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, when asked about the “infinity” of the Universe, offers a completely different answer to such an “obvious” question.
According to modern concepts, 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 the mind of an ordinary person is 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 revolved 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 greater than the size of the 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 it was one of many galaxies that had once been considered part of it. Kant's hypothesis was confirmed almost two centuries after its development.
Subsequently, the connection between the distance of a galaxy from an observer and the speed of its removal from him, discovered by Hubble, 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 - filaments and walls. These structures, adjacent to huge supervoids (), constitute the large-scale structure of the currently known 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
In the same way, a space wanderer, traversing Einstein’s 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 of the “new Universe” himself 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, depending on the Hubble constant, characterizing 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 the modern model of the 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 quite 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 inhomogeneities 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. We should not forget about the various models of the Multiverse with its closed, open, parallel Universes, and 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 (almost zero) sizes that were then have now turned into unimaginably large ones. In the future, we will use precisely this hypothesis in order to understand the scale of the observable Universe.
Visual representation
Various sources provide all sorts of visual models that allow people to 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 appear. 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 the Hubble sphere and the 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 of a small city, the area will correspond to the Moon, and the area of the border of the Sun's influence will correspond 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 will be 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. The 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 discern a microscopic Solar System in the centimeter-long Milky Way, we will be able to 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 the 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 does not have information about the real size of 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.
You probably think that the universe is infinite? May be so. It is unlikely that we will ever know this for sure. It will not be possible to take in our entire universe with a glance. Firstly, this fact follows from the concept of the “big bang”, which states that the universe has its own birthday, so to speak, and, secondly, from the postulate that the speed of light is a fundamental constant. By now, the observable universe, which is 13.8 billion years old, has expanded in all directions to a distance of 46.1 billion light years. The question arises: what was the size of the universe then, 13.8 billion years ago? This question was asked to us by someone Joe Muscarella. Here's what he writes:
“I have seen different answers to the question of what the size of our universe was shortly after the period of cosmic inflation ended. One source says 0.77 centimeters, another says it's the size of a soccer ball, and a third says it's larger than the size of the observable universe. So which one is it? Or maybe something in between?”
Context
The Big Bang and the Black Hole
Die Welt 02/27/2015How the Universe created man
Nautilus 01/27/2015 By the way, the past year just gives us a reason to talk about Einstein and the essence of space-time, because last year we celebrated the centenary of the general theory of relativity. So let's talk about the universe.When we observe distant galaxies through a telescope, we can determine some of their parameters, for example the following:
— redshift (i.e. how much the light emitted by them has shifted relative to the inertial frame of reference);
— object brightness (i.e. measure the amount of light emitted by a distant object);
— angular radius of the object.
These parameters are very important, because if the speed of light is known (one of the few parameters that we know), as well as the brightness and size of the observed object (we also know these parameters), then the distance to the object itself can be determined.
In fact, you have to be content with only approximate characteristics of the brightness of the object and its size. If an astronomer observes a supernova explosion in some distant galaxy, then the corresponding parameters of other supernovae located in the neighborhood are used to measure its brightness; we assume that the conditions under which these supernovae erupted are similar, and that there is no interference between the observer and the space object. Astronomers identify the following three types of factors that determine the observation of a star: stellar evolution (the difference between objects depending on their age and distance), an exogenous factor (if the real coordinates of the observed objects differ significantly from the hypothetical ones) and an interference factor (if, for example, the passage of light are influenced by interference, such as dust) - and this is all in addition to other factors unknown to us.
By measuring the brightness (or size) of the observed object, using the brightness/distance ratio, you can determine the distance of the object from the observer. Moreover, from the redshift characteristics of an object, one can determine the extent of the expansion of the universe during the time during which the light from the object reaches the Earth. Using the relationship between matter-energy and space-time, which is explained by Einstein's general theory of relativity, we can consider all possible combinations of different forms of matter and energy that are currently available in the universe.
But that is not all!
If you know what parts the universe consists of, then using extrapolation you can determine its size, as well as find out what happened at any stage of the evolution of the universe, and what the energy density was at that time. As you know, the universe consists of the following components:
— 0.01% — radiation (photons);
- 0.1% - neutrinos (heavier than photons, but a million times lighter than electrons);
- 4.9% - ordinary matter, including planets, stars, galaxies, gas, dust, plasma and black holes;
- 27% - dark matter, i.e. its type that participates in gravitational interaction, but differs from all particles of the Standard Model;
— 68% — dark energy, which causes the expansion of the universe.
