Hero of the Soviet era: the history of a worker Georgy Aleksandrovich Kalinyak (1910-09/14/1989) Born in 1910 in Grodno. In 1927 he graduated from the 7th grade of the Vitebsk secondary school. Since 1928 he lived in Leningrad. In 1928 he began working in the Kozhmetalloshtamp artel as a press operator, then from 1929 to

P. Soldatenkov - “Love Story, Disease Story” There is nothing more boring than talking about other people’s illnesses and other people’s fornication. Anna Akhmatova I don’t like it when respectable creative people talk about how he drank. I understand that he was drinking, but they bring it to the forefront like

Stephen Hawking

A BRIEF HISTORY OF TIME:

FROM THE BIG BANG TO BLACK HOLES

© Stephen Hawking, 1988, 1996

© AST Publishing House LLC, 2019 (design, translation into Russian)

Preface

I did not write the preface to the first edition of A Brief History of Time. Carl Sagan did it. Instead, I added a short section called “Acknowledgments,” where I was encouraged to express my gratitude to everyone. True, some of the charitable foundations that supported me were not very happy that I mentioned them - they received many more applications.

I think that no one - not the publisher, not my agent, not even myself - expected the book to be such a success. It made it onto the London newspaper's bestseller list. Sunday Times as many as 237 weeks - this is more than any other book (naturally, not counting the Bible and the works of Shakespeare). It was translated into about forty languages ​​and sold in huge numbers - for every 750 inhabitants of the Earth, men, women and children, there is approximately one copy. As Nathan Myhrvold of the firm noted Microsoft(this is my former graduate student), I have sold more books on physics than Madonna has sold books on sex.

The success of A Brief History of Time means that people are very interested in fundamental questions about where we came from and why the universe is the way we know it.

I took advantage of the opportunity presented to me to supplement the book with newer observational data and theoretical results that were obtained after the release of the first edition (April 1, 1988, on April Fool's Day). I've added a new chapter on wormholes and time travel. It appears that Einstein's general theory of relativity allows for the possibility of creating and maintaining wormholes—small tunnels connecting different regions of space-time. In this case, we could use them to quickly move around the Galaxy or to travel back in time. Of course, we have not yet met a single alien from the future (or maybe we have?), but I will try to guess what the explanation for this might be.

I will also discuss recent progress in the search for “duality,” or correspondence, between seemingly different physical theories. These correspondences are serious evidence in favor of the existence of a unified physical theory. But they also suggest that the theory may not be formulated in a consistent, fundamental way. Instead, in different situations one has to be content with different “reflections” of the underlying theory. Likewise, we cannot depict the entire earth's surface in detail on one map and are forced to use different maps for different areas. Such a theory would be a revolution in our ideas about the possibility of unifying the laws of nature.

However, it would in no way affect the most important thing: the Universe is subject to a set of rational laws that we are able to discover and comprehend.

As for the observational aspect, the most important achievement here, of course, was the measurement of fluctuations of the cosmic microwave background radiation within the framework of the project COBE(English) Cosmic Background Explorer –"Cosmic Background Radiation Researcher") 1
Fluctuations, or anisotropies, of the cosmic microwave background radiation were first discovered by the Soviet Relict project. – Note scientific ed.

And others. These fluctuations are, in essence, the “seal” of creation. We are talking about very small inhomogeneities in the early Universe, which was otherwise quite homogeneous. Subsequently, they turned into galaxies, stars and other structures that we observe through a telescope. The forms of fluctuations are consistent with the predictions of a model of the Universe that has no boundaries in the imaginary time direction. But in order to prefer the proposed model to other possible explanations for CMB fluctuations, new observations will be required. In a few years it will become clear whether our Universe can be considered completely closed, without beginning and end.

Stephen Hawking

Chapter first. Our picture of the Universe

One day a famous scientist (they say it was Bertrand Russell) gave a public lecture on astronomy. He talked about how the Earth moves in orbit around the Sun and how the Sun, in turn, moves in orbit around the center of a huge cluster of stars called our Galaxy. When the lecture ended, a small elderly woman in the back row of the audience stood up and said: “Everything that was said here is complete nonsense. The world is a flat plate on the back of a giant turtle." The scientist smiled condescendingly and asked: “What is that turtle standing on?” “You are a very smart young man, very smart,” the lady answered. “A turtle stands on another turtle, and that turtle stands on the next one, and so on ad infinitum!”

Most would consider it ridiculous to try to pass off our Universe as an infinitely tall tower of turtles. But why are we so sure that our idea of ​​the world is better? What do we really know about the Universe and how do we know all this? How did the Universe originate? What does the future hold for her? Did the Universe have a beginning, and if so, what came before it? What is the nature of time? Will it ever end? Is it possible to go back in time? Some of these long-standing questions are being answered by recent breakthroughs in physics, thanks in part to the advent of fantastic new technologies. Someday we will find new knowledge as obvious as the fact that the Earth revolves around the Sun. Or maybe as absurd as the idea of ​​a tower of turtles. Only time (whatever that is) will tell.

