Where did the universe come from

We publish the next fragment from Boris Stern’s book “Breakthrough over the World” - chapters from the 3rd part, which describes the theory of cosmological inflation, or the inflated universe, which answered fundamental questions, resolved paradoxes regarding the Big Bang, and finds more and more confirmations. The book was published in early June, information about it was given on the website of the Trinity Option - Science. On June 19, in the Turgenevsky library-reader (Moscow, Bobrov Lane, house 6, p. 2) at 19.00 a presentation of the book will be held, including a report of the author “One Hundred Years of Cosmology Development” and the discussion.

The details of the picture, which subsequently received the name “Cosmological inflation”, could only be collected in order to be revealed something very important that happened at the very beginning. Recall that the big explosion has long been as obvious as the sphericalness of the earth. However, the theory of the Big Bang had one very vague side: the initial conditions. They led to amazing homogeneity in causally unrelated areas, to gigantic sizes, “flat” geometry and provided enormous contents. The initial conditions were the carpet under which the main problems of cosmology had to be replaced. Moreover, it seemed that the issue of initial conditions would not be resolved in the terms of science soon, that this is rather a question for philosophers or, forgive Lord, theologians.

It turned out that this damned issue is solved by the same power of nature that gave the Earth a spherical form - gravity. Not in her gravitating hypostasis, but in the repulsive.

It was, of course, a breakthrough. Let us take the courage to call it the second cosmological revolution, which occurred in the early 1980s in several stages, which we will illuminate, adhering to chronological sequence.

Historically, the first rather worked out version of the inflation mechanism was proposed by Alexei Starobinsky in 1980. The mechanism was based on the modification of Einstein's equations-such that it affects only with a huge curvature of space-time. The modification was in addition to a member, proportional to the square of curvature of space-time. The grounds for such a modification were drawn from the quantum theory of field theory. This resembles the effect of Casimir, in which metal plates “deform” zero vibrations of the electromagnetic field in a vacuum. In the model of Starobinsky, zero fluctuations in the vacuum fields are “deformed” by a large curvature of the four-dimensional space-time. At the same time, the energy of the vacuum does not decrease, as in the effect of Casimir, but increases, and very much. This exactly corresponds to the occurrence of a scalar field, which gives gravitational molting of space. The same effect, on the other hand, is equivalent to the action of Einstein lambda-member, only in this case it is not constant, but becomes insignificant when the accelerated expansion of the universe ceased.

A retrospective analysis showed that the Starobinsky model is equivalent to a later and most realistic model of inflation with a strong field (slow rolling scenario). Unfortunately, at the time of appearance, this work did not cause proper resonance. Different reasons are called, in particular, they recall the self -isolation of Soviet science of those times. However, the article was published in a good international journal and subsequently quoted well. Moreover, in the light of new data on relict radiation, the Starobinsky model, supplemented by the work of V. Mukhanov and G. Chibisov (see below), became one of the favorites. Now, when the final data of the WMAP space microwave telescope are published and when they are analyzed along with the entire set of various data obtained by different tools, it is clear that this model fits better than many others into the overall picture.

Finally, the work of Starobinsky gained well -deserved popularity. Did Alexei himself be aware of the whole meaning of his work? Indeed, the article does not say that this mechanism allows us to solve the main problems of cosmology. However, it is better we will ask him the closest to the end of the book.

Applications that inflation decides the main paradoxes is completely clearly and with fairly persistence began to make Alan Gut, which published in the same year, but later, an article with another mechanism of cosmological inflation. It was this article that led to the emergence of a new paradigm. Perhaps not so much an article as an intensive propaganda campaign, which Gut led, speaking at dozens of conferences and seminars around the world, convincing and crushing.

Scientists are often afraid to report their results until they are published: they say, they will steal. As a rule, these are not too experienced scientists. Of course, it happens that they steal, but rarely - they do not notice or ignore much more often. Especially when the work opens the direction perpendicular to the mainstream, or is outside the scope of the main actors of this area of ​​science. In this case, stubborn advance of new results in the circle of attention of the scientific community is the same integral part of the work as writing an article. Alan Gut coped well with this part of the work.

