The diameter of the Moon is 3000 km, the diameter of the Earth is 12800 km, the Sun is 1.4 million km, while the distance from the Sun to the Earth is 150 million km. The diameter of Jupiter, the largest planet in our solar system, is 150,000 km. No wonder they say that Jupiter could be a star, in the video next to Jupiter is working star, its size () is even smaller than Jupiter. By the way, since we touched on Jupiter, you may not have heard, but Jupiter does not revolve around the Sun. The fact is that the mass of Jupiter is so large that the center of rotation of Jupiter and the Sun is outside the Sun, thus both the Sun and Jupiter rotate together around a common center of rotation.
According to some calculations, in our galaxy, which is called the "Milky Way" (Milky Way), there are 400 billion stars. This is far from the largest galaxy; there are more than a trillion stars in neighboring Andromeda.
As stated in the video at 4:35, in a few billion years our Milky Way will collide with Andromeda. According to some calculations, using any technology known to us, even improved in the future, we will not be able to fly to other galaxies, as they are constantly moving away from us. Only teleportation can help us. This is bad news.
The good news is that you and I were born at a good time when scientists see other galaxies and can theorize about the Big Bang and other phenomena. If we were born much later, when all the galaxies would have scattered far from each other, then most likely we would not have been able to find out how the universe arose, whether there were other galaxies, whether there was a Big Bang, etc. We would consider that our Milky Way (united by that time with Andromeda) is the only and unique in the entire cosmos. But we are lucky and we know something. Maybe.
Let's get back to the numbers. Our small Milky Way contains up to 400 billion stars, neighboring Andromeda has more than a trillion, and there are more than 100 billion such galaxies in the observable universe. And many of them contain several trillion stars. It may seem incredible that there are so many stars in space, but somehow the Americans took and pointed their mighty Hubble telescope at a completely empty space in our sky. After observing him for several days, they received this photo:
In a completely empty patch of our sky, they found 10 thousand galaxies (not stars), each of which contains billions and trillions of stars. Here is this square in our sky, for scale.
And what is happening outside the observable universe, we do not know. The size of the universe that we see is about 91.5 billion light years. What's next is unknown. Perhaps our entire universe is just a bubble in the seething ocean of multiverses. In which other laws of physics may even apply, for example, the law of Archimedes does not work and the sum of the angles is not equal to 360 gr.
Enjoy. Dimensions of the universe in the video:
The universe is everything that exists. The universe is limitless. Therefore, when discussing the size of the Universe, we can only talk about the size of its observable part - the observable Universe.
The observable Universe is a ball centered on the Earth (the place of the observer), has two dimensions: 1. apparent size - the Hubble radius - 13.75 billion light years, 2. real size - the radius of the particle horizon - 45.7 billion light years .
The modern model of the Universe is also called the ΛCDM model. The letter "Λ" means the presence of the cosmological constant, which explains the accelerated expansion of the Universe. "CDM" means that the universe is filled with cold dark matter. Recent studies suggest that the Hubble constant is about 71 (km/s)/Mpc, which corresponds to the age of the Universe at 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 the observer at a speed greater than the speed of light (299792458 km/s). It turns out, the observer sees not just the object, but its past. The farther the object is from it, the more distant past it looks. For example, looking at the Moon, we see the way 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 that its observable region is also not limited by anything. The observer, armed with more and more advanced astronomical instruments, will observe more and more distant and ancient objects.
Dimensions of the observable universe
We have a different picture with the modern model of the Universe. According to it, the Universe has an age, and hence the limit of observation. That is, since the birth of the Universe, no photon would have had time to travel 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 by a spherical region with a radius of 13.75 billion light years. However, this is not quite true. Do 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 45.7 billion light-years away from us. This size is the particle horizon, and it is the boundary of the observable Universe.
So, the size of the observable universe is divided into two types. The 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).
It is important that both of these horizons do not at all characterize the real size of the Universe. First, they depend on the position of the observer in space. Second, they change over time. In the case of the ΛCDM model, the particle horizon expands at a rate greater than the Hubble horizon. The question of whether this trend will change in the future, modern science does not give an answer. 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”.
At the moment, the most distant light observed by astronomers is. Looking into it, scientists see the Universe as it was 380,000 years after the Big Bang. At that moment, the Universe cooled down so much that it was able to emit free photons, which are captured 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 a negligible amount of other elements. From the inhomogeneities observed in this cloud, galactic clusters will subsequently form. It turns out that it is precisely those objects that will form from the inhomogeneities of the cosmic microwave background radiation that are located closest to the particle horizon.
