Saharov and cosmology

Everyone knows Andrei Dmitrievich Sakharov as the father of a hydrogen bomb and as a public figure. Much fewer people know about his contribution to fundamental science. This is not to say that this contribution is huge in quantitative terms - he wrote an order of magnitude less scientific articles than, for example, Ya. B. Zeldovich. However, in a number of his articles, he greatly ahead of the time, raised questions and gave answers that, after many years, determined the directions where the masses of the researchers poured. In this series of publications, we talk about two pioneering articles that influenced the development of cosmology. An interesting feature of both articles: the correct approach and the correct conclusions were made with the involvement of assumptions that are actually not realized in nature, which was understood later. The newspaper format does not allow to illuminate both articles in one issue, so we give two publications in different issues of the newspaper. Let's start with a later article on the Baryon asymmetry of the Universe.

Why does our world consist only of substance (without anti -ity), and why are the substances so few?

(“Violation of SR-invitations. Co-asymmetry and bario asymmetry of the Universe”, A. D. Sakharov, ZhETF, Letters to the editor, 1967, v. 5, issue 1)

In our galaxy, there is no anti -ity in noticeable quantities. Otherwise, it would make itself felt, annihilating with the substance. It is also not in the local group of galaxies. In general, we can say that the antimatter in the form in which the substance is located is practically absent in the observed universe. In any case, it is theoretically impossible to explain the division of matter and anti -ity into the "islands" in the universe. Therefore, there is a consensus that the universe contains only a substance (with the exception of a small part of cosmic rays that is born during interactions of high -energy particles). Thus, our universe is asymmetric, which we should be grateful: we are not threatened with a meeting and annihilation with antimatter.

There is another remarkable and in a sense amazing fact. For each baron (protons along with neutrons and other, unstable particles consisting of three quarks are called ramers) in the universe there are more than a billion photons of relict radiation. Why is this fact amazing? To answer this question, you need a brief excursion into thermodynamics at the level of the first year of the institute.

In the first moments of the existence of the Universe, the temperature was so high that the kinetic energy of the barions and other particles of the cosmic environment was much more than their mass of peace. In the clashes of energetic particles, Barion-antibarion (in the modern language is more correct to say quark-antifated) couples were intensively born. In this regard, the rams were not much different from photons, and, according to the laws of thermodynamics, their number per volume was almost equal to the number of photons. The universe cooled, the rams became non -northern and proof with anti -Barions; Their number in the unit of concomitant (expanding along with the universe) volume "frozen". But the number of photons per unit of the accompanying volume has also changed little, despite the fact that the photons were absorbed and radiated for a long time. The case is adiabatic: in the relatively slowly expanding universe, the entropy in the concomitant volume remains, and in the order of the value of the entropy is equal to the number of photons. Of course, the adiabatic and preservation of the number of photons were performed inaccurately: in the process of expanding the universe, massive particles (for example, electrons and positrons) were annihiygilated, entropy enclosed in photons, grew, but only several times, and not many orders.

All this means that only one billionaire part remained from the bariums after their annihilation with the anti -Barions, although initially the universe was almost equal to a mixture of baryons and antibarions. But the fact of the matter is that not quite equal - there were more barions for one billionth.

Actually, thanks to this one billionaire, we exist: otherwise the substance in the universe would be represented by a homogeneous extremely sparse proton-antiproton gas.

An excess of one billionth is a challenge for scientists. If the Baryons and Antibarions were exactly the same, this could be explained by the symmetry of the laws of nature (it would be no one to explain). If only the rams were originally, one could write off on the initial conditions or a certain ban principle. And one billionaire is clearly slightly disturbed symmetry. How?

Sakharov in his article was the first to adequately raised the question and gave him the right general answers that became classic. These answers, expressed in the form of necessary conditions:

1. There must be an asymmetry between the world and the anti-world, expressed in scientific language as a violation of C- and SR-symmetry.

2. The law of conservation of the bario charge must be violated (other layers

You, the number of bariums minus the number of antibarions).

3. At the initial stage of the expansion of the universe, thermodynamic balance should be impaired.

We comment on these conditions.

Condition 1. Violation of SR

Suppose the physicists of the two remote worlds in the Universe contacted each other through a certain instantaneous communication channel (as part of this mental experiment, we wave their hand to a special theory of relativity) and learned to understand each other. Some ask: what is the left thread in your documentation? Here you can’t do with a photograph, because the question will still arise, how to unfold the image - from left to right, but how to explain what is the left and right? It turns out that physicists can explain:

Take the current winding and such and such a radioactive isotope. The nuclei in the magnetic field created by the winding will be polarized. See which way to fly more electrons from beta-decay of nuclei. Direct the screwdriver in this direction and rotate it to the side where the electrons flow in your winding. In this case, the screwdriver will screw the bolt with the left thread.