A long time ago, 340 years BC, the Greek philosopher Aristotle wrote a treatise “On Heaven”. In it, he put forward two convincing proofs that the Earth is spherical and not at all flat, like a plate. First, he realized that the cause of lunar eclipses is the passage of the Earth between the Sun and the Moon. The shadow cast by the Earth on the Moon is always round in shape, and this is only possible if the Earth is also round. If the Earth were shaped like a flat disk, the shadow would typically be elliptical; It would be round only if the Sun during an eclipse was located exactly under the center of the disk. Secondly, the ancient Greeks knew from the experience of their travels that in the south the North Star is located closer to the horizon than when observed in areas located to the north. (Since the North Star is located above the North Pole, an observer at the North Pole sees it directly overhead, and an observer near the equator sees it just above the horizon.) Moreover, Aristotle, based on the difference in the apparent position of the North Star during observations in Egypt and Greece, was able to estimate the circumference of the Earth at 400,000 stadia. We do not know exactly what one stade was equal to, but if we assume that it was about 180 meters, then Aristotle's estimate is about twice the currently accepted value. The Greeks also had a third argument in favor of the round shape of the Earth: how else to explain why, when a ship approaches the shore, first only its sails are shown, and only then the hull?

Aristotle believed that the Earth was motionless, and also believed that the Sun, Moon, planets and stars revolved in circular orbits around the Earth. He was guided by mystical considerations: the Earth, according to Aristotle, is the center of the Universe, and circular motion is the most perfect. In the 2nd century AD, Ptolemy built a comprehensive cosmological model based on this idea. At the center of the Universe was the Earth, surrounded by eight nested rotating spheres, and on these spheres were located the Moon, Sun, stars and the five planets known at that time - Mercury, Venus, Mars, Jupiter and Saturn (Fig. 1.1). Each planet moved relative to its sphere in a small circle - in order to describe the very complex trajectories of these luminaries in the sky. The stars were fixed to the outer sphere, and therefore their relative positions remained unchanged, the configuration rotating in the sky as a single whole. Ideas about what was located outside the outer sphere remained very vague, but it was certainly located outside the part of the Universe accessible to humanity for observation.

Ptolemy's model made it possible to quite accurately predict the position of the luminaries in the sky. But in order to achieve agreement between predictions and observations, Ptolemy had to assume that the distance from the Moon to the Earth at different times could differ by a factor of two. This meant that the apparent size of the Moon sometimes had to be twice as large as usual! Ptolemy was aware of this shortcoming of his system, which nevertheless did not prevent the almost unanimous recognition of his picture of the world. The Christian Church accepted the Ptolemaic system because it found it consistent with Scripture: there was plenty of room for heaven and hell beyond the sphere of the fixed stars.

But in 1514, the Polish priest Nicolaus Copernicus proposed a simpler model. (However, at first, for fear of being accused of heresy by the church, Copernicus disseminated his cosmological ideas anonymously.) Copernicus proposed that the Sun was motionless and located in the center, and the Earth and planets moved around it in circular orbits. It took almost a century for this idea to be taken seriously. Two astronomers, the German Johannes Kepler and the Italian Galileo Galilei, were among the first to publicly speak out in favor of the Copernican theory, despite the fact that the trajectories of celestial bodies predicted by this theory did not coincide exactly with those observed. The final blow to the world system of Aristotle and Ptolemy was dealt by the events of 1609 - then Galileo began observing the night sky through the newly invented telescope 2
The telescope as a spotting scope was first invented by the Dutch spectacle maker Johann Lippershey in 1608, but Galileo was the first to point a telescope at the sky in 1609 and use it for astronomical observations. – Note translation

Looking at the planet Jupiter, Galileo discovered several small moons orbiting around it. It followed that not all celestial bodies revolve around the Earth, as Aristotle and Ptolemy believed. (One could, of course, continue to consider the Earth stationary and located at the center of the Universe, believing that the satellites of Jupiter move around the Earth in extremely intricate trajectories so that it is similar to their revolution around Jupiter. But still, Copernicus’ theory was much simpler.) Approximately at the same time, Kepler clarified the Copernican theory, suggesting that the planets do not move in circular orbits, but in elliptical (i.e., elongated) orbits, thanks to which it was possible to achieve agreement between the predictions of the theory and observations.

