One of the main questions that do not leave human consciousness has always been and is the question: "how did the Universe appear?" Of course, there is no unambiguous answer to this question, and it is unlikely to be obtained in the near future, but science is working in this direction and forms a certain theoretical model of the origin of our Universe. First of all, one should consider the basic properties of the Universe, which should be described within the framework of the cosmological model.
*** The model should take into account the observed distances between objects, as well as the speed and direction of their movement. Such calculations are based on Hubble's law: cz = H0D, where z is the redshift of an object, D is the distance to this object, and c is the speed of light.
*** The age of the Universe in the model must exceed the age of the oldest objects in the world.
*** The model should take into account the initial abundance of elements.
*** The model should take into account the observed large-scale structure of the Universe.
*** The model should take into account the observed background background.
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A Brief History of the Universe. Singularity as seen by the artist (photo)
Consider briefly the generally accepted theory of the origin and early evolution of the Universe, which is supported by most scientists. Today, the Big Bang theory means a combination of a model of a hot Universe with a Big Bang. And, although these concepts first existed independently of each other, as a result of their unification, it was possible to explain the initial chemical composition of the Universe, as well as the presence of relic radiation.
According to this theory, the Universe arose about 13.77 billion years ago from some dense heated object - a singular state that is difficult to describe in the framework of modern physics. The problem with the cosmological singularity, among other things, is that when describing it, most physical quantities, such as density and temperature, tend to infinity. At the same time, it is known that at an infinite density the entropy (a measure of chaos) should tend to zero, which does not coincide with an infinite temperature.
Evolution of the universe
*** The first 10 in -43 seconds after the Big Bang is called the stage of quantum chaos. The nature of the universe at this stage of existence defies description within the framework of physics known to us. There is a disintegration of a continuous single space-time into quanta.
*** Planck moment - the moment of the end of quantum chaos, which falls at 10 in -43 seconds. At this moment, the parameters of the Universe were equal to Planck values, like the Planck temperature (about 1032 K). At the time of the Planck era, all four fundamental interactions (weak, strong, electromagnetic and gravitational) were combined into one kind of interaction. It is not possible to consider the Planck moment as a certain long period, since modern physics does not work with parameters less than the Planck ones.
*** Stage of inflation. The next stage in the history of the Universe was the inflationary stage. At the first moment of inflation, the gravitational interaction separated from the unified supersymmetric field (which previously included the fields of fundamental interactions). During this period, matter has negative pressure, which causes an exponential increase in the kinetic energy of the universe. Simply put, during this period the Universe began to swell very quickly, and towards the end the energy of physical fields is converted into the energy of ordinary particles. At the end of this stage, the temperature of the substance and radiation rises significantly. Along with the end of the stage of inflation, a strong interaction stands out. Also at this moment the baryon asymmetry of the Universe arises.
[Baryon asymmetry of the Universe is the observed phenomenon of the predominance of matter over antimatter in the Universe]
*** Stage of radiation dominance. The next stage in the development of the Universe, which includes several stages. At this stage, the temperature of the Universe begins to decrease, quarks are formed, then hadrons and leptons. In the era of nucleosynthesis, the formation of initial chemical elements occurs, helium is synthesized. However, radiation still dominates over matter.
*** The era of the dominance of substance. After 10,000 years, the energy of matter gradually exceeds the energy of radiation, and their separation occurs. The substance begins to dominate the radiation, a relic background appears. Also, the separation of matter with radiation significantly increased the initial inhomogeneities in the distribution of matter, as a result of which galaxies and supergalaxies began to form. The laws of the Universe have come to the form in which we observe them today.
The above picture is composed of several fundamental theories and gives a general idea of the formation of the universe in the early stages of its existence.
Where did the universe come from?
If the universe originated from a cosmological singularity, then where did the singularity come from? It is not yet possible to give an exact answer to this question. Consider some of the cosmological models affecting the "birth of the universe".
Cyclic models. Bran modeling (photo)
These models are based on the assertion that the Universe has always existed and over time only its state changes, moving from expansion to contraction - and vice versa.
