The cosmological model of the Universe is a mathematical description that attempts 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 representation for a large-scale explanation.
The first science-based cosmological model of the Universe
From his theory of general relativity, which is a hypothesis of gravity, Einstein writes equations that govern a cosmos filled with matter. But Albert thought it should be static. So Einstein introduced a term called the constant cosmological model of the universe into his equations to get the result.
Subsequently, given the system of Edwin Hubble, he will return to this idea and recognize that the cosmos can effectively expand. Exactlythe Universe looks like in A. Einstein's cosmological model.
New hypotheses
Shortly after him, the Dutchman de Sitter, the Russian developer of the cosmological model of the Universe Friedman and the Belgian Lemaitre present non-static elements to the judgment of connoisseurs. They are needed to solve Einstein's equations of relativity.
If the de Sitter 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
There is no reason for the Earth to stand in the center of space or in any privileged location.
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 scale, there are different situations if you look, for example, at the Solar System or somewhere outside the Galaxy.
- Isotropic, that is, it always has the same properties in every direction, no matter where a person looks. Especially since space is not flattened in one direction.
The second necessary hypothesis is the universality of the laws of physics. These rules are the same everywhere and at all times.
Considering the content of the universe as a perfect fluid is another hypothesis. The characteristic dimensions of its components are insignificant compared to the distances that separate them.
Parameters
Many ask: "Describe the cosmological modelUniverse." To do this, in accordance with the previous hypothesis of the Friedmann-Lemaitre system, three parameters are used that fully characterize evolution:
- Hubble constant that represents the rate of expansion.
- The mass density parameter, which measures the ratio between the ρ of the investigated Universe and a certain density, is called the critical ρc, which is related to the Hubble constant. The current value of this parameter is marked Ω0.
- The cosmological constant, marked Λ, is the opposite force to gravity.
The density of matter is a key parameter for predicting its evolution: if it is very impenetrable (Ω0> 1), gravity will be able to defeat the expansion and the cosmos will return to its original state.
Otherwise the increase will continue forever. To check this, describe the cosmological model of the Universe according to the theory.
It is intuitively clear that 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 Ω0=1 leads to a special case of flat space.
The meaning of the critical density ρc is about 6 x 10–27 kg/m3, that is, two hydrogen atoms per cubic meter.
This very low figure explains why modernthe cosmological model of the structure of the universe assumes empty space, and this is not so bad.
Closed or open universe?
The density of matter inside the universe determines its geometry.
For high impermeability, you can get a closed space with positive curvature. But with a density below the critical one, an open universe will emerge.
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 failed to reveal the curvature of space.
Cosmological models of the Universe briefly
Measurements of fossil radiation using the Boomerang ball again confirm the flat space hypothesis.
The flat space hypothesis is in best agreement with experimental data.
Measurements made by WMAP and the Planck satellite confirm this hypothesis.
So the universe would be flat. But this fact puts humanity before two questions. If it is flat, it means that the substance density is equal to the critical one Ω0=1. But, the largest, visible matter in the universe is only 5% of this impenetrability.
Just as with the birth of galaxies, it is necessary to turn again to dark matter.
Age of the Universe
Scientists canshow that it is proportional to the reciprocal of the Hubble constant.
Thus, the exact definition of this constant is a critical problem for cosmology. Recent measurements show that the cosmos is now between 7 and 20 billion years old.
But the universe must necessarily be older than its oldest stars. And they are estimated to be between 13 and 16 billion years old.
About 14 billion years ago, the universe began to expand in all directions from an infinitely small dense point known as a singularity. This event is known as the Big Bang.
Within the first few seconds of the onset of rapid inflation, which continued for the next hundreds of thousands of years, fundamental particles appeared. Which would later make up matter, but, as humanity knows, it did not yet exist. 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 eventually replaced hydrogen and helium, the simplest, lightest, and most abundant elements in the universe. Gravity took several hundred million extra years to combine these free-floating atoms into the primordial gas from which the first stars and galaxies emerged.
This explanation of the beginning of time was derived from the standard model of Big Bang cosmology, also known as the Lambda system - cold dark matter.
Cosmological models of the Universe are based on direct observations. They are capable of doingpredictions that can be confirmed by subsequent studies and rely on general relativity because this theory gives the best fit with observed large-scale behaviors. Cosmological models are also based on two fundamental assumptions.
Earth is not located in the center of the universe and does not occupy a special place, so space looks the same in all directions and from all places on a large scale. And the same laws of physics that apply on Earth apply throughout the cosmos regardless of time.
Hence, what humanity observes today can be used to explain the past, the present, or to help predict future events in nature, no matter how far away the phenomenon is.
Unbelievable, the further people look into the sky, the further they look into the past. This allows a general overview of the Galaxies when they were much younger, so that we can 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 can arise, grouping the Galaxies into categories based on what they observe.