True, Kepler considered ellipses only as a mathematical trick, and a very odious one at that, because ellipses are less perfect figures than circles. Kepler discovered, almost by accident, that elliptical orbits described observations well, but he could not reconcile the assumption of elliptical orbits with his idea of ​​​​magnetic forces as the cause of the motion of planets around the Sun. The reason for the motion of the planets around the Sun was revealed much later, in 1687, by Sir Isaac Newton in his treatise “Mathematical Principles of Natural Philosophy” - perhaps the most important work on physics ever published. In this work, Newton not only put forward a theory describing the movement of bodies in space and time, but also developed a complex mathematical apparatus necessary to describe this movement. In addition, Newton formulated the law of universal gravitation, according to which every body in the Universe is attracted to any other body with a force, which is greater, the greater the mass of the bodies and the smaller the distance between interacting bodies. This is the same force that causes objects to fall to the ground. (The story that Newton's idea of ​​the law of universal gravitation was inspired by an apple falling on his head is most likely just a fiction. Newton only said that the idea came to him when he was "in a contemplative mood" and was "under the impression from the fall of an apple.”) Newton showed that, according to the law he formulated, under the influence of gravity, the Moon should move in an elliptical orbit around the Earth, and the Earth and the planets should move in elliptical orbits around the Sun.

The Copernican model eliminated the need for Ptolemaic spheres, and with them the assumption that the Universe had some kind of natural external boundary. Since the “fixed” stars did not show any movement other than the general daily movement of the sky caused by the rotation of the Earth around its axis, it was natural to assume that these were the same bodies as our Sun, only located much further away.

Newton realized that according to his theory of gravity, stars must attract each other and therefore, apparently, cannot remain motionless. Why didn’t they get closer and accumulate in one place? In a letter to another prominent thinker of his time, Richard Bentley, written in 1691, Newton argued that they would converge and cluster only if the number of stars concentrated in a limited region of space was finite. And if the number of stars is infinite and they are distributed more or less evenly in infinite space, then this will not happen due to the absence of any obvious central point into which the stars could “fall”.

This is one of those pitfalls that occur when thinking about infinity. In an infinite Universe, any point can be considered its center, because on each side of it there is an infinite number of stars. The correct approach (which came much later) is to solve the problem in the finite case where stars fall on each other, and study how the result changes when adding stars to the configuration that are located outside the region under consideration and are distributed more or less evenly. According to Newton's law, on average, the additional stars in the aggregate should have no effect on the original stars, and therefore these stars of the original configuration should still fall rapidly into one another. So no matter how many stars you add, they will still fall on top of each other. Now we know that it is impossible to obtain an infinite stationary model of the Universe in which the force of gravity is exclusively “attractive” in nature.

It says a lot about the intellectual atmosphere before the beginning of the 20th century that no one then thought of a scenario according to which the Universe could contract or expand. The generally accepted concept of the Universe was either that it had always existed in an unchanged form, or that it had been created at some point in the past - in the form in which we observe it now. This could, in part, be a consequence of the fact that people tend to believe in eternal truths. It is worth remembering at least that the greatest comfort comes from the thought that although we all grow old and die, the Universe is eternal and unchanging.

Even scientists who understood that, according to Newton's theory of gravity, the Universe could not be static, did not dare to suggest that it could expand. Instead, they tried to adjust the theory so that the gravitational force becomes repulsive over very large distances. This assumption did not significantly change the predicted movements of the planets, but allowed an infinite number of stars to remain in a state of equilibrium: the attractive forces from nearby stars were balanced by the repulsive forces from more distant stars. Now it is believed that such an equilibrium state must be unstable: as soon as the stars in any region get a little closer to each other, their mutual attraction will intensify and exceed the repulsive forces, as a result of which the stars will continue to fall on each other. On the other hand, if the stars are only slightly further away from each other, the repulsive forces will prevail over the attractive forces and the stars will fly apart.

Another objection to the concept of an infinite static universe is usually associated with the name of the German philosopher Heinrich Olbers, who published his reasoning on this matter in 1823. In fact, many of Newton's contemporaries drew attention to this problem, and Olbers's paper was by no means the first to present strong arguments against such a concept. However, it was the first to receive widespread recognition. The fact is that in an infinite static Universe, almost any ray of vision should rest on the surface of some star, and therefore the entire sky should glow as brightly as the Sun, even at night. Olbers' counter-argument was that the light from distant stars must be attenuated by absorption by matter between us and those stars. But then this substance would heat up and glow as brightly as the stars themselves. The only way to avoid the conclusion that the brightness of the entire sky is comparable to the brightness of the Sun is to assume that the stars did not shine forever, but “lit up” some specific time ago. In this case, the absorbing substance would not have time to heat up or the light of distant stars would not have time to reach us. Thus, we come to the question of the reason why the stars lit up.