Such an explanation was made because in the world at the level of the laws of physics a symmetry between the right and left. This violation is small, so for explanation it was necessary to attract rather subtle effects. Such symmetry is called p-invitations. At the same level, the symmetry between the world and the anti-world, which is called the charge, or C-invariation, is disturbed. In the anti -world, positrons will fly in the opposite direction, and the screwdriver of antiphysicians in such a setting will tighten the right bolt. Therefore, if the physicists of the two worlds doubt that they are not in anti -worlds in relation to each other, then the above instructions do not work.

Such asymmetry between the world and Antimir is quite trivial and is compensated by the replacement of the right with the left. It is clear that if the difference is only in this, then there is no skew between the barions and anti -Barions in the early universe. If the world and anti-world are the same when replacing the right with the left, this is called SR-invitations. There was a time when it was believed that the SR-invitations were performed accurately. But in the first half of the 60s, a violation of CP-symmetry was experimentally discovered. And this is a more significant difference between the world and the anti -world, although expressed very weakly.

In the light of violations of the SR-invitations, physics of different worlds can already understand whether their worlds are the same or opposite to the charge. The corresponding instruction may look as follows:

Take neutral long-lived K-Mesons. They can break up into three particles, one of which is either an electron or a positron (and the other two-charged Pi -me and antineutrino or neutrino). We, earthlings, call the positron such a particle that is more often born in these decays. If your atoms contain positrons, then you are made of antimatter. A meeting with you is contraindicated to us!

The effect that distinguishes the world from the anti -world is even weaker effect, which distinguishes the right from the left. But the initial skew between the rams is negligible - one billionth. In the mid-60s, when A.D. Sakharov worked on the article, a violation of SR-invitations has been proven. True, asymmetry between particles and antiparticles in the decays of neutral K-Mesons has not yet been discovered, a violation of SR has been manifested in a rather indirect way. However, the author refers to the so -called Okubo effect - then a theoretical conclusion that a violation of SR should lead to small charge asymmetry in the particle collapse channels - as described in the instructions. In general, by the time the article was writing for the first condition, there was a fairly solid soil underfoot. This cannot be said about the other two conditions.

Condition 2. Protone instability

If at first the number of baryons and antibarions was equal, and then there are a little more, then the baronic number is not preserved. This contradicts our experience: no one observed the breakdown of the proton, experimental restriction from below at its life time - 10,32 years, which is 22 orders of magnitude more than the life of the universe. The proton is a lightest particle carrying a bario, and it is the almost accurate preservation of the bario number that prohibits it to break up into lighter particles. On the other hand, there are no fundamental principles requiring absolutely accurate preservation of the bario (unlike an electric charge for which there is such a principle). Sakharov suggested that the proton could break up into three muons (it is three, so that the number of farms is preserved-the proton consists of three quarks). To explain the stability of protons in the current universe, he made the following assumption:

The interaction that transfers quarks into muons is carried out by a certain intermediate boson, while it is fundamentally three-part: at one point of space-time, three bosons should be used.

This requirement suppresses the breakdown of the proton today, but in the first moments of the large explosion, when the energy density and particle density are huge, the three -partial reaction was easily carried out, and the baronic number was violated strongly.

In his philosophy, the recipe was absolutely true, in a specific filling - no. With the development of the theory of elementary particles, other mechanisms were found that implements this particular scenario: a strong violation of the bario in the early universe at high density and temperature and its almost accurate preservation today. The key factor was the large mass of the intermediate boson, and not the three -patient reaction - the effect is the same, but this option fits much better into the picture, which cleared up much later. In the modern picture, the number of enzymes is not preserved, so the decay of a proton consisting of three quarks into three muons is not at all required, the proton can decay, for example, into a positron and gamma-quantum.

Condition 3. Noneal in the early universe

In the above mental experiment, we could not urge alien physicists to measure different relationships between the masses of particles or analyze atomic spectra to determine whether they live in the world or anti -world - it is most likely useless. There is a sufficiently deep principle that the masses of particles, atomic levels, and in general, are all the characteristics of phenomena, which are clearly independent of time, are the same in the world and anti -world. This principle is the name of the PRT of the theorem that claims that if Lorenz Invarianism is preserved (the principle that underlies the special theory of relativity) and the theory of particle interaction obeys a kind of simple and reasonable physical principles, then the physical world does not change when the anti-world, replacing the right with the left and turning time and time. If SR-invitations are violated, then this violation is compensated by the circulation of time.

Thus, all the values ​​characterizing stationary (non -depending on the direction of the arrows of time) processes in the world and antimire are the same, and non -stationary can be different, for example, particle breakdowns may vary.

The system that is in thermodynamic equilibrium is stationary in this sense, even if it is adiabatically slowly expanding and cooling. With adiabatic, direct and reverse reactions between particles, the decay of particles and their birth are balanced, the slow change in the system reversible and the theorem prohibiting the skew between particles and antiparticles works. In other words, with a desire for heat equilibrium, the system becomes more and more symmetrical; If processes with a violation of the baronic number are possible in it, then the bario asymmetry is washed, but not formed.

Stationarity should be violated, and this can be done, for example, the decay of very difficult particles at an early stage of expanding the universe, if the reverse reaction time is great compared to the rate of cooling.