The first stars are believed to have formed from gas clouds shortly after the beginning of the universe. The Standard Big Bang Model suggests that it is possible to find the earliest galaxies filled with young hot bodies that give these systems a blue tint. The model also predicts thatthe first stars were more numerous, but smaller 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 predictions have been confirmed. For example, back in 1995, when the Hubble Space Telescope first looked deep into the beginning of time, it discovered that the young universe was filled with faint blue galaxies 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 has been little evidence of energetic mergers among stars near the Milky Way. This was a problem with the standard big bang model because it suggested that the understanding of the universe could be incomplete or wrong.
Only in the second half of the 20th century was enough physical evidence accumulated to make reasonable models of how the cosmos formed. The current standard big bang system was developed from three main experimental data.
Expansion of the Universe
As with most models of nature, it has undergone successive improvements and has created significant challenges that fuel further research.
One of the fascinating aspects of the cosmologicalmodeling is that it reveals a number of balances of parameters that must be maintained accurately enough for the universe.
Questions
The standard cosmological model of the universe is a big bang. And while the evidence supporting her is overwhelming, she's not without problems. Trefil in the book "The Moment of Creation" shows these questions well:
- The problem of antimatter.
- The complexity of the formation of the Galaxy.
- Horizon problem.
- A question of flatness.
The Antimatter Problem
After the start of the particle era. There is no known process that could change the sheer number of particles in the universe. By the time space was milliseconds out of date, 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 doubles. The usual type of interaction between high life x-rays or gamma rays and typical atoms converts most of the photon's energy into an electron and its antiparticle, the positron. The particle masses follow Einstein's relation E=mc2. The produced abyss has an equal number of electrons and positrons. Therefore, if all mass production processes were paired, there would be exactly the same amount of matter and antimatter in the Universe.
It is clear that there is some asymmetry in the way nature relates to matter. One of the promising areas of researchis the violation of CP symmetry in the decay of particles by the weak interaction. The main experimental proof is the decomposition of neutral kaons. They show a slight violation of the SR symmetry. 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.
New discovery at the Large Hadron Collider - the difference in the decay rate of the D-meson and its antiparticle is 0.8%, which can be another contribution to solving the issue of antimatter.
The Galaxy Formation Problem
Random irregularities in the expanding universe are not enough to form stars. In the presence of rapid expansion, the gravitational pull is too slow for galaxies to form with any reasonable pattern of turbulence created by the expansion itself. The question of how the large-scale structure of the universe could have arisen has been a major 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 radiated was 500 thousand years lighter transit time. And so they could not communicate with each other to establish apparent thermal equilibrium - they were outsidehorizon.
This situation is also called the "isotropy problem" because the background radiation moving from all directions in space is almost isotropic. One way to put the question is to say that the temperature of parts of space in opposite directions from the Earth is almost the same. But how can they be in thermal equilibrium with each other if they can't communicate? If one considered the return time limit of 14 billion years, derived from the Hubble constant of 71 km/s per megaparsec, as proposed by WMAP, one noticed that these distant parts of the universe are 28 billion light years apart. So why do they have exactly the same temperature?
You only need to be twice the age of the universe to understand the horizon problem, but as Schramm points out, if you look at the problem from an earlier perspective, it becomes even more serious. At the time the photons were actually emitted, they would have been 100 times the age of the universe, or 100 times causally disabled.
This problem is one of the directions that led to the inflationary hypothesis put forward by Alan Guth in the early 1980s. The answer to the horizon question in terms of inflation is that at the very beginning of the Big Bang process there was a period of incredibly rapid inflation that increased the size of the universe by 1020 or 1030 . This means that the observable space is currently inside this extension. 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 of explaining why parts of the universe are so far away that they could never communicate with each other, look the same.
The problem of flatness
The formation of the modern cosmological model of the Universe is very extensive. Observations show that the amount of matter in space is certainly more than one-tenth and certainly less than the critical amount needed to stop expansion. There is a good analogy here - a ball thrown from the ground slows down. With the same speed as a small asteroid, it will never stop.
At the start of this theoretical throw from the system, it might appear that it was thrown at the right speed to go forever, slowing down to zero over an infinite distance. But over time it became more and more obvious. If anyone missed the window of speeds even by a small amount, after 20 billion years of travel, it still seemed like the ball was thrown at the right speed.
Any deviations from flatness are exaggerated over time, and at this stage of the universe, the tiny irregularities should have increased significantly. If the density of the current cosmos seems very close to critical, then it must have been even closer to flat in earlier eras. Alan Guth credits Robert Dicke's lecture as one of the influences that put him on the path of inflation. Robert pointed out thatthe flatness of the current cosmological model of the universe would require it to be flat to one part in 10–14 times per second after the big bang. Kaufmann suggests that immediately after it, the density should have been equal to the critical one, that is, up to 50 decimal places.
In the early 1980s, Alan Guth suggested that after the Planck time of 10–43 seconds, there was a brief period of extremely rapid expansion. This inflationary model was a way of dealing with both the flatness problem and the horizon issue. If the universe swelled up by 20 to 30 orders of magnitude, then the properties of an extremely small volume, which could be considered tightly bound, were propagated throughout the known universe today, contributing to both extreme flatness and an extremely isotropic nature.
This is how the modern cosmological models of the Universe can be briefly described.