Of course, people discussed the origin of the universe long before this. In many early cosmological ideas, as well as in Jewish, Christian and Muslim pictures of the world, the Universe arose at a certain and not very distant time in the past. One of the arguments in favor of such a beginning was the feeling of the need for some kind of first cause that would explain the existence of the Universe. (Within the Universe itself, any event that occurs in it is explained as a consequence of another, earlier event; the existence of the Universe itself can be explained in this way only by supposing that it had some kind of beginning.) Another argument was expressed by Aurelius Augustine, or St. Augustine, in the work “On the City of God.” He noted that civilization is developing and that we remember who committed this or that act or invented this or that mechanism. Consequently, man, and perhaps the Universe, could not have existed for a very long time. St. Augustine believed, in accordance with the Book of Genesis, that the Universe was created approximately 5000 years before the birth of Christ. (Interestingly, this is close to the end of the last Ice Age - around 10,000 BC - which archaeologists consider the beginning of civilization.)

Aristotle, as well as most ancient Greek philosophers, on the contrary, did not like the idea of ​​​​the creation of the world, because it came from divine intervention. They believed that the human race and the world have always existed and will exist forever. The thinkers of antiquity also comprehended the above-mentioned argument about the progress of civilization and countered: they stated that the human race periodically returned to the stage of the beginning of civilization under the influence of floods and other natural disasters.

Questions about whether the Universe had a beginning in time and whether it is limited in space were also raised by the philosopher Immanuel Kant in his monumental (though very difficult to understand) work “Critique of Pure Reason,” published in 1781. Kant called these questions the antinomies (that is, contradictions) of pure reason because he felt that there were equally compelling arguments for both the thesis - that is, that the Universe had a beginning - and the antithesis, that is, that the Universe has always existed . To prove his thesis, Kant cites the following reasoning: if the Universe had no beginning, then any event should have been preceded by an infinite time, which, according to the philosopher, is absurd. In favor of the antithesis, the consideration was put forward that if the Universe had a beginning, then an infinite amount of time must have passed before it, and it is not clear why the Universe arose at any specific moment in time. In essence, Kant's justifications for thesis and antithesis are almost identical. In both cases, the reasoning is based on the philosopher's implicit assumption that time continues indefinitely into the past, regardless of whether the Universe has always existed. As we will see, the concept of time has no meaning until the birth of the Universe. St. Augustine was the first to note this. He was asked, “What did God do before he created the world?” and Augustine did not argue that God was preparing hell for those who asked such questions. Instead, he postulated that time is a property of God's created world and that before the beginning of the universe, time did not exist.

When most people considered the universe as a whole to be static and unchanging, the question of whether it had a beginning was more a matter of metaphysics or theology. The observed picture of the world could equally well be explained both within the framework of the theory that the Universe has always existed, and on the basis of the assumption that it was set in motion at some specific time, but in such a way that the appearance remains that it exists forever. But in 1929, Edwin Hubble made a fundamental discovery: he noticed that distant galaxies, no matter where they are in the sky, are always moving away from us at high speeds [proportional to their distance] 3
Here and below, the translator's comments clarifying the author's text are placed in square brackets. – Note ed.

In other words, the Universe is expanding. This means that in the past, objects in the Universe were closer to each other than they are now. And it seems that at some point in time - somewhere 10-20 billion years ago - everything that is in the Universe was concentrated in one place, and therefore the density of the Universe was infinite. This discovery brought the question of the beginning of the Universe into the realm of science.

A BRIEF HISTORY OF TIME

The publishing house expresses gratitude to the literary agencies Writers House LLC (USA) and Synopsis Literary Agency (Russia) for their assistance in acquiring rights.

© Stephen Hawking 1988.

© N.Ya. Smorodinskaya, per. from English, 2017

© Y.A. Smorodinsky, afterword, 2017

© AST Publishing House LLC, 2017

* * *

Dedicated to Jane

Gratitude

I decided to try to write a popular book about space and time after giving the Loeb Lectures at Harvard in 1982. At that time there were already quite a few books devoted to the early Universe and black holes, both very good, for example Steven Weinberg’s book “The First Three Minutes,” and very bad, which there is no need to name here. But it seemed to me that none of them actually addressed the questions that prompted me to study cosmology and quantum theory: where did the universe come from? How and why did it arise? Will it come to an end, and if it does, how? These questions interest us all. But modern science is full of mathematics, and only a few specialists know it enough to understand all this. However, the basic ideas about the birth and further fate of the Universe can be presented without the help of mathematics in such a way that they will become understandable even to people who have not received special education. This is what I tried to do in my book. How much I succeeded in this is for the reader to judge.

I was told that every formula included in the book would cut the number of buyers in half. Then I decided to do without formulas altogether. True, in the end I still wrote one equation - the famous Einstein equation E=mc². I hope it doesn't scare off half of my potential readers.