Here is the script of Alan Guta. There is a scalar field with potential, where there is a metastable and main state. This, for example, can be an analogue of the Higgs field, but with a much higher energy density. Such a field can be responsible for violation of symmetry associated with a great association. We did not “feel” this field and will never be able to do it directly. The scalar field can be found by exciting it - by giving birth to a particle of the field, which recently happened with the Higgs field. In this case, the field particle has such a mass that you can forget about the prospects of its birth on accelerators. However, there are quite strong arguments in favor of the fact that such a field should exist. For example, the theory of a great association, in which the energy scale of this field, i.e. The characteristic potential of V 1, is well extrapolated from physics of the scale available to us: it is clear that it is only two to three orders below the plank energy.

The Guta script begins with a very dense and very hot embryo of the universe. Where did this embryo come from - a separate issue, repeatedly discussed. For example, microvo can appear as a result of a rare (but not hopelessly rare) quantum fluctuation. It is important that the embryo expands (according to the law of Friedman) and that all fields are in thermodynamic balance. The characteristic time of the first stage of the script is 10-37 or 10-36 s, during which time the embryo expanded and cooled to 1016 GEV. This is an important point, since at this temperature the density of the field of the field φ becomes comparable to the density of the energy of particles, and the effective potential of the field has a new minimum. This is the moment of the phase transition.

But the transition of the field to a new minimum is delayed - hypothermia is occurred, similar to what can happen when water freezes. The φ field “calms down”, remaining in the local minimum φ1 - precisely where the field size is zero, and the potential V 1 is huge. This metastable state is also known as a “false vacuum”. According to the witty formulation of Andrei Linde, “heavy nothing” (Heavy Nothing). As the energy of the static field cools down, the heat density of energy begins to outweigh more and more. And the pressure of a constant and homogeneous scalar field, recall, is negative. And at some point, the total pressure in the germ of the Universe changes the sign-it becomes negative. The universe is hypothermia - the scalar field gets stuck in a local minimum, in a metastable state. As it cools, the pressure goes further into the minus and finally crosses the critical line -1/3 ε.

As soon as this happens, the sign of self -tension of the universe changes. Prior to this, gravity sought to slow down the speed of expansion of the bubble, now it begins to inflate it. The size of the universe begins to grow, the curvature decreases. And the scalar field does not go anywhere-it still occupies the entire volume, only becomes more homogeneous. It turns out the same law of growth that the reproduction of neutrons with nuclear explosion or bacteria in ideal conditions has an exponential expansion. Each equal period of time type 10-37 C is doubled, and the curvature is reduced twice. And this lasts quite a long time - while the φ field remains at the minimum φ1, many dozens or hundreds of times of doubling the size of the universe can pass. During this time, from a microscopic embryo, the Universe becomes a giant, its space is completely “flat” - Euclidean.

In this case, the speed of removal of any two points from each other quickly becomes higher than the speed of light. This does not contradict anything - the points fall into the causally unrelated areas of space, no information from one point to another can be transmitted in principle. The restriction on the relative speed of the bodies in the special theory of relativity is a local principle. He is global in a stationary universe, but not in expanding. Perhaps the causal connection is not lost forever-someday, with a more slow expansion of the universe, it will recover, but at the stage of exponential inflating, any volume is quickly “scattered” into a giant number of areas who do not know anything about each other. However, it is important that these causally unrelated areas have a common origin - they remember the general conditions from which they started.

Finally, let's say after 10-35 s, the metastable field “boils”, releasing its energy into particles. How does this happen? In the script of Guta, the field in some places tunnes through a potential barrier in the main state φ0. In this case, the growing bubbles of the new phase - a true vacuum are formed. Bubbles collide, a false vacuum “fades”, transmitting its energy to the particles. The universe is warming up again, the pressure changes the sign - it becomes positive. The exponential expansion ends.

Then everything again happens according to the script of Friedman, only the universe already has giant sizes and almost zero curvature. It continues to expand with slowdown and will still grow by many orders, having experienced a number of other metamorphoses at the very beginning. At the same time, she is guaranteed almost eternal, and maybe just eternal existence.