As you can see, dark energy is an important thing; it was discovered quite recently. For the first nine billion years of its history, the universe consisted primarily of matter (a combination of ordinary matter and dark matter). However, for the first few millennia, radiation (in the form of photons and neutrinos) was an even more important building block than matter!
Note that each of these components of the universe (i.e. radiation, matter and dark energy) has a different effect on the rate of its expansion. Even if we know that the universe is 46.1 billion light years in extent, we must know the exact combination of its constituent elements at each stage of its evolution in order to calculate the size of the universe at any point in time in the past.
- when the universe was about three years old, the diameter of the Milky Way was one hundred thousand light years;
- when the universe was one year old, it was much hotter and denser than it is now; the average temperature exceeded two million degrees Kelvin;
- one second after its birth, the universe was too hot for stable nuclei to form in it; at that moment, protons and neutrons were floating in a sea of hot plasma. In addition, at that time, the radius of the universe (if we take the Sun as the center of the circle) was such that only seven of all the currently existing star systems closest to us could fit into the described circle, the most distant of which would be Ross 154 (Ross 154 - a star in the constellation Sagittarius, distance 9.69 light years from the Sun - approx. lane);
- when the age of the universe was only one trillionth of a second, its radius did not exceed the distance from the Earth to the Sun; in that era, the expansion rate of the universe was 1029 times greater than it is now.
If you wish, you can see what happened at the final stage of inflation, i.e. just before the Big Bang. To describe the state of the universe at the earliest stage of its birth, one could use the singularity hypothesis, but thanks to the inflation hypothesis, the need for a singularity disappears completely. Instead of a singularity, we are talking about a very rapid expansion of the universe (i.e., inflation) occurring for some time before the hot, dense expansion that gave rise to the current universe. Now let's move on to the final stage of inflation of the universe (the time interval between 10 to minus 30 - 10 to minus 35 seconds). Let's look at what the size of the universe was when inflation stopped and the big bang happened.
Here we are talking about the observable part of the universe. Its true size is certainly much larger, but we don't know how much. To the best approximation (based on the data contained in the Sloan Digital Sky Survey (SDSS) and information obtained from the Planck space observatory), if the universe bends and folds, then the observable part of it is so indistinguishable from the “unwarped” one that the entire its radius must be at least 250 times the radius of the observed part.
In truth, the universe may even be infinite in extent, since how it behaved during the early stages of inflation is unknown to us except for the last fraction of a second. But if we talk about what happened during inflation in the observable part of the universe at the very last moment (between 10 minus 30 and 10 minus 35 seconds) before the Big Bang, then we know the size of the universe: it varies between 17 centimeters (at 10 at minus 35 seconds) and 168 meters (at 10 at minus 30 seconds).
What is seventeen centimeters? That's almost the diameter of a soccer ball. So, if you want to know which of the indicated sizes of the universe is closest to the real one, then stick to this figure. What if we assume dimensions smaller than a centimeter? This is too little; however, if we take into account the limitations imposed by cosmic microwave radiation, it turns out that the expansion of the universe could not end at such a high energy level, and therefore the size of the universe mentioned above at the very beginning of the “Big Bang” (i.e., a size not exceeding a centimeter ) excluded. If the size of the universe exceeded the current one, then in this case it makes sense to talk about the existence of an unobservable part of it (which is probably correct), but we have no way to measure this part.
So, what was the size of the universe at the time of its origin? If you believe the most authoritative mathematical models describing the stage of inflation, it turns out that the size of the universe at the time of its origin will fluctuate somewhere between the size of a human head and a city block built up with skyscrapers. And there, you see, only some 13.8 billion years will pass - and the universe in which we live appeared.
The size of the Universe is incomprehensibly large for us. Everything that surrounds us, and we ourselves, are just grains of this comprehensive concept. And it itself has not so much astronomical as philosophical overtones.
The philosophical part of the universe includes the entire material world existing in nature, which has no boundaries in time and space. It is represented by different forms and states taken by matter as a result of its development.
Scientists consider everything that exists to be the astronomical part of the universe: space, matter, time, energy. It also includes planets, stars, and all other possible cosmic bodies. Scientists can only partially understand the size of the Universe. And researchers cannot find an accurate and succinct definition for it. Perhaps it is equivalent to God or other manifestations of the Supreme Mind.
Scale of the Universe
In order to get even a little closer to answering the question of what the size of the Universe is, it is necessary to estimate the scale of its individual parts. For a person to circumnavigate the globe, it is a difficult task, but quite feasible. Now imagine that our planet compared to Saturn is like a coin compared to a basketball. And in relation to the Sun, the Earth generally looks like a small grain.
