Such statements are akin to those great ideas that radically change the view of our place in this world. One of these revolutions in consciousness occurred in 1543, when Nicolaus Copernicus showed that the Earth is not the center of the Universe. In the 20s of the 20th century, Edwin Hubble, noticing that galaxies in the Universe were moving away from each other, gave birth to the idea that our Universe did not exist forever, but was formed as a result of a certain event - the Big Bang. Now we are on the verge of a new discovery. If the limits of the Universe are found, we will be faced with a new, even more difficult question: what is there on the other side of the boundaries?

Let's navigate by the stars

The infinity of the Universe implies that it must be infinite not only in space, but also in time, and therefore have an infinite number of stars. In this case, our sky would be completely dotted with luminaries and dazzlingly bright around the clock. However, the darkness of the sky indicates that the cosmos did not exist forever. According to the popular theory, it all began with the Big Bang, which gave rise to the very existence and expansion of matter. This concept itself refutes the idea of ​​the eternity of the Universe, and therefore undermines the belief in its infinity. At the same time, the Big Bang theory creates certain difficulties for astronomers searching for the boundaries of our outer space.

“The fact is that traveling over vast distances takes light years, and, therefore, scientists always receive outdated data. The space traversed by light in the early Universe grew due to its subsequent expansion. The stars closest to us are relatively young; distant objects are already thousands of years old, and if you look at other galaxies, then billions. However, we do not see all galaxies. 13.7 billion years is the maximum available to us,” explains Neil Cornish, an astrophysicist from the Montana State University. A kind of barrier to our vision is the relict radiation, formed approximately 380 thousand years after the Big Bang, when the Universe expanded and cooled so much that atoms appeared. This radiation is something like a child's photograph of space, in which it is captured even before the stars appeared. Behind it there can exist both boundaries and an endlessly continuing Universe. But, despite the power of telescopes, this area remains invisible.

Space music

CMB prevents scientists from peering into the farthest reaches of space, but at the same time it carries very valuable information contained in the microwave background. Scientists suggest that if the Universe were of unlimited size, waves of all possible lengths could be found in it. However, in fact, the wave spectrum of space is very narrow: truly large waves NASA's WMAP apparatus, designed to study cosmic microwave background radiation, has never detected it. "The universe has properties musical instrument, inside which the wavelength cannot exceed its length. We realized that the Universe does not vibrate at long wavelengths, which confirmed its finitude,” says Jean Pierre Luminet from the Paris Observatory in France.

The only thing left to do is to determine its boundaries and shape. Glen Starkmann, a physicist from Canada working at Cleveland's Case Western University, believes he has found a way to determine the boundaries of the Universe, even if they are further than our line of sight. This can be done again using waves. “The sound waves that spread throughout the Universe during its youth can tell a lot. The shape of the universe, like the shape of a drum, determines what type of vibrations will occur in it,” says Glen. His team plans to use spectral analysis to our Universe in order to determine its shape based on the sounds it makes. True, these studies are long-term, and it may take years to find an answer.

We live in a donut...

However, there is another way to find out whether the Universe has boundaries. This is what Zhanna Levin, a theorist from Cambridge University, is currently doing. She explains the principle of building the Universe using the example of the good old computer game"Asteroids". If a player-controlled spaceship goes up, off the screen, it will immediately appear below. Such a strange maneuver becomes understandable if you mentally roll the screen into a tube, like a magazine: it turns out that the device is simply moving in a circle.
“In the same way, we, living inside the Universe, cannot get out. We do not have access to a dimension from which we could look at our three-dimensional Universe from the outside. Take, for example, a bagel - this, by the way, is quite suitable for in this case form for the Universe - although its surface is clearly defined, none of those living inside will stumble upon its limits: it seems to them that no boundaries exist,” says Zhanna.

However, there is still a chance to recognize these limits, albeit scanty - you need to monitor how the light behaves. Let's imagine that the Universe is a room, and you, armed with a flashlight, stand in its center. The light from the flashlight will reach the wall behind you and then reflect off the wall opposite. and you will see the reflection of your own back in it. The same rules can work in limited space. "Light portraits" can be reflected from supposed space walls and thus duplicated many times, but with some changes. And be the Universe a little more than Earth, the light would instantly circle around it, and distorted images of the planet would appear throughout the sky. But space is so vast that light will take billions of years to travel around it and be reflected.

But let's return to our “steering wheels”. Zhanna Levin, with her theory of the donut-shaped Universe, found support in the person of Frank Steiner from the University of Ulm in Germany. After analyzing the data obtained using WMAP, this scientist concluded that the Donut Universe provides the greatest agreement with the observed cosmic microwave background radiation. His team also tried to guess the likely size of the Universe - according to research, it could reach 56 billion light years across.