The real size of the universe
So, we have decided on the size of the observable universe. But what about the actual size of the entire universe? modern science does not have information about the real size of the universe and whether it has boundaries. But most scientists agree that the universe is limitless.
Conclusion
The observable Universe has a visible and true boundary, called the Hubble radius (13.75 billion light years) and the particle radius (45.7 billion light years), respectively. These boundaries are completely dependent on the position of the observer in space and expand with 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.
In cosmology, there is still no clear answer to the question that affects the age, shape and size of the Universe, and there is no consensus about its finiteness. Because if the universe is finite, then it must either contract or expand. In the event that it is infinite, many assumptions lose their meaning.
Back in 1744, the 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 does the sky not sparkle and why is it dark? In 1823, G. Olbes argued the existence of the boundaries of the Universe by the fact that the light coming to the Earth from distant stars should become weaker due to absorption by the substance that is in their path. But in this case, this substance itself should heat up and glow no worse than any star. found its confirmation 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, in the event that the dimensions of the Universe are indeed infinite, then the light of stars that have reached the limiting distance has such a strong redshift that it begins to merge with the background (secondary) vacuum radiation.
At the same time, it can be said that the observed by mankind are finite, since the distance of 24 Gigaparsex itself is finite and is the boundary of the light cosmic horizon. However, due to the fact that it is increasing, the end of the universe is at a distance of 93 billion
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 conclude that the Big Bang theory is being confirmed. According to NASA,
which were obtained using WMAP, starting from the moment of the Big Bang, equals 13.7 billion years. However, this result is possible only if we assume that the model underlying the analysis is correct. When using other estimation methods, completely different data are obtained.
Touching upon the structure of the Universe, one cannot but say about its form. Until now, that three-dimensional figure has not been found that would best represent her image. This difficulty is due to the fact that it is still not known exactly whether the Universe is flat. The second aspect is related to the fact that it is not known for certain about its multiple connection. Accordingly, if the dimensions of the Universe are spatially limited, then when moving in a straight line and in any direction, one can end up at the starting point.
As we can see, technological progress has not yet reached the level to accurately answer questions regarding the age, structure and size of the universe. So far, many theories in cosmology have not been confirmed, but they have not been refuted either.
17:45 23/06/2016👁 916
The scale of the cosmos is difficult to imagine and even more difficult to accurately determine. But thanks to the ingenious insights of physicists, we think we have a good idea of how big the cosmos is. "Let's take a walk through" - such an invitation was made by American astronomer Harlow Shapley to an audience in Washington, DC, in 1920. He took part in the so-called Great Debate on the scale of the universe, along with colleague Heber Curtis.
Shapley believed that our galaxy was 300,000 across. This is three times more than they think 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.
In the early 20th century, however, 300,000 light-years seemed to many of Shapley's contemporaries some absurdly large number. And the idea that others like the Milky Way - which were visible in - were just as big, was generally not taken seriously.
Yes, and Shapley himself believed that the Milky Way should be special. "Even if the spirals are present, 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 pretty sure that the Milky Way is somewhere between 100,000 and 150,000 light years across. The observable universe is, of course, much larger. It is believed that its diameter is 93 billion light years. But why such confidence? How can you even measure something like that 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 shall 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 ingenious tools 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 this go through the scale of distances in astronomy. The first step of this scale is quite simple and relies on modern technology these days.
“We can just bounce radio waves off the nearest ones in the solar system, like and , and measure the time it takes for those waves to get back to Earth,” Casey says. “Measurements will thus be very accurate.”
Large radio telescopes like those in Puerto Rico can do the job - but they can also do more. Arecibo, for example, can detect those flying around our solar system and even create images of them, depending on how radio waves bounce off the asteroid's surface.
But using radio waves to measure distances outside of our solar system is impractical. The next step in this cosmic scale is the measurement of parallax. We do it all the time without even realizing it. Humans, like many animals, intuitively understand the distance between themselves and objects, thanks to the fact that we have two eyes.
If you hold an object in front of you - a 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 using a different sense: telescopes.
Imagine two eyes floating in space, on either side of our Sun. Thanks to the orbit of the Earth, we have these eyes, and we can observe the displacement of stars relative to objects in the background using this method.
“We measure the position of the stars in the sky in, say, January, and then we 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 - around 100 light-years - that the observed displacement 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 the 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 with age. By accurately measuring their color and brightness, and then comparing this to 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 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 that are used for this analysis are considered one of the types of "standard candles" - bodies whose magnitude (or brightness) we can calculate mathematically. These candles are scattered throughout the cosmos and illuminate the universe in a predictable way. But main sequence stars are not the only examples.