Apart from my illness - amyotrophic lateral sclerosis - then in almost everything else I was lucky. The help and support provided by my wife Jane and children Robert, Lucy and Timothy enabled me to lead a relatively normal life and achieve success at work. I was also lucky that I chose theoretical physics, because it all fits in my head. Therefore, my physical weakness did not become a serious obstacle. My colleagues, without exception, have always provided me with maximum assistance.

During the first, “classic” stage of my work, my closest colleagues and assistants were Roger Penrose, Robert Gerok, Brandon Carter and George Ellis. I am grateful to them for their help and cooperation. This phase culminated in the publication of the book “Large-Scale Structure of Spacetime,” which Ellis and I wrote in 1973. I would not advise readers to turn to it for more information: it is overloaded with formulas and difficult to read. I hope that since then I have learned to write more accessiblely.

During the second, "quantum" phase of my work, which began in 1974, I worked primarily with Gary Gibbons, Don Page, and Jim Hartle. I owe a lot to them, as well as to my graduate students, who provided me with enormous help in both the “physical” and “theoretical” sense of the word. The need to keep up with graduate students was an extremely important motivator and, I think, kept me from getting stuck in a mire.

Brian Witt, one of my students, helped me a lot in writing this book. In 1985, after sketching out the first rough outline of the book, I fell ill with pneumonia. And then the operation, and after the tracheotomy I stopped speaking, essentially losing the ability to communicate. I thought I wouldn't be able to finish the book. But Brian not only helped me revise it, he also taught me how to use the Living Center communication computer program, which was given to me by Walt Waltosh of Words Plus, Inc., Sunnyvale, California. With its help, I can write books and articles, and also talk to people through a speech synthesizer given to me by another Sunnyvale company, Speech Plus. David Mason installed this synthesizer and a small personal computer on my wheelchair. This system changed everything: it became even easier for me to communicate than before I lost my voice.

I am grateful to many who have read early versions of the book for suggestions on how it could be improved. Thus, Peter Gazzardi, editor of Bantam Books, sent me letter after letter with comments and questions regarding points that, in his opinion, were poorly explained. Admittedly, I was quite annoyed when I received a huge list of recommended fixes, but Gazzardi was absolutely right. I'm sure the book was made much better by Gazzardi rubbing my nose in the mistakes.

My deepest gratitude goes to my assistants Colin Williams, David Thomas and Raymond Laflamme, my secretaries Judy Fella, Ann Ralph, Cheryl Billington and Sue Macy, and my nurses.

I could not have achieved anything if all the costs of scientific research and necessary medical care had not been borne by Gonville and Caius College, the Science and Technology Research Council and the Leverhulme, MacArthur, Nuffield and Ralph Smith Foundations. I am very grateful to all of them.

October 20, 1987

Stephen Hawking

Chapter first
Our idea of ​​the Universe

Once a famous scientist (they say it was Bertrand Russell) gave a public lecture on astronomy. He told how the Earth revolves around the Sun, and the Sun, in turn, revolves around the center of a huge cluster of stars called our Galaxy. As the lecture came to an end, a little old lady stood up from the last row and said, “Everything you told us is nonsense. In fact, our world is a flat plate that sits on the back of a giant turtle.” Smiling indulgently, the scientist asked: “What does the turtle support?” “You are very smart, young man,” replied the old lady. “A turtle is on another turtle, that one is also on a turtle, and so on, and so on.”

The idea of ​​the Universe as an endless tower of turtles will seem funny to most of us, but why do we think we know better? What do we know about the Universe and how did we know it? Where did the Universe come from and what will happen to it? Did the Universe have a beginning, and if so, what happened? before the beginning? What is the essence of time? Will it ever end? The achievements of physics in recent years, which we to some extent owe to fantastic new technology, allow us to finally obtain answers to at least some of these questions that have long been facing us. As time passes, these answers may be as certain as the fact that the Earth revolves around the Sun, and perhaps as ridiculous as a tower of turtles. Only time (whatever that is) will decide.

Back in 340 BC. e. The Greek philosopher Aristotle, in his book “On the Heavens,” gave two compelling arguments in favor of the fact that the Earth is not flat, like a plate, but round, like a ball. First, Aristotle guessed that lunar eclipses occur when the Earth is between the Moon and the Sun. The Earth always casts a round shadow on the Moon, and this can only happen if the Earth is spherical. If the Earth were a flat disk, its shadow would have the shape of an elongated ellipse - unless an eclipse always occurs at the exact moment when the Sun is exactly on the axis of the disk. Secondly, from the experience of their sea voyages, the Greeks knew that in the southern regions the North Star is lower in the sky than in the northern ones. (Since the North Star is above the North Pole, it will be directly above the head of an observer standing at the North Pole, and to a person at the equator it will seem that it is on the horizon.) Knowing the difference in the apparent position of the North Star in Egypt and Greece, Aristotle was even able to calculate that the length of the equator is 400,000 stadia. What the stade was equal to is not known exactly, but it was approximately 200 meters, and therefore Aristotle’s estimate is about 2 times the value now accepted. The Greeks also had a third argument in favor of the spherical shape of the Earth: if the Earth is not round, then why do we first see the sails of a ship rising above the horizon, and only then the ship itself?