...or in a soccer ball?

Jean Pierre Luminet, with all his respect for Ms. Levine's donut, is still confident that the Universe is a spherical dodecahedron or, more simply, a soccer ball: twelve pentagonal rounded surfaces arranged symmetrically. In fact, the theory of the French scientist does not particularly contradict the scientific research of Zhanna Levin with her game of “Asteroids”. The same scheme works here - leaving one of the sides, you find yourself on the opposite. For example, if you fly in a straight line on some “high-speed” rocket, you can eventually return to the starting point. Jean-Pierre does not deny the principle of mirror reflections. He is sure that if a super-powerful telescope existed, it would be possible to see different sides space the same objects, only on different stages life. But when the edges of the dodecahedron are billions of light years away, faint reflections on them cannot be noticed even by the most observant astronomers.

It should be noted that Lumine, with his concept of a soccer ball, found an ally - mathematician Jeffrey Weeks. This scientist claims that the waves in the cosmic microwave background look exactly the same as they would look if they originated inside a regular geometric figure with twelve pentagonal faces.

Inflation on a universal scale

The first moment of the life of the Universe played huge role in its further evolution. Scientists are still building complex hypotheses about inflation - a very short period of time, much less than a second, during which the size of the Universe increased a hundred trillion times. Most scientists are inclined to believe that the expansion of the Universe is still continuing. And it would seem that the theory of the infinity of space is a logical continuation of the idea of ​​inflation.

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Computer model of the Universe

However, Andy Albracht, a theoretical physicist at the University of California, Davis, has a different opinion on this matter: although the expansion of the Universe continues to this day, this process still has limits. To explain his theory, Andy chose a metaphor for the universe soap bubble. Traditional inflation theory allows for an infinite expansion of this bubble, but even kindergarteners know that sooner or later the bubble must burst. Andy believes that, having reached its maximum, inflation should stop. And this maximum is not as great as we think. According to Olbracht, the Universe is only 20% larger than the space we see. “Of course, it is incredibly difficult to come from infinity to such a tiny size - only some 20% larger! I even started to feel claustrophobic,” the scientist jokes. Of course, Olbracht's conclusions are very controversial and require factual confirmation, but for now most astronomers believe that inflation will not die out very soon.

Dark Stream and Other Universes

The expansion of the Universe, by the way, is the best explanation for the movement of galaxies in the territory visible to us. True, some features of this galactic movement are puzzling. A group of NASA specialists led by astrophysicist Alexander Kashlinsky, studying microwave and X-ray radiation, discovered that about eight hundred distant galaxy clusters are moving together in one direction at a speed of a thousand kilometers per second, as if they are attracted by some kind of magnet. This universal movement was called the "dark flow." According to the latest data, it already covers 1400 galaxies. They are heading towards an area located more than three billion light years from Earth. Scientists suggest that just somewhere there, beyond the limits of observation, there is a huge mass that attracts matter. However, according to the existing theory, the matter after the Big Bang, which gave birth to our Universe, was distributed more or less evenly, which means that there cannot be concentrations of masses with such fantastic power. Then what's there?

The answer to this question was given by theoretical physicist Laura Mersini-Hoftan, leader of the group from the University of North Carolina. She seriously considers the existence of another Universe located next to ours. Her conclusions, which seem incredible at first glance, are quite compatible with the theory of inflation and the “soap bubble” voiced by Andy Albracht, as well as with the “dark flow” of Alexander Kashlinsky. Now the research of these scientists will form a single picture like a puzzle. The dark flow observed in our outer space may be triggered by one of the neighboring “bubbles” - another Universe.

Hoftan explains the multiplicity of universes using the theory of probability. She considers the birth of our world a miracle; it could easily not have appeared: the chances of its occurrence are negligible and amount to 1 in 10133.

“We can ask the question about the origin of the Universe when we have a multiple structure in which it was formed - places in which conditions are favorable for its origin. In other words, we can imagine many Big Bangs and many universes,” notes Hoftan. For clarity, she compares these favorable places to hotel rooms. The universe can only originate in a free “room” and exist there alone. However, this does not mean that another such cosmoworld cannot move into the “room” through the wall. But if our Universe is a hotel room, should we be able to hear our neighbors? In 2007, the WMAP apparatus recorded an unusual region of significantly reduced background radiation, which indicates the absence of matter in it. According to the scientist, the only explanation for such a cold and absolute void is that some other forces are at work there, perhaps the presence of another Universe, the huge mass of which attracts neighboring matter. And although these “alien” objects are beyond our sight, our neighbor still makes itself felt with messages in the form of a cold spot and a stream of galactic clusters.

