma rays, which one would expect to see if antimatter would collide with matter and annihilate. Instead, everywhere we see only matter, wherever you look.

    And it seems impossible. On the one hand, there is no known way to make more matter than antimatter, if we turn to particles and their interaction in the Universe. On the other hand, everything that we see is definitely composed of a substance, not antimatter.

    In fact, we observed the annihilation of matter andantimatter in some extreme astrophysical conditions, but only near hyper-energy sources that produce matter and antimatter in equal quantities - black holes, for example. When antimatter collides with matter in the universe, it produces gamma rays of very specific frequencies that we can then detect. The interstellar intergalactic medium is full of material, and the complete absence of these gamma rays is a strong signal that there is never a large amount of antimatter particles, since then a signature of matter-antimatter would be detected.

    If you throw one bit of antimatter into ourgalaxy, it will last about 300 years before it is destroyed by a particle of matter. This restriction tells us that in the Milky Way the amount of antimatter cannot exceed the value of 1 particle per quadrillion (1015), relative to the total amount of matter.

    On a large scale - satellite scalesgalaxies, large galaxies of the size of the Milky Way and even clusters of galaxies - the restrictions are less strict, but still very strong. Observing distances from several million light years to three billion light years, we observed a lack of X-rays and gamma rays, which could indicate the annihilation of matter and antimatter. Even on a large cosmological scale, 99.999% of what exists in our Universe will definitely be represented by matter (as we are), and not by antimatter.

    How did we find ourselves in such a situation thatThe universe consists of a large amount of matter and contains almost no antimatter, if the laws of nature are absolutely symmetrical between matter and antimatter? Well, there are two options: either the universe was born with more matter than antimatter, or something happened at an early stage, when the universe was very hot and dense, and gave rise to the asymmetry of matter and antimatter, which was not there.

    The first idea to check scientifically without recreatingthe whole universe will fail, but the second is very convincing. If our Universe somehow created an asymmetry of matter and antimatter where it was not originally, then the rules that worked then will remain unchanged today. If we are smart enough, we can develop experimental tests that reveal the origin of matter in our Universe.

    In the late 1960s, physicist Andrei Sakharov defined three conditions necessary for baryogenesis or the creation of more baryons (protons and neutrons) than anti-baryons. Here they are:

  • The universe must be a non-equilibrium system.
  • It must contain C and CP violation.
  • There must be interactions that violate the baryon number.
  • The first is simple because it is expanding andthe cooling Universe with unstable particles in it (and antiparticles), by definition, will be out of equilibrium. The second is also simple, since C-symmetry (replacement of particles with antiparticles) and CP-symmetry (replacement of particles with specularly reflected antiparticles) are violated in a multitude of weak interactions involving strange, enchanted and beautiful quarks.

    The question remains how to break the baryon number. Experimentally, we observed that the balance of quarks to antiquarks and leptons to antileptons is clearly preserved. But in the Standard Model of particle physics there is no explicit conservation law for any of these quantities separately.

    It takes three quarks to make a baryon, sofor every three quarks we assign a baryon number (B) 1. In the same way, each lepton will receive a lepton number (L) 1. Antiquarks, anti-baryons and anti-blips will have negative numbers B and L.

    But according to the rules of the Standard Modelonly the difference between baryons and leptons. Under the right circumstances, you can not only create additional protons, but also electrons to them. The exact circumstances are unknown, but the Big Bang gave them the opportunity to materialize.

    The very first stages of the universedescribed by incredibly high energies: high enough to create every known particle and antiparticle in large quantities using Einstein's famous formula E = mc2. If the creation and destruction of particles works as we think, the early Universe should have been filled with an equal number of particles of matter and antimatter, which turned into each other, because the available energy remained extremely high.

    With the expansion and cooling of the universeunstable particles, once created in abundance, will collapse. If the right conditions are met - in particular, the three conditions of sugars - this can lead to an excess of substance over antimatter, even if it was not originally there. The challenge for physicists is to create a viable scenario, consistent with observations and experiments, which can give you a sufficient excess of substance over antimatter.

    There are three main possibilities for the occurrence of this excess substance over antimatter:

    • New physics in the electroweak scale cansignificantly increase the number of C- and CP-violations in the Universe, which will lead to the asymmetry between matter and antimatter. The interactions of the Standard Model (through the sphaleron process), which violate B and L individually (but retain B - L), can create the necessary volumes of baryons and leptons.
    • New neutrino physics at high energies, onwhich the universe hints at us could create a fundamental asymmetry of leptons: leptogenesis. Sphalerone preserving B - L could then use lepton asymmetry to create baryon asymmetry.
    • Or baryogenesis on the scale of the theory of great unification, if new physics (and new particles) exist on the scale of great unification, when the electroweak force combines with the strong.

    These scenarios have common elements, so let's look at the last one, just for the sake of example, to understand what could have happened.

    If the theory of great unification is correct,to be new, super-heavy particles, called X and Y, which have both baryon-like and lepton-like properties. Their partners from antimatter must also be: anti-X and anti-Y, with opposite numbers B - L and opposite charges, but with the same mass and lifetime. These particle-antiparticle pairs can be created in large quantities at sufficiently high energies to subsequently decay.

    So we fill the universe with them, and then theybreak apart. If we have C and CP violations, there may be slight differences in how the particles and antiparticles decay (X, Y and anti-X, anti-Y).

    If the X-particle has two ways: decay into two top quarks or two anti-bottom quarks and a positron, then anti-X must go through two appropriate ways: two anti-top quarks or a bottom quark and an electron. There is an important distinction that is allowed when C- and CP are violated: X can more likely fall into two upper quarks than anti-X into two anti-upper quarks, while anti-X is more likely to disintegrate into the lower quark and electron than X - on the anti-top quark and positron.

    With a sufficient number of pairs and decay in this way, you can easily get an excess of baryons over antibaryons (and leptons over antileptons) where it was not there before.

    This is just one example illustrating ouridea of ​​what happened. We started with a completely symmetrical Universe, obeying all the known laws of physics, and with a hot, dense, rich state filled with matter and antimatter in equal quantities. Using the mechanism that we have yet to determine, subject to the three conditions of Sakharov, these natural processes ultimately created an excess of substance over antimatter.

    The fact that we exist and consists of matterindisputable; the question is why our Universe contains something (matter), and not nothing (after all, matter and antimatter were equally divided). Perhaps in this century we will find the answer to this question.

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