The cosmological model of the universe is a mathematical description that tries to explain the reasons for its current existence. It also depicts evolution over time.
Modern cosmological models of the Universe are based on the general theory of relativity. This is what currently provides the best view for a large-scale explanation.
The first science-based cosmological model of the universe
From his theory of general relativity, which is the hypothesis of gravity, Einstein writes equations governing the space filled with matter. But Albert thought it should be static. Thus, Einstein introduced the term, called the constant cosmological model of the Universe, into his equations in order to obtain a result.
Subsequently, taking into account the Edwin Hubble system, he will return to this idea and recognize that space can expand effectively. This is what the Universe looks like in the cosmological model of A. Einstein.
New hypotheses
Soon after, the Dutchman de Sitter, the Russian developer of the cosmological model of the Universe, Friedman and the Belgian Lemeter, presented non-static elements to the court of experts. They are necessary for solving Einstein's equations of relativity.
If de Sitter's cosmos corresponds to an empty constant, then according to the Friedmann cosmological model, the Universe depends on the density of matter inside it.
Main hypothesis
The Earth has no reason to stand in the center of space or in any privileged place.
This is the first theory of the classical cosmological model of the Universe. According to this hypothesis, the universe is considered as:
- Homogeneous, that is, it has the same properties everywhere on a cosmological scale. Of course, on a smaller plane, there are different situations if you look, for example, at the solar system or somewhere outside the galaxy.
- Isotropic, that is, always has the same properties in every direction, wherever a person looks. Moreover, the cosmos is not flattened in one direction.
The second necessary hypothesis is the universality of the laws of physics. These rules are the same anywhere and at any time.
To consider the contents of the Universe as a perfect fluid is another hypothesis. The characteristic dimensions of its components are insignificant before the distances that separate them.
Parameters
Many ask: "Describe the cosmological model of the universe." To do this, in accordance with the previous hypothesis of the Friedmann-Lemaitre system, three parameters are used that completely characterize evolution:
- Hubble constant that represents the speed of expansion.
- The mass density parameter, which measures the relationship between ρ of the Universe under study and a specific density, is called the critical ρ c associated with the Hubble constant. The current value of this parameter is marked with Ω 0 .
- The cosmological constant marked with Λ represents the force opposite to gravity.
The density of matter is a key parameter for predicting its evolution: if it is very impenetrable (Ω 0 > 1), gravity will be able to defeat expansion, and the cosmos will return to its original state.
Otherwise, the increase will continue forever. To verify this, describe the cosmological model of the universe according to theory.
Intuitively, a person can realize the evolution of the cosmos in accordance with the amount of matter inside.
A large number will lead to a closed universe. It will end in its initial state. A small amount of matter will lead to an open universe with infinite expansion. The value of Ω 0 = 1 leads to a special case of flat space.
The meaning of the critical density ρ c is about 6 x 10 –27 kg / m 3 , that is, two hydrogen atoms per cubic meter.
This very low figure explains why the modern cosmological model of the structure of the Universe suggests empty space, and it is not so bad.
Closed or open universe?
The density of matter within the universe determines its geometry.
For high impermeability, you can get a closed space with positive curvature. But with a density below critical, an open universe will come out.
It should be noted that the closed type necessarily has a finished size, while a flat or open Universe can be finite or infinite.
In the second case, the sum of the angles of the triangle is less than 180 °.
In a closed (for example, on the surface of the Earth) this figure is always greater than 180 °.
All measurements so far have not revealed the curvature of space.
Cosmological models of the universe briefly
Measurements of fossil radiation using a Boomerang ball again confirm the hypothesis of flat space.
The flat space hypothesis is in the best agreement with experimental data.
Measurements made by WMAP and Planck's satellite confirm this hypothesis.
So the universe would be flat. But this fact raises two questions for humanity. If it is flat, it means that the density of the substance is equal to the critical Ω 0 = 1. But, the largest, visible matter in the universe is only 5% of this impermeability.
As with the birth of galaxies, it is necessary to turn to dark matter again.