The entire Solar System also does not have a significant extent on the scale of the Universe. If we consider the limit of the system, its extent is about 120 astronomical units. At the same time, for one a.u. take a distance of ~ 150 billion km. Now imagine that the diameter of the entire Milky Way galaxy, of which the Sun and its surrounding planets are part, is 1 quintillion kilometers. This is a number with 18 zeros. And the cluster of different celestial bodies itself contains, according to various estimates, from 2 * 10 11 to 4 * 10 11 stars, most of which exceed our celestial body in size.
And the Milky Way is not the only galaxy in all of outer space. In the starry sky of the Earth, you can see the neighboring star clusters with the naked eye: Andromeda, the Large and Small Magellanic clouds. Distances to them are measured in megaparsecs—millions of light years. And each of them also extends to distances unimaginable for the human mind.
All clusters of stars are grouped into large-scale associations - groups of galaxies. For example, the Milky Way and neighboring formations are included in the Local Group with a diameter of about 1 megaparsec. Imagine, for a ray of light to travel from one end to the other, it will take 3.2 million years.
But this value is not the largest. Groups of galaxies, in turn, are united into superclusters or superclusters. These large-scale universe structures contain hundreds and thousands of galactic groups and millions of star formations. Thus, in the Virgo Supercluster, which includes the Milky Way, there are more than 100 groups of galaxies. The length of this structure is more than 200 million light years and this is only part of the giant Laniakea formation.
The center of gravity of Laniakea is the Great Attractor supercluster, attracting all other structures of this part of outer space. It can be safely called the center of the Universe, with the caveat that this is only the core of the cosmos we know. All of Laniakea has a diameter of more than 500 million light years. And, in order to finally understand the scale of the Universe, imagine that this gigantic formation is just that small part of the cosmos that a person could survey and imagine.
The visible Universe and its dimensions
The Visible or Observable Universe is a very complex concept. According to the theory of the Soviet geophysicist Friedman, all outer space is now in the stage of expansion. At the same time, all its elements move away from each other at superluminal speed. Relative to the Earth, the visible part of the universal expanses is that area of boundless space from which radiation can reach us. At the same time, the object itself emitting the signal could already have acquired a superluminal speed of removal from our galaxy, but we are still registering radiation from it.
What is the size of the Visible Universe? The boundary of the observable part of space is the cosmological horizon. All universal structures located outside this region emit radiation that does not reach the Solar System. However, the exact dimensions of the visible part of the Universe are very difficult to establish due to its constantly accelerating expansion.
If we take our stellar system as the center of the observable part of space, and the surface of the last scattering of the cosmic microwave background radiation as the cosmological horizon, then this entire sphere will be 93 billion light years in diameter. Its constituent structure is the Metagalaxy - a region of outer space accessible to study with modern astronomical instruments. The metagalaxy is homogeneous and isotropic, and researchers are still arguing whether it is the entire Universe or just a small part of it. Its extent is constantly changing due to improvements in technology used by astronomers.
What is space and what are its dimensions?
When talking about the size of the Universe, one cannot fail to mention the concept of “space”. This term refers to a part of the universal expanses filled with emptiness, lying outside the atmospheres and shells of celestial bodies. Space is not empty or hollow. It is filled with interstellar matter consisting of molecules of hydrogen, oxygen, as well as ionizing and electromagnetic radiation. In addition, there is dark matter, which scientists have been arguing about for several centuries. Many of them put forward the hypothesis that this hidden mass is the connecting link of outer space.
Modern astronomers, taking our planet as a starting point, distinguish:
- Near space. For humans, it begins at an altitude of about 19 kilometers. This is the Armstrong line where water boils at human body temperature. A person who is at this altitude without a spacesuit begins to boil with saliva and tears. An altitude of just 100 kilometers is considered the international official limit, after which outer space begins.
- Near-Earth space is considered such up to an altitude of about 260 thousand kilometers. This is the height to which the gravity of the Earth exceeds the gravity of the Sun. Our cosmonauts make orbital flights and various satellites fly in the range of these altitudes.
- Interplanetary region. At these altitudes, or rather distances from the Earth, it makes its flight around our planet. Only robotic space stations and NASA astronauts flew these distances during the 1970 Moon landing.
- Interstellar space - distance from Earth is already measured in billions of kilometers.
- Intergalactic space, where the distance is about 5 quintillion kilometers. All this is insignificant considering the size of the universe.
How big is the world?
After everything you’ve read, it’s worth thinking about how huge the world in which we live is. People are just microbes compared only to, not to mention galaxies and space. Moreover, the size of the Universe is inconceivable. And it is unlikely that we will ever be able to know it.