Aristotle believed that the Earth is motionless, and the Sun, Moon, planets and stars revolve around it in circular orbits. In accordance with his mystical views, he considered the Earth to be the center of the Universe, and circular motion to be the most perfect. In the 2nd century, Ptolemy developed Aristotle's idea into a complete cosmological model. The Earth stands in the center, surrounded by eight spheres bearing the Moon, the Sun and the five then known planets: Mercury, Venus, Mars, Jupiter and Saturn (Fig. 1.1). The planets themselves, Ptolemy believed, moved in smaller circles connected to the corresponding spheres. This explained the very complex path that we see the planets take. On the very last sphere are the fixed stars, which, remaining in the same position relative to each other, move across the sky all together as a single whole. What lay beyond the last sphere was not explained, but in any case it was no longer part of the Universe that humanity observes.

Rice. 1.1

Ptolemy's model made it possible to predict quite well the position of celestial bodies in the sky, but for an accurate prediction he had to accept that in some places the Moon's trajectory passes 2 times closer to the Earth than in others. This means that in one position the Moon should appear 2 times larger than in another! Ptolemy was aware of this shortcoming, but nevertheless his theory was recognized, although not everywhere. The Christian Church accepted the Ptolemaic model of the Universe as not contradicting the Bible: this model was good because it left a lot of space for hell and heaven outside the sphere of the fixed stars. However, in 1514, the Polish priest Nicolaus Copernicus proposed an even simpler model. (At first, perhaps fearing that the Church would declare him a heretic, Copernicus promoted his model anonymously.) His idea was that the Sun stood motionless in the center, and the Earth and other planets revolved around it in circular orbits. Almost a century passed before Copernicus' idea was taken seriously. Two astronomers - the German Johannes Kepler and the Italian Galileo Galilei - came out in support of Copernicus' theory, despite the fact that the orbits predicted by Copernicus did not exactly match those observed. The Aristotle-Ptolemy theory was found untenable in 1609, when Galileo began observing the night sky using a newly invented telescope. By pointing his telescope at the planet Jupiter, Galileo discovered several small satellites, or moons, that orbit Jupiter. This meant that not all celestial bodies must necessarily revolve directly around the Earth, as Aristotle and Ptolemy believed. (Of course, one could still assume that the Earth rests at the center of the Universe, and the moons of Jupiter move along a very complex path around the Earth, so that they only appear to orbit Jupiter. However, Copernicus’ theory was much simpler.) At the same time At the time, Johannes Kepler modified Copernicus' theory based on the assumption that planets move not in circles, but in ellipses (an ellipse is an elongated circle). Finally, now the predictions coincided with the results of observations.

As for Kepler, his elliptical orbits were an artificial (ad hoc) hypothesis, and, moreover, an “ungraceful” one, since an ellipse is a much less perfect figure than a circle. Having discovered almost by accident that elliptical orbits were in good agreement with observations, Kepler was never able to reconcile this fact with his idea that the planets revolve around the Sun under the influence of magnetic forces. The explanation came much later, in 1687, when Isaac Newton published his book “Mathematical Principles of Natural Philosophy.” In it, Newton not only put forward a theory of the movement of material bodies in time and space, but also developed complex mathematical methods necessary to analyze the movement of celestial bodies. In addition, Newton postulated the law of universal gravitation, according to which every body in the Universe is attracted to any other body with the greater force, the greater the mass of these bodies and the smaller the distance between them. This is the same force that makes bodies fall to the ground. (The story that Newton was inspired by an apple falling on his head is almost certainly unreliable. Newton himself said only that the idea of ​​gravity occurred to him while he was sitting in a “contemplative mood” and “the occasion was the fall of an apple ".) Newton further showed that, according to his law, the Moon, under the influence of gravitational forces, moves in an elliptical orbit around the Earth, and the Earth and the planets rotate in elliptical orbits around the Sun.

The Copernican model helped get rid of the Ptolemaic celestial spheres, and at the same time the idea that the Universe had some kind of natural boundary. Since the “fixed stars” do not change their position in the sky, except for their circular motion associated with the rotation of the Earth around its axis, it was natural to assume that the fixed stars are objects similar to our Sun, only much more distant.