This understanding of how brightness is related to distance allows us to understand the distances to even more distant objects, like stars in other galaxies. The main sequence approach won't work anymore, because the light from these stars - which are millions of light-years away, if not more - is difficult to analyze accurately.
But in 1908, a scientist named Henrietta Swan Leavitt of Harvard made a fantastic discovery that helped us measure these colossal distances as well. Swan Leavitt realized that there is 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,” says Casey.
In other words, a brighter Cepheid star will "pulse" more slowly (over many days) than a dimmer Cepheid. Because astronomers can quite easily measure the pulse of a Cepheid, they can tell how bright a 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 the sense that brightness is the key. However, the important thing is that distance can be measured in a variety of 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 the nearest Cepheid and concluded that it was only a million light-years away.
Today, by our best estimate, this galaxy is 2.54 million light-years away. So Hubble was wrong. But this does not detract from his merits. Because we are still trying to calculate the distance to Andromeda. 2.54 million years is, in fact, 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 our galaxy is not limited.
Hubble also measured the brightness of exploding - type 1A. They can be seen in fairly distant galaxies, billions of light years away. Since the brightness of these calculations can be calculated, we can determine how far they are, as we did with the 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 really large distances. This is redshift.
If the siren of an ambulance or police car has ever rushed past you, you are familiar with the Doppler effect. When the ambulance approaches, the siren sounds louder, and when it moves away, the siren subsides again.
The same thing happens with waves of light, only on a small scale. We can fix this change by analyzing the light spectrum of distant bodies. There will be dark lines in this spectrum as individual colors are absorbed by elements in and around the light source - the surfaces of stars, for example.
The farther objects are from us, the further these lines will shift towards the red end of the spectrum. And this is not only because the objects are far from us, but because they are also moving away from us over time, due to the expansion of the Universe. And the observation of the redshift of light from distant galaxies, in fact, provides us with evidence that the Universe is indeed expanding.
Did you know that the universe we observe has pretty definite boundaries? We are accustomed to associate the Universe with something infinite and incomprehensible. However, modern science to the question of 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 the Universe cannot be infinite at all? It would seem that it is indisputable that the receptacle of everything that exists around us should not have boundaries. If these boundaries exist, what do they even represent?
Suppose some astronaut flew to the borders of the universe. What will he see before him? 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? It doesn't mean that there is "nothing". Emptiness and another Universe is also “something”. But the Universe is that which contains absolutely everything “something”.
We arrive at an absolute contradiction. It turns out that the border of the Universe should hide from us something that should not be. Or the boundary of the Universe should fence off “everything” from “something”, but this “something” should also be a part of “everything”. In general, complete absurdity. Then how can scientists claim the ultimate size, mass, and even age of our universe? These values, although unimaginably large, are still finite. Does science argue with the obvious? To deal with this, let's first look at how people came to the modern understanding of the universe.
Expanding the boundaries
From time immemorial, man has been interested in what the world around them is like. You can not give examples of the three whales 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 earthly firmament. Even in the times of antiquity and the Middle Ages, when astronomers had extensive knowledge of the laws of motion of the planets in the "fixed" celestial sphere, the Earth remained the center of the universe.
Naturally, even in Ancient Greece there were those who believed that the Earth revolves around the Sun. There were those who talked 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, the Polish astronomer Nicolaus Copernicus made the first major breakthrough in the 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 motion of the planets in the celestial sphere. In the case of a stationary Earth, astronomers had to come up with all sorts of ingenious theories to explain this behavior of the planets. On the other hand, if the Earth is assumed to be mobile, then the explanation for such intricate movements comes naturally. Thus, a new paradigm called "heliocentrism" was strengthened in astronomy.
Many Suns
However, even after that, 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 luminaries. For several centuries, astronomers have unsuccessfully tried to detect deviations in the position of stars relative to the Earth's orbital motion (annual parallaxes). The tools of those times did not allow for such accurate measurements.
Finally, in 1837, the Russian-German astronomer Vasily Struve measured the parallax. This marked a new step in understanding the scale of the cosmos. Now scientists could safely say that the stars are distant likenesses of 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 orbits of the planets seemed insignificant compared to this something. Next, it was necessary to understand how the stars are concentrated in.