This is the scenario of the emergence of our universe using the mechanism of cosmological inflation, which was the first to be widely known. In this scenario, however, there is one wrong episode. About him, let's say below. Very often, the achievements that changed the ideas about the world contained the wrong elements: Columbus thought that he opened the periphery of India, Copernicus considered the orbits of the planets circular, the hubble was mistaken in determining his permanent more than five times. Gut proposed a script for the birth of the Universe, which could not work in this particular form, but grabbed the essence. Therefore, before moving on to subsequent more correct scenarios, we will list the most important things recorded and clearly set out by guta in the fundamental article.

Let us return to the fundamental issues listed at the beginning of the previous part.

1. Why is the universe so great and balanced (close to "flat") with incredible accuracy? Because inflation inflated it into dozens of orders, making the curvature of the universe insignificant. Recall, according to Friedman’s equations, the dynamics of the expansion of the Universe determines the ratio of the curvature of the three -dimensional space to the constant habbla (we can compare the values ​​of different dimensions, expressing them in the plank units or, in this case, dying the curvature for the speed of light). This attitude of ωk could be a unit order before the start of inflation. In the process of inflation, the curvature decreased by many orders, and the constant Hubble has not changed. The universe has become “flat” with great accuracy - this is the “accuracy of the throw”, which provided a huge expansion time with slowdown to an insignificant speed in the remote future. If the universe is swollen, for example, 100 orders, then after inflation ωk ~ 10-100. We can speak in terms of the average density of the universe - its difference from the critical will be determined by the ωk parameter, i.e. Inflation automatically provides the most accurate balance between the expansion speed and the density - so accurate that it will remain indefinitely.
2. Why is the universe so homogeneous, although its observed areas were not causally connected in the first moments? What so agreed the parameters of a large explosion in causally unrelated areas? All the observed parts of the universe made up one causally connected region before the start of inflation. This connection was lost, but the common past, and with it the general scalar field remained. The field, practically without changing, was swollen along with space and by the end of inflation it was the same everywhere. The “burnout” of a homogeneous field gave homogeneous conditions in areas that have lost their causal connection.
3. Why in the universe there are so many particles (about 1090 only in its visible part)? In other words, where does the universe have such a large entropy? The particles formed as a result of the decay of the scalar field, which has become a lot - when the universe is expanded, the field filling it, unlike particles gas, does not change its density and remains identical to itself. That is, the total energy of the field at the inflationary stage grew exponentially. All this energy passed into particles. With the further expansion of the universe, the number of particles in the concomitant volume remained approximately the same. Moreover, there was no violation of the law of conservation of energy: at each moment, the negative gravitational energy of the universe is equal in terms of the absolute magnitude of the energy of the scalar field (and then the energy of particles). So all the contents of the huge universe were obtained as if “free”. This universe as a whole differs from any object inside it: the principle of preserving matter does not work globally - everything that is in the universe has formed from almost anything, contrary to the classics of natural science, starting with the ancient Greeks, which affirmed the impossibility of this. The immense contents of the universe in front of us. And the fact that it is obtained at the cost of an abstract negative energy of communication, does not spoil the impression of the grandiose process of creation from nothing.
4. What gave the initial impetus to the expansion of the universe? The cosmological inflation script is precisely the description of this initial push.

So far, we leave aside the fourth question: why did the physics of the universe seem to be specially fitted under the existence of man? This question will be answered below when it comes to the following stages of theory development.

Now about the incorrectness of this wonderful scenario. It consists in its final stage -in the exit from the inflation regime. Gut suggested that the field passes into a new state with zero energy through a tunnel transition at different points - the bubbles of the new phase are formed, which then grow and unite. It turns out that they are not united! In fact, the bubbles are removed from each other on continuing inflation much faster than they grow - the distance between them increases exponentially, and there is not enough birth rate of new bubbles to defeat this exponent.

If you return to the initial assumptions, then the form of potential, more precisely, the barrier between two minimums turned out to be wrong. But, as it turned out, no barrier is needed - without it everything works better and easier.

Everything is even easier

Somewhere in 1982, a conversation occurred in the dining room of Fian, which was well remembered by Igor Tkachev. The story of this conversation deserves to convey it completely.