Newton understood that, according to his theory of gravity, stars should be attracted to each other and therefore, it would seem, cannot remain completely motionless. Shouldn't they fall on top of each other, getting closer at some point? In 1691, in a letter to Richard Bentley, a leading thinker of the time, Newton said that this would indeed happen if we had only a finite number of stars in a finite region of space. But, Newton reasoned, if the number of stars is infinite and they are more or less evenly distributed over infinite space, then this will never happen, since there is no central point where they would need to fall.

These arguments are an example of how easy it is to get into trouble when talking about infinity. In an infinite Universe, any point can be considered the center, since on both sides of it the number of stars is infinite. It was only much later that they realized that a more correct approach was to take a finite system in which all the stars fall on each other, tending to the center, and see what changes would happen if we added more and more stars, distributed approximately evenly outside the region under consideration. According to Newton's law, additional stars, on average, will not affect the original ones in any way, that is, the stars will fall at the same speed into the center of the selected area. No matter how many stars we add, they will always tend to the center. Nowadays, it is known that an infinite static model of the Universe is impossible if gravitational forces always remain forces of mutual attraction.

It’s interesting what the general state of scientific thought was like before the beginning of the twentieth century: it never occurred to anyone that the Universe could expand or contract. Everyone believed that the Universe either always existed in an unchanged state, or was created at some point in time in the past approximately as it is now. This may be partly explained by the tendency of people to believe in eternal truths, and also by the special attraction of the idea that, although they themselves grow old and die, the Universe will remain eternal and unchanging.

Even those scientists who realized that Newton's theory of gravity made a static Universe impossible did not think of the expanding Universe hypothesis. They tried to modify the theory by making the gravitational force repulsive over very large distances. This practically did not change the predicted motion of the planets, but it allowed the infinite distribution of stars to remain in equilibrium, since the attraction of nearby stars was compensated by repulsion from distant ones. But now we believe that such an equilibrium would be unstable. In fact, if in some area the stars get a little closer, then the attractive forces between them will increase and become stronger than the repulsive forces, so that the stars will continue to come closer. If the distance between the stars increases slightly, then the repulsive forces will outweigh and the distance will increase.

Another objection to the model of an infinite static universe is usually attributed to the German philosopher Heinrich Olbers, who published a work on this model in 1823. In fact, many of Newton's contemporaries were working on the same problem, and Albers's paper was not even the first to raise serious objections. She was the first to be widely quoted. The objection is this: in an infinite static Universe, any ray of vision must rest on some star. But then the sky, even at night, should glow brightly, like the Sun. Olbers's counter-argument was that light coming to us from distant stars should be attenuated by absorption in matter in its path. But in this case, this substance itself should heat up and glow brightly, like stars. The only way to avoid the conclusion that the night sky glows brightly, like the Sun, is to assume that the stars did not always shine, but lit up at some specific point in time in the past. Then the absorbing substance may not have had time to warm up yet, or the light of distant stars has not yet reached us. But the question arises: why did the stars light up?

Of course, the problem of the origin of the Universe has occupied the minds of people for a very long time. According to a number of early cosmogonies and Judeo-Christian-Muslim myths, our Universe arose at some specific and not very distant point in time in the past. One of the reasons for such beliefs was the need to find the “first cause” of the existence of the Universe. Any event in the Universe is explained by indicating its cause, that is, another event that happened earlier; such an explanation of the existence of the Universe itself is possible only if it had a beginning. Another basis was put forward by Augustine the Blessed in his essay “On the City of God.” He pointed out that civilization is progressing, and we remember who committed this or that act and who invented what. Therefore, humanity, and therefore probably the Universe, is unlikely to exist for very long. Augustine the Blessed considered the acceptable date for the creation of the Universe, corresponding to the book of Genesis: approximately 5000 BC. e. (Interestingly, this date is not too far from the end of the last ice age - 10,000 BC, which archaeologists consider the beginning of civilization.)

Aristotle and most other Greek philosophers did not like the idea of ​​the creation of the Universe, since it was associated with divine intervention. Therefore, they believed that people and the world around them existed and would exist forever. Scientists of antiquity considered the argument regarding the progress of civilization and decided that floods and other cataclysms periodically occurred in the world, which all the time returned humanity to the starting point of civilization.