Age of the universe
Scientists can show that it is proportional to the inverse of the Hubble constant.
Thus, the exact definition of this constant is a critical problem for cosmology. Recent measurements show that outer space is now between 7 and 20 billion years old.
But the universe must be older than its oldest stars. And they are estimated at the age of 13 to 16 billion years.
About 14 billion years ago, the universe began to expand in all directions from an infinitely small dense point known as a feature. This event is known as the Big Bang.
During the first few seconds after the beginning of rapid inflation, which continued for the next hundreds of thousands of years, fundamental particles appeared. Which would later comprise matter, but it, as humanity knows, did not exist yet. During this period, the Universe was opaque, filled with extremely hot plasma and powerful radiation.
However, as it expanded, its temperature and density gradually decreased. Plasma and radiation were eventually replaced by hydrogen and helium, the simplest, lightest, and most common elements in the universe. Gravity took several hundred million extra years to combine these free-floating atoms into a primary gas, from which the first stars and galaxies appeared.
This explanation about the beginning of time was obtained from the standard model of the Big Bang cosmology, also known as the Lambda - Cold Dark Matter system.
Cosmological models of the Universe are based on direct observations. They are capable of making predictions that can be confirmed by subsequent studies, and rely on general relativity because this theory gives the best agreement with the observed large-scale behaviors. Cosmological models are also based on two fundamental assumptions.
The Earth is not located in the center of the Universe and does not occupy a special place, therefore the cosmos looks the same in all directions and from all places on a large scale. And the same laws of physics acting on Earth are applied throughout the cosmos regardless of time.
Therefore, what mankind observes today can be used to explain the past, present, or to help predict future events in nature, no matter how far this phenomenon is located.
It is incredible that the farther people peer into the sky, the farther they look into the past. This allows a general overview of the Galaxies when they were much younger, in order to better understand how they evolved in relation to those that are closer and, therefore, much older. Of course, humanity cannot see the same galaxies at different stages of its development. But good hypotheses may arise, grouping Galaxies into categories based on what they observe.
It is believed that the first stars formed from gas clouds shortly after the beginning of the universe. The standard big bang model suggests that you can find the earliest galaxies filled with young hot bodies that give these systems a blue tint. The model also predicts that the first stars were more numerous, but smaller in size than modern ones. And that the systems hierarchically grew to their current size, as small galaxies eventually formed large island universes.
Interestingly, many of these forecasts have been confirmed. For example, back in 1995, when the Hubble Space Telescope first looked deep into the beginning of time, he discovered that the young Universe was filled with faint blue galaxies, which were thirty to fifty times smaller than the Milky Way.
The standard big bang model also predicts that these mergers are still ongoing. Therefore, humanity must find evidence of this activity in neighboring galaxies. Unfortunately, until recently, there was little evidence of the vigor of mergers among stars near the Milky Way. This was a problem with the standard Big Bang model because it suggested that understanding the universe might be incomplete or erroneous.
Only in the second half of the 20th century, enough physical evidence was accumulated to make reasonable models of the process of space formation. The current standard Big Bang system was developed based on three basic experimental data.
Expansion of the universe
As with most models of nature, it has undergone successive improvements and created significant difficulties that fuel further research.
One of the fascinating aspects of cosmological modeling is that it reveals a series of parameter balances that must be supported fairly accurately for the universe.
Questions
The standard cosmological model of the universe is a big bang. And although the evidence supporting her is enormous, she is not without problems. The trefil in the book “Moment of Creation” shows these questions well:
- The issue of antimatter.
- The complexity of the formation of the galaxy.
- The horizon problem.
- The issue of flatness.
Antimatter Problem
After the beginning of the era of particles. There is no known process that could change the sheer number of particles in the universe. By the time space was outdated by milliseconds, the balance between matter and antimatter was fixed forever.