Igor Tkachev about a long -standing conversation with Andrei Linda

At the time when the work of Guta on inflation was in hearing, Andrei spoke about some of his thoughts on this subject. It was in the Fian dining room. As I remember now, they ate borsch. In the Guta script, inflation ends when the field tunnes through a potential barrier. He believed that tunneling occurs immediately from the local minimum to the main one, as in the upper figure. To assess the probability, he used the so -called thin -walled approximation. In his script, many bubbles of the new phase formed that collided and united into a hot homogeneous universe. Andrei said that this is a big question where the field is tunnel. And if the potential is arranged so that there is no second minimum and the curve goes down at all? What then - the tunnel transition will occur to the minus infinity? No, of course! Where it goes, it must be counted, and thin -walled approximation is not suitable here. The potential after a tunnel transition cannot become higher due to the law of conservation of energy. Ниже может, но не сильно ниже — вероятность этого очень мала: под барьером наберется больший отрицательный интеграл действия, который идет в экспоненту, когда считаешь вероятность. Андрей честно посчитал, куда с наибольшей вероятностью попадает поле после туннельного перехода, причем считать пришлось на компьютере -это не так просто. Оказалось, поле туннелирует немного ниже минимума на склон, как на нижнем рисунке. И здесь, на склоне, его значение велико — не намного ниже, чем в локальном минимуме. Андрей посчитал, что происходит после этого — тут считать даже легче. Оказалось, что инфляция отнюдь не заканчивается. Поле продолжает раздувать пространство и успевает раздуть его на много порядков, пока не «сползет» вниз по склону. Из этого следовали важнейшие вещи: сценарий Гута неверен в своем конце -пузыри новой фазы, протуннелировавшие через барьер, не успевают объединиться, перемешаться и разогреться, дав однородную горячую вселенную, — они разносятся на огромные расстояния. И второе следствие: не нужно изобретать хитрые потенциалы с барьером. Инфляция может работать и без них. Это очень серьезные следствия, и Андрей, еще не очень доверяя своим результатам, стремился обсудить их с возможно большим числом коллег, заручившись поддержкой и уверенностью перед публикацией статьи.

Итак, потенциальный барьер был призван задержать скалярное поле в локальном минимуме, чтобы оно успело раздуть вселенную прежде, чем «упадет» в основное состояние. Но, оказывается, поле и без барьера может «застрять» вблизи своего первоначального значения. Для этого нужно, чтобы расширение было быстрым, а потенциал поля пологим. На языке хорошо знакомых явлений быстрое расширение играет роль вязкого трения, а наклон потенциала V (φ) аналогичен наклону поверхности, по которой катится шарик. Есть разные возможности сконструировать скалярное поле. Вариант, предложенный взамен сценария Гута Андреем Линде и на три месяца позже Андреасом Альбрехтом и Полом Стейнхардтом, — потенциал с плоской вершиной при нулевом поле и минимумом в стороне, как изображено на рис. 20.2.

Вход в стадию инфляции, как и в сценарии Гута, — термодинамический: горячая протовселенная расширяется и адиабатически охлаждается. Если в начале поле находится в термодинамическом равновесии при высокой температуре, оно должно «сесть» в нуль. Это довольно общее свойство систем — находиться при высокой температуре в наиболее симметричном состоянии (на самом деле изображенный потенциал похож на донышко бутылки в комплексных координатах, и нуль оказывается центром симметрии). При расширении зародыша вселенной опять происходит переохлаждение, и инфляция стартует точно так же, как изложено выше. И точно так же вселенная успевает раздуться на десятки порядков величины, пока поле, преодолевая вязкое трение, катится вниз с «пологой горки».

Разница в том, что в этом сценарии поле, не встречая никаких барьеров, в конце концов целиком сваливается в минимум. Потенциальная энергия поля превращается сначала в энергию его колебаний, а потом в конечном счете передается рождаемым частицам. Наступает новое термодинамическое равновесие, дальше всё идет по хорошо знакомому закону Фридмана, хотя впереди остается еще много нетривиальных событий.

Этот вариант выхода из инфляции пережил придирчивую проверку многими авторами — он действительно работает при достаточно общих предположениях.

