The mystery of antimatter

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The mystery of antimatter
The mystery of antimatter
Anonim

Scientists call this baryon asymmetry. Its reasons are unclear and require an explanation.

Antimatter

Everything we come into contact with in our life is made of matter. The cup that we hold in our hand consists of molecules, molecules - of atoms, atoms, contrary to their name ("atom" in translation from Greek means "indivisible") - of electrons, protons and neutrons. The last two are called "baryons" by scientists. They can be divided further, into quarks, and maybe even further, but for now we will dwell on this. Together they form matter.

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As all our readers know, matter has an antipode - antimatter. When they come into contact, they annihilate with the release of a very large energy - they annihilate. According to the calculations of physicists, a piece of antimatter the size of a brick, hitting the Earth, can cause an effect akin to the explosion of a hydrogen bomb. In all other respects, the antipodes are similar: antimatter has mass, the laws of physics fully apply to it, but its electric charge is opposite. It is negative for an antiproton, and positive for a positron (antielectron). And also antimatter practically does not occur in the reality around us.

The search for antimatter

Or is it somewhere there? There is nothing impossible in such an assumption, but we live in the world, although we cannot shake hands with our antipodes. It is quite possible that they also live somewhere.

Probably all galaxies observed today are composed of ordinary matter. Otherwise, their boundaries would be a zone of almost continuous annihilation with the surrounding matter, it would be visible from afar. Earth observatories would register energy quanta formed during annihilation. Until this happens.

The evidence of the presence in the Universe of noticeable amounts of antimatter could be the discovery somewhere in space (on Earth, due to the high density of matter, it is clearly useless to look for antihelium nuclei). Two antiprotons, two antineutrons. The antiparticles that make up such a nucleus are regularly produced in collisions of high-energy particles in terrestrial accelerators and naturally when matter is bombarded by cosmic rays. Their discovery tells us nothing. But antihelium can be formed in the same way if four of its constituent particles are simultaneously born in one place. This cannot be called completely impossible, but such an event in the entire Universe happens about once every fifteen billion years, which is quite comparable with the time of its existence.

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Therefore, the detection of antihelium may well be regarded, if not as a greeting from the antipodes, then as evidence that somewhere in the depths of space, a piece of antimatter of decent size is floating. So it flew from there.

Alas, repeated attempts to search for antihelium in the upper layers of the earth's atmosphere or on the approach to it have not yet brought success. Of course, this is the case when "the absence of traces of gunpowder on the hands proves nothing." It may well be that it was just very far to fly (on the order of billions of light years), and getting into a small detector on a small planet is even more difficult. And for sure, if the detector were more sensitive (and more expensive), our chances of success would be higher.

Anti-stars, if they happened to be in nature, in the course of thermonuclear reactions would generate the same flux of antineutrinos, like ordinary stars - the flux of their antipodes. The same antineutrinos should be formed during antisupernova explosions. So far, neither one nor the other has been discovered, but it should be noted that neutrino astronomy is taking its first steps in general.

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In any case, we do not yet have reliable information about the existence of any noticeable amounts of antimatter in the Universe.

This is good and bad at the same time.It is bad because, according to modern concepts, both matter and antimatter were formed in the first moments after the Big Bang. Subsequently, they annihilated, giving rise to cosmic relic radiation. The number of photons in it is very large, it is about a billion times greater than the number of baryons (i.e., protons and neutrons) in the Universe. In other words, once, at the beginning of time, the substance in the Universe turned out to be one billionth more than antimatter. Then all the "superfluous" disappeared, annihilated, and one billionth share remained. The result is what is called baryon asymmetry in the special literature.

For physicists, imbalance is a problem because it needs to be explained somehow. At least in the case of objects that in all other respects behave symmetrically.

And for us (including physicists) this is good, because with the same amounts of matter and antimatter, complete annihilation would occur, the Universe would be empty, and there would be no one to ask questions.

Sakharov's terms

Scientists realized the existence of a large cosmological problem sometime in the middle of the 20th century. The conditions under which the Universe becomes the way we see it were formulated by Andrei Sakharov in 1967 and since then have been a "common place" of thematic literature, at least in Russian and English. In a highly simplified form, they look like this.

First, under some conditions that probably existed in the early Universe, the laws of physics still work differently for matter and antimatter.

Secondly, in this case the baryon number may not be preserved, i.e., the number of baryons after the reaction is not equal to that before it.

Thirdly, the process must proceed in an explosive manner, that is, it must be non-equilibrium. This is important, because in equilibrium the concentrations of substances tend to equalize, and we need to get something different.

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This is where the generally accepted part of the explanation ends, then, and after half a century, hypotheses dominate. The most authoritative one at the moment connects the incident with the electroweak interaction. Let's take a closer look at her.

Boiling space

To explain what happened to our matter, we will have to strain our imagination and imagine that there is a certain field in the Universe. We do not yet know anything about its existence and properties, except that it is associated with the distribution of matter and antimatter in space and is to some extent similar to the temperature we are accustomed to, in particular, it can take larger and smaller values, up to a certain level, which can be likened boiling point.

Initially, matter in the universe is in a mixed state. It is very "hot" around - the quotes could be omitted here, since the usual temperature is also very high, but we are talking about its imaginary analogue. This analogue "boils" - the value is maximum.

As the space expands, “drops” begin to condense from the original “vapor”, in which it is “cooler”. So far, everything looks exactly the same as with water - if the superheated steam is in a vessel, the volume of which increases rather quickly, then adiabatic cooling occurs. If it is strong enough, then some of the water will fall out as a liquid.

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Something similar happens with matter in space. As the volume of the Universe grows, the number and size of the "drops" increase. But then something begins that has no analogies in the world we are used to.

The conditions for penetration of particles and antiparticles into the "drops" are not the same; it is a little easier for particles to do this. As a result, the initial equality of concentrations is violated, in the condensed "liquid" there is a little more substance, and in the "boiling phase" - its antipode. In this case, the total number of baryons remains unchanged.

And then, in the "boiling phase", quantum effects of interacting electroweak fields begin to operate, which, it seems, should not change the number of baryons, but in reality equalize the number of particles and antiparticles. Strictly speaking, this process takes place in “drops” too, but there it is less effective. Thus, the total number of antiparticles is reduced. This is written shortly and, of course, very simplified, in fact, everything is much more interesting, but now we will not go into the theory deeply.

Two effects turn out to be key to explain the situation. The quantum anomaly of electroweak interactions is an observed fact, it was discovered back in 1976. The difference in the probability of particles penetrating into the condensation zone is a calculated fact and, therefore, hypothetical. The field itself, which "boils" and then cools, is not yet detected. When forming the theory, it was assumed that this is the Higgs field, but after the discovery of the famous boson, it turned out that it had nothing to do with it. It is possible that its opening is still waiting in the wings. Or maybe not - and then cosmologists will have to invent other explanations. The universe has been waiting for this for fifteen billion years, it can wait another.

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