*** Steinhardt-Turok model. This model is based on string theory (M-theory), as it uses an object such as "brane".
[Bran (from the membrane) in string theory (M-theory) is a hypothetical fundamental multidimensional physical object of dimension less than the dimension of the space in which it is located]
According to this model, the visible Universe is located inside a tri-brane, which periodically, every several trillion years, collides with another tri-brane, which causes a kind of Big Bang. Further, our tri-brane begins to move away from the other and expand. At some point, the share of dark energy takes precedence and the rate of expansion of the tri-brane increases. The colossal expansion scatters matter and radiation so much that the world becomes almost homogeneous and empty. In the end, a repeated collision of tri-branes occurs, as a result of which ours returns to the initial phase of its cycle, again giving birth to our "Universe".
*** The theory of Loris Baum and Paul Frampton also says about the cyclical nature of the universe. According to their theory, the latter after the Big Bang will expand due to dark energy until it approaches the moment of the "disintegration" of space-time itself - the Big Rip. As you know, in a “closed system, entropy does not decrease” (the second law of thermodynamics). It follows from this statement that the Universe cannot return to its original state, since during such a process the entropy must decrease. However, this problem is solved within the framework of this theory. According to the theory of Baum and Frampton, an instant before the Big Rip, the Universe disintegrates into many "patches", each of which has a rather small value of entropy. Experiencing a series of phase transitions, these "scraps" of the former Universe give rise to matter and develop similarly to the original Universe. These new worlds do not interact with each other, as they scatter at a speed greater than the speed of light. Thus, scientists have avoided the cosmological singularity, with which the birth of the universe begins according to most cosmological theories. That is, at the end of its cycle, the Universe breaks up into many other non-interacting worlds that will become new universes.
*** Conformal cyclic cosmology is the cyclic model of Roger Penrose and Vahagn Gurzadyan. According to this model, the Universe is able to enter a new cycle without violating the second law of thermodynamics. This theory is based on the assumption that black holes destroy the absorbed information, which somehow "lawfully" lowers the entropy of the Universe. Then each such cycle of the existence of the Universe begins with a semblance of the Big Bang and ends with a singularity.
Other models of the origin of the universe
Among other hypotheses explaining the appearance of the visible Universe, the following two are most popular:
*** Chaotic theory of inflation - Andrey Linde's theory. According to this theory, there is a certain scalar field, which is inhomogeneous in its entire volume. That is, in different regions of the universe, the scalar field has different meanings. Then, in areas where the field is weak, nothing happens, while areas with strong fields begin to expand (inflation) due to its energy, thus forming new universes. Such a scenario implies the existence of many worlds that did not arise simultaneously and have their own set of elementary particles, and, consequently, the laws of nature.
*** The theory of Lee Smolin - assumes that the Big Bang is not the beginning of the existence of the Universe, but only a phase transition between its two states. Since before the Big Bang the universe existed in the form of a cosmological singularity, close in nature to the singularity of a black hole, Smolin suggests that the universe could have arisen from a black hole.
There are also patterns in which universes emerge continuously, branch off from their parents and find their own place. Moreover, it is not at all necessary that the same physical laws are established in such worlds. All these worlds are "nested" in a single space-time continuum, but they are so spaced apart that they do not feel each other's presence in any way. In general, the concept of inflation allows - moreover, compels! - to believe that in the gigantic megacosmos there are many isolated universes with different arrangements.
Despite the fact that cyclical and other models answer a number of questions, the answers to which cannot be given by the Big Bang theory, including the problem of the cosmological singularity. Yet, together with the inflationary theory, the Big Bang more fully explains the origin of the Universe, and also converges with many observations.
Today, researchers continue to intensively study possible scenarios for the origin of the Universe, however, to give an irrefutable answer to the question "How did the Universe appear?" - is unlikely to succeed in the near future. There are two reasons for this: direct proof of cosmological theories is practically impossible, only indirect; even theoretically, there is no way to get accurate information about the world before the Big Bang. For these two reasons, scientists can only put forward hypotheses and build cosmological models that will most accurately describe the nature of the universe we observe.