Как в исходном сценарии Гута, так и в новом сценарии (он так и называется: «новая инфляция») остается один этап, который для своего объяснения требует слегка напрячься: как протовселенная добралась до старта инфляции? Она должна была достаточно расшириться и остыть, чтобы скалярное поле с отрицательным давлением перевесило энергию частиц и переменных полей. Дистанция от планковского состояния до начала раздувания относительно невелика, и проблема ее преодоления решается несравненно проще, чем создание огромной Вселенной без механизма инфляции. И всё же зазор в три порядка по температуре и интервал в миллион планковских времен требуется преодолеть (он именно таков, если механизм приводится в действие полем масштаба великого объединения).Вероятно, для описания этого скачка можно было бы использовать что-то вроде квантомеханического описания подбарьерного туннелирования (распад ядер и т.п.). Можно было бы… если б существовала наука под названием «квантовая гравитация». Увы, до применения квантовой механики к подобным задачам еще далеко. Но, по крайней мере, концепция туннельного перехода дает подходящую метафору (см. рис. 20.3), позволяющую легко смириться с проблемой доинфляционной стадии.

…И еще проще

Следующий важный шаг сделал Андрей Линде уже без других претендентов на приоритет. На самом деле всё может быть еще проще — инфляция может произойти без всяких хитростей типа специального потенциала с плоским максимумом в нуле и без термодинамического равновесия с переохлаждением. Возьмем произвольное поле с естественным чашеобразным потенциалом.

Предположим, что вблизи планковского состояния образовался фрагмент пространства-времени, заполненного скалярным полем. «Вблизи» означает удаление от планковских условий, достаточное для того, чтобы фрагмент мог рассматриваться в рамках классической теории. Пусть поле будет достаточно однородным, а вклад горячей материи незначительным. Тогда давление в нем может оказаться отрицательным, удовлетворяющим условию инфляции: p < -1/3 ε.

Примет ли эта инфляция «вселенский» масштаб (т.е. раздует пространство на много порядков) или тут же прекратится? Это зависит от того, насколько пологий склон потенциала и насколько быстро пошло раздувание. Напомним: скорость раздувания (постоянная Хаббла) играет роль вязкого трения. Для большой скорости раздувания требуется большое отрицательное давление, значит, и большая плотность энергии, она же — потенциал поля ( V (φ) на картинке и ε в формуле совпадают, если поле однородно и постоянно). А для пологости склона ось Х должна быть длинной, т.е. величина φ должна быть большой. Величина поля имеет размерность массы,и необходимое значение оказывается больше планковской массы. Ничего страшного, величина поля — достаточно абстрактная величина, главное, чтобы значение потенциала было ниже планковского масштаба — тогда есть классическое пространство-время, с которым можно работать. Еще важно, чтобы поле было достаточно однородным в некоторой области пространства, в несколько раз превышающей размеры горизонта.

Так вот, если «чаша» потенциала достаточно широка и если природа пробует любые стартовые условия, то она обязательно попробует и те, что перечислены выше. И тут уже возврата нет — готова гигантская вселенная. And not only. Но об этом «не только» — ниже.

Из-за того, что для запуска механизма достаточно подходящей комбинации из разнообразного множества случайных начальных условий, Андрей Линде назвал этот сценарий хаотической инфляцией. Только надо помнить, что термин «хаотический» относится лишь к старту. В дальнейшем всё происходит, как и в предыдущем варианте, — вполне регулярно и с предсказуемым исходом.

Большое преимущество этого сценария в том, что не требуется ни термодинамического равновесия, ни фазового перехода, предшествующих инфляции. В сценариях Гута и «новой инфляции» цепочка событий выглядела следующим образом: горячая вселенная — переохлаждение — инфляция — горячая вселенная. В случае с хаотической инфляцией первые две стадии, каковые, безусловно, являются обузой, отпадают. Не надо больше объяснять, как установилось доинфляционное термодинамическое равновесие (далеко не очевидно, что это возможно), не нужен весьма специфический вид потенциала и т.п.

Пожалуй, хаотическая инфляция и есть общепринятая ныне концепция зарождения Вселенной, точнее, ее часть.