Of course, the scientific community has had mixed reactions to the findings about multiple universes. However, scientists trying to characterize outer space, are ready to accomplish new revolutions in science. Our Universe, previously considered infinite, may cease to be so and take its rightful place in space, among such a number of universes that it is impossible to even imagine.

The next version of the structure of the Universe was put forward by physicist Frank Steiner from the University of Ulm, who, together with his colleagues, re-analyzed the data collected by the Wilkinson Microwave Anisotropy Probe (WMAP) space probe, which was once launched for detailed photography of the cosmic microwave background radiation.

However, do not rush to talk about the edges of the Universe. The fact is that this polyhedron is closed on itself, that is, having reached one of its faces, you will simply get back inside through the opposite side this multidimensional “Möbius loop”.

Interesting conclusions follow from this presentation. For example, that by flying on some “high-speed” rocket in a straight line, you can eventually return to the starting point, or, if you take a “very large” telescope, you can see the same objects in different directions of space, only due to finitude speed of light - at different stages of life.

Scientists have tried to make such observations, but nothing like “ specular reflections» was not found. Either because the model is incorrect, or because the “range” of modern observational astronomy is not enough. Nevertheless, the discussion about the shape and size of the Universe continues.

Now Steiner and his comrades have added new wood to the fire.

Planck weighs about two tons. It should cruise around the Lagrange point L2. As the satellite rotates around its axis, it will gradually capture a complete map of the microwave background with unprecedented accuracy and sensitivity (illustrations by ESA/AOES Medialab and ESA/C. Carreau).

The German physicist compiled several models of the Universe and checked how microwave background density waves are formed in them. He claims that the closest match to the observed cosmic microwave background radiation is provided by the donut universe, and even calculated its diameter. The “donut” turned out to be 56 billion light years across.

True, this torus is not quite ordinary. Scientists call it a 3-torus. Its actual form is difficult to imagine, but researchers explain how to at least try.

First, imagine how a regular “donut” is formed. You take a piece of paper and roll it into a tube, gluing two opposite edges together. Then you roll the tube into a torus, gluing its two opposite “exits” together.

With a 3-torus, everything is the same, except that the starting ingredient is not a sheet, but a cube, and you need to glue not the edges of the planes, but each pair of opposite faces. Moreover, glue it in such a way that, having left the cube through one of its faces, you will find that you again got inside through its opposite face.

Several experts who commented on Steiner's work noted that it does not definitively prove that the Universe is a “multidimensional donut”, but only that this shape is one of the most likely. Also, some scientists add that the dodecahedron (which is often compared to soccer ball, although this is incorrect) is still a “good candidate”.

Frank's answer to this is simple: the final choice between forms can be made after more accurate measurements of the cosmic microwave background radiation than those carried out by WMAP. And such a survey will soon be carried out by the European satellite Planck, which is scheduled to launch on October 31, 2008.

“From a philosophical point of view, I like the idea that the Universe is finite and one day we might be able to fully explore it and know everything about it. But since questions in physics cannot be solved by philosophy, I hope that Planck will answer them,” says Steiner.

Don't try to erase the past. It shapes you today and helps you become who you will be tomorrow.

Ziad K. Abdelnoir

The universe, even more than you and me, is shaped by the conditions that existed at the time of its birth. But what form did it take? I chose a question from reader Tom Berry who asks:

I understand that the universe has the shape of a saddle. I wonder why, at the moment of the Big Bang, all matter did not scatter evenly in all directions and give the universe a spherical shape?

Let's start by removing one dimension and talking about what makes up a two-dimensional surface. You will probably imagine a plane - like a sheet of paper. It can be rolled into a cylinder, and although the surface will be self-connected - you can go from one side to the other, it will still be a flat surface.

What does it mean? For example, you can draw a triangle and add up the dimensions internal corners. If we get 180 degrees, then the surface is flat. If you draw two parallel lines, they will remain that way throughout.

But this is just one of the options.

The surface of a sphere is two-dimensional, but not flat. Any line begins to curve, and if you add the angles of a triangle, you will get a value greater than 180 degrees. By drawing parallel lines (lines that start out as parallel), you will see that they will eventually meet and intersect. Such surfaces have positive curvature.

The seat surface, on the other hand, represents another type of non-planar two-dimensional surface. It is concave in one direction and convex in the other, perpendicular, and is a surface with negative curvature. If you draw a triangle on it, you will get the sum of the angles less than 180 degrees. Two parallel lines will diverge in different directions.