17:45 23/06/20160 👁 1 384
The scale of space is difficult to imagine and even more difficult to accurately determine. But thanks to the ingenious guesses of physicists, we think we have a good idea of how big the cosmos is. “Let us take a walk around,” was the invitation American astronomer Harlow Shapley made to an audience in Washington, D.C., in 1920. He took part in the so-called Great Debate on the scale of the Universe, along with his colleague Heber Curtis.
Shapley believed that our galaxy was 300,000 in diameter. This is three times more than is thought now, but for that time the measurements were quite good. In particular, he calculated the generally correct proportional distances within the Milky Way - our position relative to the center, for example.
At the beginning of the 20th century, however, 300,000 light years seemed to many of Shapley's contemporaries to be some kind of absurdly large number. And the idea that others like the Milky Way - which were visible in - were as large was not taken seriously at all.
And Shapley himself believed that the Milky Way should be special. “Even if the spirals are represented, they are not comparable in size to our star system,” he told his listeners.
Curtis disagreed. He thought, and rightly so, that there were many other galaxies in the Universe, scattered like ours. But his starting point was the assumption that the Milky Way was much smaller than Shapley had calculated. According to Curtis's calculations, the Milky Way was only 30,000 light-years in diameter - or three times smaller than modern calculations show.
Three times more, three times less - we are talking about such huge distances that it is quite understandable that astronomers who thought about this topic a hundred years ago could be so wrong.
Today we are fairly confident that the Milky Way is somewhere between 100,000 and 150,000 light years across. The observable Universe is, of course, much, much larger. It is believed to be 93 billion light years in diameter. But why such confidence? How can you even measure something like this with ?
Ever since Copernicus declared that the Earth is not the center, we have always struggled to rewrite our ideas about what the Universe is - and especially how big it can be. Even today, as we will see, we are gathering new evidence that the entire Universe may be much larger than we recently thought.
Caitlin Casey, an astronomer at the University of Texas at Austin, studies the universe. She says astronomers have developed a set of sophisticated instruments and measurement systems to calculate not only the distance from Earth to other bodies in our solar system, but also the gaps between galaxies and even to the very end of the observable universe.
The steps to measuring all of this go through the distance scale of astronomy. The first stage of this scale is quite simple and these days relies on modern technology.
“We can simply bounce radio waves off nearby ones in the solar system, like and, and measure the time it takes for those waves to return to Earth,” Casey says. “The measurements will thus be very accurate.”
Large radio telescopes like the one in Puerto Rico can do this job - but they can also do more. Arecibo, for example, can detect and even image those flying around our solar system, depending on how radio waves bounce off the asteroid's surface.
But using radio waves to measure distances beyond our solar system is impractical. The next step in this cosmic scale is the measurement of parallax. We do this all the time without even realizing it. Humans, like many animals, intuitively understand the distance between themselves and objects due to the fact that we have two eyes.
If you hold an object in front of you - your hand, for example - and look at it with one eye open, and then switch to the other eye, you will see your hand move slightly. This is called parallax. The difference between these two observations can be used to determine the distance to the object.
Our brains do this naturally with information from both eyes, and astronomers do the same with nearby stars, only they use a different sense: telescopes.
Imagine two eyes floating in space, on either side of our Sun. Thanks to the Earth's orbit, we have these eyes, and we can observe the displacement of stars relative to objects in the background using this method.
“We measure the positions of stars in the sky in, say, January, and then wait six months and measure the positions of the same stars in July when we are on the other side of the Sun,” Casey says.
However, there is a threshold beyond which objects are already so far away - about 100 light years - that the observed shift is too small to provide a useful calculation. At this distance we will still be far from the edge of our own galaxy.
The next step is main sequence installation. It relies on our knowledge of how stars of a certain size - known as main sequence stars - evolve over time.
First, they change color, becoming redder as they age. By accurately measuring their color and brightness, and then comparing this with what is known about the distance to main sequence stars, as measured by trigonometric parallax, we can estimate the position of these more distant stars.
The principle behind these calculations is that stars of the same mass and age would appear equally bright to us if they were at the same distance from us. But since this is often not the case, we can use the difference in measurements to figure out how far they really are.
The main sequence stars used for this analysis are considered to be one of the types of "standard candles" - bodies whose magnitude (or brightness) we can calculate mathematically. These candles are scattered throughout space and predictably illuminate the Universe. But main sequence stars are not the only examples.
This understanding of how brightness relates to distance allows us to understand distances to even more distant objects - like stars in other galaxies. The main sequence approach will no longer work because the light from these stars - which are millions of light years away, if not more - is difficult to accurately analyze.