In the mid-60s, the only particle discussed by theorists, suitable for this role, was Maximon proposed by M.A. Markov. According to the plan, he had a mass mass of particles (10-5 g), and fell out of thermodynamic equilibrium by the standards of physics almost immediately after the start of the expansion of the universe from the maximum possible (plank) temperature and density. This is what A. D. Sakharov suggested in his work.

After about 10 years, new interesting opportunities have appeared in theory for disruption - more on this below. Maximums are no longer required, there are other particles that fit well into the modern picture.

Subsequent development

The next noticeable work on the Baryon asymmetry of the Universe was the article by V.A. Kuzmina 1970. The model of interactions between elementary particles was proposed in it, in which the bario asymmetry is formed at temperatures, much lower than Plankovskaya. The mechanism remained the same - the decay of new heavy particles. But something that is not on the plank scale appears: solid soil under the feet of theorists. The fact is that at maximum temperatures and densities, the effects of quantum gravity are strong - this is that modern science is not yet tough. And at temperatures below Plankovskaya about the properties of the Universe, we can speak more or less confidently, so it became possible to connect the value of asymmetry with the parameters laid in the model and check that the observed value-one billionaire-can really be obtained.

It is remarkable that the Kuzmin model predicted a new type of processes with a violation of the bario number - transitions (oscillations) between the neutron and the antineotron. Experimenters are still looking for this process, but so far unsuccessfully.

An important stage in the development of studies on the problem of baronic asymmetry was opened by A.Yu. Ignatieva, N.V. Krasnikova, V.A. Kuzmina and A.N. Tavhelidze and the independent work of M. Yoshimura in 1978. It is associated with the construction of theories of a large association in the mid-70s, within the framework of which all known forces, with the exception of gravitational ones, have a single interaction with their origin.

True, the interactions observed now were the present only in the first moments after a large explosion at a tremendous temperature. In principle, the unification of interactions could be “felt” in our days, but it really occurs with ultra -high energies, inaccessible to either modern or future accelerators. However, in the theories of a large association, the baronic number is not automatically preserved, therefore, a strong argument in their favor would be the detection of the breakdown of the proton. The large time of the life of the proton, by the way, is precisely associated with a large scale of the energies of a large unification.

If earlier, a violation of the baronal number had to be submitted exclusively to explain the baryon asymmetry, then within the framework of the theories of a large association you can use what it is already available in them. In such a scenario, asymmetry is formed at temperatures corresponding to the kinetic energy of particles of about 1015 GEV. This is four orders of magnitude lower than the plank scale, but still a lot. Heavy particles, in the decays of which asymmetry manifests itself, there are in these theories, the sources of SR-fuel-also, therefore, it would seem, everything falls into place. Indeed, the numerous works of the late 70s and early 80s showed that it is possible to explain the observed bario asymmetry using the theories of a large unification. There are two difficulties. Firstly, it has to be assumed that the Universe was once warmed up to extremely high temperatures, and this is not very linked to the theory of the inflated universe (cosmological inflation). This theory, in which the Universe for the first moments of its existence was swollen on many orders of magnitude, naturally answers a number of difficult questions, therefore it is almost generally accepted.

Во-вторых, открытия распада протона, подтверждающего гипотезу о Большом объединении, до сих пор не произошло, несмотря на все усилия экспериментаторов.

Новый поворот произошел в 1985 г., когда В.А. Кузьмин, В.А. Рубаков и М.Е. Шапошников выяснили, что в ранней Вселенной интенсивное несохранение барионного числа происходит в результате уже известных, слабых и электромагнитных взаимодействий. При этом процессы с нарушением барионного числа идут при температурах вплоть до 100 ГэВ (в энергетических единицах), что, конечно, гораздо ниже температуры Большого объединения 1015 ГэВ. Такой результат открыл несколько новых возможностей для объяснения барионной асимметрии. Одна из них — предложенный в 1986 г. М. Фукугитой и Т. Янагидой лептогенезис — увязывает барионную асимметрию со свойствами нейтрино. Другая, пожалуй наиболее интригующая возможность — образование барион-ной асимметрии в результате фазового перехода первого рода, происходившего во Вселенной при температурах около 100 ГэВ (при сравнительно низких температурах именно в процессе фазового перехода первого рода может быть выполнено третье условие Сахарова — отклонение от теплового равновесия). Эта область энергий как раз и изучается в экспериментах на Большом адронном коллайдере, так что результаты его работы позволят выяснить, был ли такой фазовый переход. Если ответ положителен, то перспектива однозначного ответа на вопрос о происхождении асимметрии между веществом и антивеществом на основе будущих экспериментов в физике высоких энергий станет вполне реальной. Именно это направление и конкурирующий с ним лептогенезис стали современным мейнстримом в теме барионной асимметрии.

С высоты времени ряд положений статьи А.Д. Сахарова может показаться наивным. Действительно, трудно поставить себя на место человека, пытавшегося осмыслить явление раньше, чем наука дозрела до этого. Но если вдуматься, становится ясно, насколько провидческой для своего времени была данная статья.