You can also imagine a flat round piece of paper. If you cut a wedge out of it and glue it back together, you get a surface of positive curvature. If you insert this wedge into another similar piece, you will get a surface of negative curvature, as in the picture.

It is quite easy to represent a two-dimensional surface from three-dimensional space. But in our three-dimensional Universe, everything is somewhat more complicated.

As for the curvature of the Universe, we have three options:

Positive curvature, like a sphere in higher dimensions
- negative, like a saddle in higher dimensions
- zero (flat) – like a three-dimensional lattice

One might think that the presence of the Big Bang implies the first, spherical option, since the Universe seems to be the same in all directions - but this is not so. There are very interesting reason, according to which the Universe is the same in all directions - and it has nothing to do with curvature.

The fact that the Universe is the same in all places (homogeneous) and directions (isotropic) proves the existence of the Big Bang, the hypothesis of which says that everything began with a hot and dense homogeneous state in which the initial conditions and laws of nature were the same everywhere.

Over time, small deviations lead to the appearance of structures - stars, galaxies, clusters, and great voids. But the reason for the homogeneity of the universe is that everything had the same beginning, and not because of curvature.

But we can measure the amount of curvature.

The picture shows fluctuation patterns captured in background cosmic radiation. How the Universe works and what it is made of determines the peaks of fluctuations - the hottest and coldest places at specific angular scales. If the Universe has a negative curvature (saddle), the Universe tends to a smaller scale, if it has a positive curvature, it tends to a larger scale.

The reason is the same as we described - how straight lines behave on these surfaces.

So we just need to study the fluctuations in the background cosmic microwave radiation, and we can measure the curvature of the observable Universe.

So what do we get?

And we find that the amount of curvature shown in the blue circles is approximately 0.5%. This suggests that the curvature of the Universe is indistinguishable from plane.

It really expanded evenly in all directions, but this has nothing to do with curvature. Of course, on much larger scales than we can observe, the curvature of the Universe may be non-zero. The inflationary process that occurred after the Big Bang exponentially enlarges every part of the Universe.

That is, it is possible that the curvature of the Universe is positive or negative, that it is like a saddle or a sphere, that it can be self-connected, and we can exit from one end and get to the other. This cannot be ruled out - but in the observed part this is not the case. And for us the Universe is indistinguishable from being flat. But, as shown in the figure in Part D, you can assume that your space is flat, but the Universe may not be flat. This is a conclusion from the information we have.

Did you know that the Universe we observe has fairly definite boundaries? We are used to associating the Universe with something infinite and incomprehensible. However modern science to the question about the “infinity” of the Universe offers a completely different answer to such an “obvious” question.

According to modern ideas, the size of the observable universe is approximately 45.7 billion light years (or 14.6 gigaparsecs). But what do these numbers mean?

The first question that comes to mind to an ordinary person– how can the Universe not be infinite? It would seem that it is indisputable that the container of all that exists around us should have no boundaries. If these boundaries exist, what exactly are they?

Let's say some astronaut reaches the boundaries of the Universe. What will he see in front of him? A solid wall? Fire barrier? And what is behind it - emptiness? Another Universe? But can emptiness or another Universe mean that we are on the border of the universe? After all, this does not mean that there is “nothing” there. Emptiness and another Universe are also “something”. But the Universe is something that contains absolutely everything “something”.

We arrive at an absolute contradiction. It turns out that the boundary of the Universe must hide from us something that should not exist. Or the boundary of the Universe should fence off “everything” from “something”, but this “something” should also be part of “everything”. In general, complete absurdity. Then how can scientists declare the limiting size, mass and even age of our Universe? These values, although unimaginably large, are still finite. Does science argue with the obvious? To understand this, let's first trace how people came to our modern understanding of the Universe.

Expanding the boundaries

Since time immemorial, people have been interested in what the world around them is like. There is no need to give examples of the three pillars and other attempts of the ancients to explain the universe. As a rule, in the end it all came down to the fact that the basis of all things is the earth's surface. Even in the times of antiquity and the Middle Ages, when astronomers had extensive knowledge of the laws of planetary movement along the “fixed” celestial sphere, the Earth remained the center of the Universe.

Naturally, back in Ancient Greece there were those who believed that the Earth revolves around the Sun. There were those who spoke about the many worlds and the infinity of the Universe. But constructive justifications for these theories arose only at the turn of the scientific revolution.