Many Milky Ways
As early as 1755, the famous philosopher Immanuel Kant anticipated the foundations of the modern understanding of the large-scale structure of the universe. He hypothesized that the Milky Way is a huge rotating star cluster. In turn, many observable nebulae are also more distant "milky ways" - galaxies. Despite this, until the 20th century, astronomers adhered to the fact that all nebulae are sources of star formation and are part of the Milky Way.
The situation changed when astronomers learned to measure the distances between galaxies using. The absolute luminosity of stars of this type is strictly dependent on the period of their variability. 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 Shelpie. Thanks to him, the Soviet astronomer Ernst Epik 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 undertaking. 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 entrenched view that the Milky Way is the edge of the universe. It was now one of the many galaxies that had once considered it an integral part. Kant's hypothesis was confirmed almost two centuries after its development.
Subsequently, the connection between the distance of the galaxy from the observer and the speed of its removal from the observer, discovered by Hubble, made it possible to compile a complete picture of the large-scale structure of the Universe. It turned out that the galaxies were only a tiny part of it. They connected into clusters, clusters into superclusters. In turn, superclusters fold into the largest known structures in the universe - filaments and walls. These structures, adjacent to huge supervoids () and constitute a large-scale structure of the currently known universe.
Apparent infinity
From the foregoing, it follows 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 it was only about the scale of the cosmos, 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 someone expressed the idea of the infinity of the Universe, it was only in a philosophical key. Without any scientific justification. An example of this is Giordano Bruno. By the way, like Kant, he was ahead of science by many centuries. He was the first to declare that the stars are distant suns, and planets also revolve around them.
It would seem that the very fact of infinity is quite reasonable and obvious, but the turning points in science of the 20th century shook this “truth”.
Stationary Universe
The first significant step towards the development of a modern model of the universe was made by Albert Einstein. The famous physicist introduced his model of the stationary Universe in 1917. This model was based on the general theory of relativity, developed by him a year earlier. According to his model, the universe is infinite in time and finite in space. But after all, as noted earlier, according to Newton, a universe with a finite size must collapse. To do this, Einstein introduced the cosmological constant, which compensated for the gravitational attraction of distant objects.
No matter how paradoxical it may sound, Einstein did not limit the very finiteness 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 the traveler travels 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 where he started his journey.
On the surface of the hypersphere
In the same way, a space wanderer, overcoming the Einstein Universe on a starship, can return back to Earth. Only this time the wanderer will move not on the two-dimensional surface of the sphere, but on the three-dimensional surface of the hypersphere. This means that the Universe has a finite volume, and hence a finite number of stars and mass. However, the universe does not have any boundaries or any center.
Einstein came to such conclusions by linking 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 the 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. Einstein, although he 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, the Soviet physicist Alexander Fridman 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 such a "correction". To the aid of this new model came the previously mentioned discovery of Hubble. 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 problem, many other important components of the Universe were discovered and various models of it were developed. So in 1948, Georgy 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 very structure of the Universe as a whole. So scientists learned that most of the mass of the universe is completely invisible.
Finally, in 1998, during the study of the distance to, it was discovered that the Universe is expanding with acceleration. This next turning point in science gave rise to modern understanding of the nature of the universe. Introduced by Einstein and refuted by Friedmann, the cosmological coefficient 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.
The current idea of the size of the observable universe
The current model of the Universe is also called the ΛCDM model. The letter "Λ" means the presence of the cosmological constant, which explains the accelerated expansion of the Universe. "CDM" means that the universe is filled with cold dark matter. Recent studies suggest that the Hubble constant is about 71 (km/s)/Mpc, which corresponds to the age of the Universe at 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 the observer at a speed greater than the speed of light (299792458 m/s). It turns out that the observer sees not just an object, but its past. The farther the object is from it, the more distant past it looks. For example, looking at the Moon, we see the way 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 that its observable region is also not limited by anything. The observer, armed with more and more advanced astronomical instruments, will observe more and more 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 hence the limit of observation. That is, since the birth of the Universe, no photon would have had time to travel 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 by a spherical region with a radius of 13.75 billion light years. However, this is not quite true. Do not forget about the expansion of the space of the Universe. Until the photon reaches the observer, the object that emitted it will already be 45.7 billion light years away from us. years. This size is the particle horizon, and it is the boundary of the observable Universe.
Over the horizon
So, the size of the observable universe is divided into two types. The 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). It is important that both of these horizons do not at all characterize the real size of the Universe. First, they depend on the position of the observer in space. Second, they change over time. In the case of the ΛCDM model, the particle horizon expands at a rate greater than the Hubble horizon. The question of whether this trend will change in the future, modern science does not give an answer. 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”.