The main part of the standard model of matter in the Universe is the idea of pair production. This demonstrates the birth of electron-positron takes. The usual type of interaction between high life X-rays or gamma radiation and typical atoms converts most of the photon energy into an electron and its antiparticle, the positron. The masses of grains follow the Einstein relation E = mc 2 . The abyss produced has an equal number of electrons and positrons. Therefore, if all the processes of mass production were paired, in the Universe there would be exactly the same amount of matter and antimatter.
It is clear that there is some asymmetry in the way nature relates to matter. One of the promising areas of research is the violation of CP symmetry in the decay of particles by weak interaction. The main experimental evidence is the decomposition of neutral kaons. They show a slight violation of the symmetry of the SR. With the decay of kaons into electrons, humanity has a clear distinction between matter and antimatter, and this may be one of the keys to the predominance of matter in the Universe.
A new discovery at the Large Hadron Collider is the difference in the decay rate of the D-meson and its antiparticle - 0.8%, which could be another contribution to solving the issue of antimatter.
Galaxy Formation Problem
Random inhomogeneities in an expanding universe are not enough for star formation. With a fast expansion, gravitational attraction is too slow for Galaxies to form with any reasonable model of turbulence created by the expansion itself. The question of how the large-scale structure of the Universe could have arisen was the main unsolved problem in cosmology. Therefore, scientists are forced to look at a period of up to 1 millisecond to explain the existence of galaxies.
Horizon problem
Microwave background radiation from opposite directions in the sky is characterized by the same temperature within 0.01%. But the area of space from which they were emitted was 500 thousand years brighter transit time. And therefore, they could not be communicated with each other to establish a visible thermal equilibrium - they were beyond the horizon.
This situation is also called the “isotropy problem”, because the background radiation moving from all sides in space is almost isotropic. One way to express the question is to say that the temperature of parts of space in opposite directions from Earth is almost the same. But how can they be in thermal equilibrium with each other if they cannot communicate? If someone considered the return time limit of 14 billion years, obtained from the Hubble constant of 71 km / s per megaparsec, as suggested by WMAP, then he noticed that these distant parts of the Universe are located at a distance of 28 billion light years from each other. So why do they have exactly the same temperature?
In order to understand the problem of the horizon, it is enough to be twice the age of the Universe, but, as Schramm points out, if you look at this problem from earlier perspectives, it will become even more serious. At the time when the photons were actually emitted, they would be 100 times the age of the Universe or 100 times causally disabled.
This problem is one of the directions that led to the inflation hypothesis put forward by Alan Gut in the early 80s of the last century. The answer to the question of the horizon from the point of view of inflation is that at the very beginning of the Big Bang there was a period of incredibly fast inflation, which increased the size of the Universe by 10 20 or 10 30 . This means that the observable cosmos is currently inside this expansion. The radiation that can be seen is isotropic, because all this space is "inflated" from a tiny volume and has almost identical initial conditions. This is a way to explain why parts of the universe are so far away that they could never communicate with each other, look the same.
Flatness problem
The formation of the modern cosmological model of the Universe is very extensive. Observations show that the amount of matter in space is undoubtedly more than one tenth and, of course, less than the critical amount needed to stop expansion. There is a good analogy here - a ball thrown from the ground slows down. At the same speed as a small asteroid, it will never stop.
At the beginning of this theoretical throw from the system, it might seem that he was thrown at the right speed in order to move forever, decelerating to zero at an infinite distance. But over time, this has become increasingly apparent. If someone missed the speed window even by a small amount, then after 20 billion years of travel it still seemed that the ball was thrown at the right speed.
Any deviations from flatness are exaggerated over time, and at this stage of the Universe, tiny irregularities should have significantly increased. If the density of the present cosmos seems very close to critical, then it should have been even closer to flat in earlier eras. Alan Gut considers Robert Dicke's lecture to be one of the factors of influence that set him on the path of inflation. Robert pointed out that the flatness of the modern cosmological model of the Universe will require that it be flat to one part 10-14 times per second after the big bang. Kaufmann suggests that immediately after it, the density should have been equal to critical, that is, up to 50 decimal places.
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