In the 16th century, Polish astronomer Nicolaus Copernicus made the first major breakthrough in knowledge of the Universe. He firmly proved that the Earth is only one of the planets revolving around the Sun. Such a system greatly simplified the explanation of such a complex and intricate movement of planets in the celestial sphere. In the case of a stationary Earth, astronomers had to come up with all sorts of clever theories to explain this behavior of the planets. On the other hand, if the Earth is accepted as moving, then an explanation for such intricate movements comes naturally. Thus, a new paradigm called “heliocentrism” took hold in astronomy.

Many Suns

However, even after this, astronomers continued to limit the Universe to the “sphere of fixed stars.” Until the 19th century, they were unable to estimate the distance to the stars. For several centuries, astronomers have tried to no avail to detect deviations in the position of stars relative to the Earth’s orbital movement (annual parallaxes). The instruments of those times did not allow such precise measurements.

Finally, in 1837, the Russian-German astronomer Vasily Struve measured parallax. This marked a new step in understanding the scale of space. Now scientists could safely say that the stars are distant similarities to the Sun. And our luminary is no longer the center of everything, but an equal “resident” of an endless star cluster.

Astronomers have come even closer to understanding the scale of the Universe, because the distances to the stars turned out to be truly monstrous. Even the size of the planets’ orbits seemed insignificant in comparison. Next it was necessary to understand how the stars are concentrated in .

Many Milky Ways

The famous philosopher Immanuel Kant anticipated the foundations of the modern understanding of the large-scale structure of the Universe back in 1755. He hypothesized that the Milky Way is a huge rotating star cluster. In turn, many of the observed nebulae are also more distant “milky ways” - galaxies. Despite this, until the 20th century, astronomers believed that all nebulae are sources of star formation and are part of the Milky Way.

The situation changed when astronomers learned to measure distances between galaxies using . The absolute luminosity of stars of this type strictly depends on the period of their variability. By comparing their absolute luminosity with the visible one, it is possible to determine the distance to them with high accuracy. This method was developed in the early 20th century by Einar Hertzschrung and Harlow Scelpi. Thanks to him, the Soviet astronomer Ernst Epic in 1922 determined the distance to Andromeda, which turned out to be an order of magnitude larger size Milky Way.

Edwin Hubble continued Epic's initiative. By measuring the brightness of Cepheids in other galaxies, he measured their distance and compared it with the redshift in their spectra. So in 1929 he developed his famous law. His work definitively disproved the established view that the Milky Way is the edge of the Universe. Now he was one of the many galaxies that had once considered him integral part. Kant's hypothesis was confirmed almost two centuries after its development.

Subsequently, the connection discovered by Hubble between the distance of a galaxy from an observer relative to the speed of its removal from him, made it possible to draw a complete picture of the large-scale structure of the Universe. It turned out that the galaxies were only an insignificant part of it. They connected into clusters, clusters into superclusters. In turn, superclusters form the largest known structures in the Universe—threads and walls. These structures, adjacent to huge supervoids (), constitute a large-scale structure known in at the moment, Universe.

Apparent infinity

It follows from the above that in just a few centuries, science has gradually fluttered from geocentrism to a modern understanding of the Universe. However, this does not answer why we limit the Universe today. After all, until now we were talking only about the scale of space, and not about its very nature.

The first who decided to justify the infinity of the Universe was Isaac Newton. Having discovered the law of universal gravitation, he believed that if space were finite, all its bodies would sooner or later merge into a single whole. Before him, if anyone expressed the idea of ​​​​the infinity of the Universe, it was exclusively in a philosophical vein. Without any scientific basis. An example of this is Giordano Bruno. By the way, like Kant, he was many centuries ahead of science. He was the first to declare that stars are distant suns, and planets also revolve around them.

It would seem that the very fact of infinity is quite justified and obvious, but the turning points of science of the 20th century shook this “truth”.

Stationary Universe

The first significant step towards developing a modern model of the Universe was taken by Albert Einstein. The famous physicist introduced his model of a stationary Universe in 1917. This model was based on the general theory of relativity, which he had developed a year earlier. According to his model, the Universe is infinite in time and finite in space. But, as noted earlier, according to Newton, a Universe with a finite size must collapse. To do this, Einstein introduced a cosmological constant, which compensated for the gravitational attraction of distant objects.

No matter how paradoxical it may sound, Einstein did not limit the very finitude of the Universe. In his opinion, the Universe is a closed shell of a hypersphere. An analogy is the surface of an ordinary three-dimensional sphere, for example, a globe or the Earth. No matter how much a traveler travels across the Earth, he will never reach its edge. However, this does not mean that the Earth is infinite. The traveler will simply return to the place from which he began his journey.