So far, the most distant light observed by astronomers is the CMB. Looking into it, scientists see the Universe as it was 380,000 years after the Big Bang. At that moment, the Universe cooled down so much that it was able to emit free photons, which are captured 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 a negligible amount of other elements. From the inhomogeneities observed in this cloud, galactic clusters will subsequently form. It turns out that it is precisely those objects that will form from the inhomogeneities of the cosmic microwave background radiation that are located closest to the particle horizon.
True Borders
Whether the universe has true, unobservable boundaries is still the subject of pseudoscientific speculation. One way or another, everyone converges on the infinity of the Universe, but they interpret this infinity in completely different ways. Some consider the Universe to be multidimensional, where our "local" three-dimensional Universe is just one of its layers. Others say that the Universe is fractal, which means that our local Universe may be a particle of another. Do not forget about the various models of the Multiverse with its closed, open, parallel Universes, wormholes. And many, many more different versions, the number of which is limited only by human imagination.
But if we turn on cold realism or simply move away from all these hypotheses, then we can assume that our Universe is an endless homogeneous container of all stars and galaxies. Moreover, at any very distant point, whether it be in 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. Around will be the same stars and galaxies. Interestingly, this does not contradict the expansion of the universe. After all, it is not just the Universe that is expanding, but its very space. The fact that at the moment of the big bang the Universe arose from one point only says that the infinitely small (practically zero) sizes that were then have now turned into unimaginably large ones. In the future, we will use this hypothesis in order to clearly understand the scale of the observable Universe.
Visual representation
Various sources provide all sorts of visual models that allow people to realize the scale of the universe. However, it is not enough for us to realize how vast the cosmos is. It is important to understand how such concepts as the Hubble horizon and the particle horizon actually manifest. 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 the versions about the 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, we take into account the fact that its Hubble sphere and the sphere of particles are respectively 13.75 and 45.7 billion light years.
The scale of the universe
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To begin with, let's try to realize how large the Universal scales are. 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, which moves in orbit around the watermelon-Sun, the size of half a football field. In this case, the orbit of Neptune will correspond to the size of a small city, the area - to the Moon, the area 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 only the beginning.
Now 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. We will have to reduce the Milky Way to a centimeter size. It will somehow resemble coffee foam wrapped in a whirlpool in the middle of coffee-black intergalactic space. Twenty centimeters from it, there is the same spiral "baby" - the Andromeda Nebula. Around them will be a swarm of small galaxies in our Local Cluster. The apparent size of our universe will be 9.2 kilometers. We have come to understand 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. 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. Imagine that we are able to soar inside this ball, travel, overcoming whole megaparsecs in a second. What will we see if our universe is infinite?
Of course, before us will appear countless all kinds of galaxies. 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 will be motionless. But as soon as we take a step, the galaxies themselves will begin to move. For example, if we are able to see the microscopic Solar System in the centimeter Milky Way, we can observe its development. Having moved away from our galaxy by 600 meters, we will see the protostar Sun and the protoplanetary disk at the time of formation. Approaching it, we will see how the Earth appears, life is born 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 peer into, 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 relic radiation. True, this distance will be imaginary for us. However, as we get closer to the CMB, 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 overcome not 1.375 kilometers at all, but all 4.57.
Downscaling
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 the objects on the edge of the bubble increase as they approach, but the edge itself will move indefinitely. This is the whole point of the size of the observable universe.
No matter how big the Universe is, for the 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 some object on the edge of the bubble, the observer will shift its center. As you approach the object, this object will move further and further away 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, as the surrounding space itself will change. When we get to this object, we will only move it from the edge of the bubble to its center. At the edge of the Universe, the relic radiation will also flicker.
If we assume that the Universe will continue to expand at an accelerated rate, then being in the center of the bubble and winding time for billions, trillions and even higher orders of years ahead, we will notice an even more interesting picture. Although our bubble will also increase in size, its mutating components will move away from us even faster, leaving the edge of this bubble, until every particle of the Universe wanders apart in its lonely bubble without the ability to interact with other particles.
So, modern science does not have information about what the real dimensions of the universe are and whether it has boundaries. But we know for sure that the observable Universe has a visible and true boundary, called the Hubble radius (13.75 billion light years) and the particle radius (45.7 billion light years), respectively. These boundaries are completely dependent on the position of the observer in space and expand with 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 particle horizon acceleration will continue further and change to contraction remains open.