But in 1908, a scientist named Henrietta Swan Leavitt from Harvard made a fantastic discovery that helped us measure these colossal distances. Swan Leavitt realized that there was a special class of stars - .
"She noticed that a certain type of star changes its brightness over time, and this change in brightness, in the pulsation of these stars, is directly related to how bright they are by nature," Casey says.
In other words, a brighter Cepheid star will "pulse" more slowly (over many days) than a fainter Cepheid. Because astronomers can quite easily measure the Cepheid's pulse, they can tell how bright the star is. Then, by observing how bright it appears to us, they can calculate its distance.
This principle is similar to the main sequence approach in that brightness is key. However, the important thing is that distance can be measured in different ways. And the more ways we have to measure distances, the better we can understand the true scale of our cosmic backyard.
It was the discovery of such stars in our own galaxy that convinced Harlow Shapley of its large size.
In the early 1920s, Edwin Hubble discovered a Cepheid at the nearest one and concluded that it was only a million light years away.
Today, our best estimate is that this galaxy is 2.54 million light-years away. Therefore, Hubble was wrong. But this in no way detracts from his merits. Because we're still trying to calculate the distance to Andromeda. 2.54 million years - this number is essentially the result of relatively recent calculations.
Even now, the scale of the Universe is difficult to imagine. We can estimate it, and very well, but, in truth, it is very difficult to accurately calculate the distances between galaxies. The universe is incredibly big. And it is not limited to our galaxy.
Hubble also measured the brightness of the exploding type 1A. They can be seen in fairly distant galaxies, billions of light years away. Because the brightness of these calculations can be calculated, we can determine how far away they are, just as we did with Cepheids. Type 1A supernovae and Cepheids are examples of what astronomers call standard candles.
There is another feature of the Universe that can help us measure truly large distances. This is redshift.
If you've ever heard the siren of an ambulance or police car rush past you, you're familiar with the Doppler effect. When the ambulance approaches, the siren sounds shriller, and when it moves away, the siren fades again.
The same thing happens with light waves, only on a small scale. We can detect this change by analyzing the light spectrum of distant bodies. There will be dark lines in this spectrum because individual colors are absorbed by elements in and around the light source - the surfaces of stars, for example.
The further objects are from us, the further towards the red end of the spectrum these lines will shift. And this is not only because objects are far from us, but because they are also moving away from us over time, due to the expansion of the Universe. And observing the redshift of light from distant galaxies actually provides us with evidence that the Universe is indeed expanding.
In cosmology, there is still no clear answer to the question that affects the age, shape and size of the Universe, and there is also no consensus on its finitude. Because if the Universe is finite, then it must either contract or expand. If it is infinite, many assumptions become meaningless.
Back in 1744, astronomer J.F. Shezo was the first to doubt that the Universe
Infinite: after all, if the number of stars has no limits, then why doesn’t the sky sparkle and why is it dark? In 1823, G. Albes argued for the existence of boundaries of the Universe by the fact that light coming to the Earth from distant stars should become weaker due to absorption by matter that is in their path. But in this case, this substance itself should heat up and glow no worse than any star. has been confirmed in modern science, which claims that the vacuum is “nothing”, but at the same time it has real physical properties. Of course, absorption by vacuum leads to an increase in its temperature, which results in the fact that vacuum becomes a secondary source of radiation. Therefore, if the dimensions of the Universe are indeed infinite, then the light of stars that have reached the maximum distance has such a strong red shift that it begins to merge with the background (secondary) radiation of the vacuum.
At the same time, we can say that what is observable by humanity is finite, since the distance itself of 24 Gigaparsex is finite and is the boundary of the light cosmic horizon. However, due to what is increasing, the end of the universe is 93 billion away
The most important result of cosmology was the fact of the expansion of the Universe. It was obtained from redshift observations and then quantified according to Hubble's law. This led scientists to the conclusion that the Big Bang theory is being confirmed. According to NASA,
which were obtained using WMAP, starting from the moment of the Big Bang, is equal to 13.7 billion years. However, this result is only possible if we assume that the model that underlies the analysis is correct. When using other assessment methods, completely different data are obtained.
Touching upon the structure of the Universe, one cannot help but say about its form. The three-dimensional figure that would best represent her image has not yet been found. This complexity is due to the fact that it is still not known for sure whether the Universe is flat. The second aspect is related to the fact that it is not known for certain about its multiple connections. Accordingly, if the size of the Universe is spatially limited, then when moving in a straight line and in any direction, you can end up at the starting point.
As we see, technical progress has not yet reached the level to accurately answer questions regarding the age, structure and size of the Universe. Until now, many theories in cosmology have not been confirmed, but have not been refuted either.