On the surface of the hypersphere

Exactly the same space wanderer, crossing the Einstein Universe on a starship, can return back to Earth. Only this time the wanderer will move not along the two-dimensional surface of a sphere, but along the three-dimensional surface of a hypersphere. This means that the Universe has a finite volume, and therefore a finite number of stars and mass. However, the Universe has neither boundaries nor any center.

Einstein came to these conclusions by connecting space, time and gravity in his famous theory. Before him, these concepts were considered separate, which is why the space of the Universe was purely Euclidean. Einstein proved that gravity itself is a curvature of space-time. This radically changed early ideas about the nature of the Universe, based on classical Newtonian mechanics and Euclidean geometry.

Expanding Universe

Even the discoverer himself " new universe“was not a stranger to delusions. Although Einstein limited the Universe in space, he continued to consider it static. According to his model, the Universe was and remains eternal, and its size always remains the same. In 1922, Soviet physicist Alexander Friedman significantly expanded this model. According to his calculations, the Universe is not static at all. It can expand or contract over time. It is noteworthy that Friedman came to such a model based on the same theory of relativity. He managed to apply this theory more correctly, bypassing the cosmological constant.

Albert Einstein did not immediately accept this “amendment.” This new model came to the aid of the previously mentioned Hubble discovery. The recession of galaxies indisputably proved the fact of the expansion of the Universe. So Einstein had to admit his mistake. Now the Universe had a certain age, which strictly depends on the Hubble constant, which characterizes the rate of its expansion.

Further development of cosmology

As scientists tried to solve this question, many other important components of the Universe were discovered and various models of it were developed. So in 1948, George Gamow introduced the “hot Universe” hypothesis, which would later turn into the big bang theory. The discovery in 1965 confirmed his suspicions. Now astronomers could observe the light that came from the moment when the Universe became transparent.

Dark matter, predicted in 1932 by Fritz Zwicky, was confirmed in 1975. Dark matter actually explains the very existence of galaxies, galaxy clusters and the Universal structure itself as a whole. This is how scientists learned that most of the mass of the Universe is completely invisible.

Finally, in 1998, during a study of the distance to, it was discovered that the Universe is expanding at an accelerating rate. This latest turning point in science gave birth to our modern understanding of the nature of the universe. The cosmological coefficient, introduced by Einstein and refuted by Friedman, again found its place in the model of the Universe. The presence of a cosmological coefficient (cosmological constant) explains its accelerated expansion. To explain the presence of the cosmological constant, the concept was introduced - a hypothetical field containing most of the mass of the Universe.

Modern understanding of the size of the observable Universe

The modern model of the Universe is also called the ΛCDM model. The letter "Λ" means the presence of a cosmological constant, which explains the accelerated expansion of the Universe. "CDM" means that the Universe is filled with cold dark matter. Recent studies indicate that the Hubble constant is about 71 (km/s)/Mpc, which corresponds to the age of the Universe 13.75 billion years. Knowing the age of the Universe, we can estimate the size of its observable region.

According to the theory of relativity, information about any object cannot reach an observer at a speed greater than the speed of light (299,792,458 m/s). It turns out that the observer sees not just an object, but its past. The farther an object is from him, the more distant the past he looks. For example, looking at the Moon, we see as it was a little more than a second ago, the Sun - more than eight minutes ago, the nearest stars - years, galaxies - millions of years ago, etc. In Einstein's stationary model, the Universe has no age limit, which means its observable region is also not limited by anything. The observer, armed with increasingly sophisticated astronomical instruments, will observe increasingly distant and ancient objects.

We have a different picture with modern model Universe. According to it, the Universe has an age, and therefore a limit of observation. That is, since the birth of the Universe, no photon could have traveled a distance greater than 13.75 billion light years. It turns out that we can say that the observable Universe is limited from the observer to a spherical region with a radius of 13.75 billion light years. However, this is not entirely true. We should not forget about the expansion of the space of the Universe. By the time the photon reaches the observer, the object that emitted it will be already 45.7 billion light years away from us. years. This size is the horizon of particles, it is the boundary of the observable Universe.

Over the horizon

So, the size of the observable Universe is divided into two types. Apparent size, also called the Hubble radius (13.75 billion light years). And the real size, called the particle horizon (45.7 billion light years). The important thing is that both of these horizons do not at all characterize the real size of the Universe. Firstly, they depend on the position of the observer in space. Secondly, they change over time. In the case of the ΛCDM model, the particle horizon expands at a speed greater than the Hubble horizon. Modern science does not answer the question of whether this trend will change in the future. But if we assume that the Universe continues to expand with acceleration, then all those objects that we see now will sooner or later disappear from our “field of vision”.

Currently, the most distant light observed by astronomers is the cosmic microwave background radiation. Peering into it, scientists see the Universe as it was 380 thousand years after the Big Bang. At this moment, the Universe cooled down enough that it was able to emit free photons, which are detected today with the help of radio telescopes. At that time, there were no stars or galaxies in the Universe, but only a continuous cloud of hydrogen, helium and an insignificant amount of other elements. From the irregularities observed in this cloud, galaxy clusters will subsequently form. It turns out that precisely those objects that will be formed from inhomogeneities in the cosmic microwave background radiation are located closest to the particle horizon.

True Boundaries

Whether the Universe has true, unobservable boundaries is still a matter of pseudoscientific speculation. One way or another, everyone agrees on the infinity of the Universe, but interprets this infinity in completely different ways. Some consider the Universe to be multidimensional, where our “local” three-dimensional Universe is only one of its layers. Others say that the Universe is fractal - which means that our local Universe may be a particle of another. Don't forget about various models The Multiverse with its closed, open, parallel Universes, wormholes. And there are many, many different versions, the number of which is limited only by human imagination.

But if we turn on cold realism or simply step back from all these hypotheses, then we can assume that our Universe is an infinite homogeneous container of all stars and galaxies. Moreover, at any very distant point, be it billions of gigaparsecs from us, all the conditions will be exactly the same. At this point, the particle horizon and the Hubble sphere will be exactly the same, with the same relict radiation at their edge. There will be the same stars and galaxies around. Interestingly, this does not contradict the expansion of the Universe. After all, it is not just the Universe that is expanding, but its space itself. The fact that at the moment of the Big Bang the Universe arose from one point only means that the infinitely small (practically zero) dimensions that were then have now turned into unimaginably large ones. In the future, we will use precisely this hypothesis in order to clearly understand the scale of the observable Universe.

Visual representation

IN various sources All kinds of visual models are provided to help people understand the scale of the Universe. However, it is not enough for us to realize how big the cosmos is. It is important to imagine how concepts such as the Hubble horizon and the particle horizon actually manifest themselves. To do this, let's imagine our model step by step.

Let's forget that modern science does not know about the “foreign” region of the Universe. Discarding versions of multiverses, the fractal Universe and its other “varieties”, let’s imagine that it is simply infinite. As noted earlier, this does not contradict the expansion of its space. Of course, let's take into account that its Hubble sphere and particle sphere are respectively 13.75 and 45.7 billion light years.

Scale of the Universe

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First, let's try to understand how large the Universal scale is. If you have traveled around our planet, you can well imagine how big the Earth is for us. Now imagine our planet as a grain of buckwheat moving in orbit around a watermelon-Sun the size of half a football field. In this case, Neptune's orbit will correspond to the size small town, region - to the Moon, region of the boundary of the influence of the Sun - to Mars. It turns out that our Solar System is as much larger than the Earth as Mars is larger than buckwheat! But this is just the beginning.

Now let’s imagine that this buckwheat will be our system, the size of which is approximately equal to one parsec. Then the Milky Way will be the size of two football stadiums. However, this will not be enough for us. The Milky Way will also have to be reduced to centimeter size. It will somewhat resemble coffee foam wrapped in a whirlpool in the middle of coffee-black intergalactic space. Twenty centimeters from it there is the same spiral “crumb” - the Andromeda Nebula. Around them there will be a swarm of small galaxies of our Local Cluster. The apparent size of our Universe will be 9.2 kilometers. We have come to an understanding of the Universal dimensions.

Inside the universal bubble

However, it is not enough for us to understand the scale itself. It is important to realize the Universe in dynamics. Let's imagine ourselves as giants, for whom the Milky Way has a centimeter diameter. As noted just now, we will find ourselves inside a ball with a radius of 4.57 and a diameter of 9.24 kilometers. Let’s imagine that we are able to float inside this ball, travel, covering entire megaparsecs in a second. What will we see if our Universe is infinite?

Of course, countless galaxies of all kinds will appear before us. Elliptical, spiral, irregular. Some areas will be teeming with them, others will be empty. Main feature will be that visually they will all be motionless while we are motionless. But as soon as we take a step, the galaxies themselves will begin to move. For example, if we are able to see in centimeter Milky Way microscopic Solar System, then we can observe its development. Moving 600 meters away from our galaxy, we will see the protostar Sun and the protoplanetary disk at the moment of formation. Approaching it, we will see how the Earth appears, life arises and man appears. In the same way, we will see how galaxies change and move as we move away from or approach them.

Consequently, the more distant galaxies we look at, the more ancient they will be for us. So the most distant galaxies will be located further than 1300 meters from us, and at the turn of 1380 meters we will already see relict radiation. True, this distance will be imaginary for us. However, as we get closer to the cosmic microwave background radiation, we will see an interesting picture. Naturally, we will observe how galaxies will form and develop from the initial cloud of hydrogen. When we reach one of these formed galaxies, we will understand that we have covered not 1.375 kilometers at all, but all 4.57.

Zooming out

As a result, we will increase in size even more. Now we can place entire voids and walls in the fist. So we will find ourselves in a rather small bubble from which it is impossible to get out. Not only will the distance to objects at the edge of the bubble increase as they get closer, but the edge itself will shift indefinitely. This is the whole point of the size of the observable Universe.

No matter how big the Universe is, for an observer it will always remain a limited bubble. The observer will always be at the center of this bubble, in fact he is its center. Trying to get to any object at the edge of the bubble, the observer will shift its center. As you approach an object, this object will move further and further from the edge of the bubble and at the same time change. For example, from a shapeless hydrogen cloud it will turn into a full-fledged galaxy or, further, a galactic cluster. In addition, the path to this object will increase as you approach it, since the surrounding space itself will change. Having reached this object, we will only move it from the edge of the bubble to its center. At the edge of the Universe, relict radiation will still flicker.

If we assume that the Universe will continue to expand at an accelerated rate, then being in the center of the bubble and moving time forward by billions, trillions and even higher orders of years, we will notice an even more interesting picture. Although our bubble will also increase in size, its changing components will move away from us even faster, leaving the edge of this bubble, until each particle of the Universe wanders separately in its lonely bubble without the opportunity to interact with other particles.

So, modern science has no information about what actual sizes the Universe and whether it has boundaries. But we know for sure that the observable Universe has a visible and true boundary, called respectively the Hubble radius (13.75 billion light years) and the particle radius (45.7 billion light years). These boundaries depend entirely on the observer's position in space and expand over time. If the Hubble radius expands strictly at the speed of light, then the expansion of the particle horizon is accelerated. The question of whether its acceleration of the particle horizon will continue further and whether it will be replaced by compression remains open.

Einstein's general theory of relativity studies the geometry of 4-dimensional space-time. However, the question of the shape (geometry) of three-dimensional space itself remains unclear to this day.

By studying the distribution of galaxies, scientists came to the conclusion that our Universe, with high degree accuracy, is spatially homogeneous and isotropic on large scales. This means that the geometry of our world is the geometry of a homogeneous and isotropic three-dimensional manifold. There are only three such manifolds: a three-dimensional plane, a three-dimensional sphere and a three-dimensional hyperboloid. The first manifold corresponds to the usual three-dimensional Euclidean space. In the second case, the Universe has the shape of a sphere. This means that the world is closed, and we could get to the same point in space simply by moving in a straight line (like trip around the world on Earth). Finally, hyperboloid-shaped space corresponds to an open three-dimensional manifold, in which the sum of the angles of a triangle is always less than 180 degrees. Thus, studying only the large-scale structure of the Universe does not allow us to unambiguously determine the geometry of three-dimensional space, but significantly reduces the possible options.

The study of cosmic microwave background radiation, the most accurate cosmological observable at the moment, allows progress in this issue. The fact is that the shape of three-dimensional space has a significant impact on the propagation of photons in the Universe - even a slight curvature of the three-dimensional manifold would significantly affect the spectrum of the cosmic microwave background radiation. Modern research On this topic they say that the geometry of the Universe is flat with a high degree of accuracy. If space is curved, then the corresponding radius of curvature is 10,000 greater than the causally connected region in the Universe.

The question of the geometry of three-dimensional manifold is closely related to the evolution of the Universe in the future. For space in the form of a three-dimensional hyperboloid, the expansion of the Universe would last forever, while for spherical geometry the expansion would give way to compression, followed by the collapse of the Universe back into a singularity. However, based on modern data, the rate of expansion of the Universe today is determined not by the curvature of the three-dimensional manifold, but by dark energy, a certain substance with a constant density. Moreover, if the density of dark energy remains constant in the future, its contribution to the total density of the Universe will only increase with time, and the contribution of curvature will decrease. This means that the geometry of the three-dimensional manifold will likely never have a significant impact on the evolution of the Universe. Of course, it is impossible to make any reliable predictions about the properties of dark energy in the future, and only more accurate studies of its properties can shed light on the future fate of the Universe.