The questions of whether the Universe arose at some initial point in time and whether it is limited in space were later examined very closely by the philosopher Immanuel Kant in his monumental (and very obscure) work “Critique of Pure Reason,” which was published in 1781. He called these questions antinomies (i.e., contradictions) of pure reason, because he saw that it was equally impossible to prove or disprove both the thesis about the necessity of the beginning of the Universe and the antithesis about its eternal existence. Kant's thesis was argued by the fact that if the Universe had no beginning, then every event would be preceded by an infinite period of time, and Kant considered this absurd. In support of the antithesis, Kant said that if the Universe had a beginning, then it would have been preceded by an infinite period of time, and then the question is, why did the Universe suddenly arise at one point in time and not at another? In fact, Kant's arguments are virtually the same for both thesis and antithesis. It proceeds from the tacit assumption that time is infinite in the past, regardless of whether the universe existed or did not exist forever. As we will see below, before the emergence of the Universe, the concept of time is meaningless. This was first pointed out by St. Augustine. When asked what God was doing before he created the universe, Augustine never answered that God was preparing hell for those who asked such questions. No, he said that time is an integral property of the Universe created by God and therefore there was no time before the emergence of the Universe.

When most people believed in a static and unchanging universe, the question of whether it had a beginning or not was essentially a matter of metaphysics and theology. All observable phenomena could be explained either by a theory in which the universe existed forever, or by a theory in which the universe was created at some specific point in time in such a way that everything looked as if it had existed forever. But in 1929, Edwin Hubble made an epochal discovery: it turned out that no matter what part of the sky one observes, all distant galaxies are rapidly moving away from us. In other words, the Universe is expanding. This means that in earlier times all objects were closer to each other than they are now. This means that there was apparently a time, about ten or twenty thousand million years ago, when they were all in one place, so that the density of the Universe was infinitely large. Hubble's discovery brought the question of how the Universe began into the realm of science.

Hubble's observations suggested that there was a time, the so-called Big Bang, when the Universe was infinitely small and infinitely dense. Under such conditions, all the laws of science become meaningless and do not allow us to predict the future. If in even earlier times any events took place, they still could not in any way affect what is happening now. Due to the lack of observable consequences, they can simply be neglected. The Big Bang can be considered the beginning of time in the sense that earlier times would simply not be defined. Let us emphasize that such a starting point for time is very different from everything that was proposed before Hubble. The beginning of time in an unchanging Universe is something that must be determined by something existing outside the Universe; There is no physical necessity for the beginning of the Universe. The creation of the Universe by God can be attributed to any point in time in the past. If the Universe is expanding, then there may be physical reasons for it to have a beginning. You can still imagine that it was God who created the Universe - at the moment of the Big Bang or even later (but as if the Big Bang had happened). However, it would be absurd to say that the Universe came into existence before the Big Bang. The idea of ​​an expanding Universe does not exclude the creator, but it does impose restrictions on the possible date of his work!

In order to be able to talk about the essence of the Universe and whether it had a beginning and whether there will be an end, you need to have a good understanding of what a scientific theory is in general. I will adhere to the simplest point of view: a theory is a theoretical model of the Universe or some part of it, supplemented by a set of rules connecting theoretical quantities with our observations. This model exists only in our heads and has no other reality (no matter what meaning we put into this word). A theory is considered good if it satisfies two requirements: first, it must accurately describe a wide class of observations within a model containing only a few arbitrary elements, and second, the theory must make well-defined predictions about the results of future observations. For example, Aristotle's theory that everything was made up of four elements—earth, air, fire, and water—was simple enough to be called a theory, but it did not make any definite predictions. Newton's theory of gravitation proceeded from an even simpler model, in which bodies are attracted to each other with a force proportional to a certain quantity called their mass, and inversely proportional to the square of the distance between them. But Newton's theory very accurately predicts the movement of the Sun, Moon and planets.

Any physical theory is always temporary in the sense that it is just a hypothesis that cannot be proven. No matter how many times the theory agrees with experimental data, one cannot be sure that the next time the experiment will not contradict the theory. At the same time, any theory can be refuted by referring to a single observation that does not agree with its predictions. As the philosopher Karl Popper, a specialist in the field of philosophy of science, pointed out, a necessary feature of a good theory is that it makes predictions that can, in principle, be experimentally falsified. Whenever new experiments confirm the predictions of a theory, the theory demonstrates its vitality and our faith in it grows stronger. But if even one new observation does not agree with the theory, we have to either abandon it or redo it. This is at least the logic, although, of course, you always have the right to doubt the competence of the one who carried out the observations.

In practice, it often turns out that a new theory is actually an extension of the previous one. For example, extremely precise observations of the planet Mercury have revealed small discrepancies between its motion and the predictions of Newton's theory of gravity. According to Einstein's general theory of relativity, Mercury should move slightly differently than Newton's theory. The fact that Einstein's predictions coincided with observational results, but Newton's predictions did not coincide, became one of the decisive confirmations of the new theory. True, in practice we still use Newton's theory, since in the cases we usually encounter, its predictions differ very little from the predictions of general relativity. (Newton's theory also has the great advantage that it is much easier to work with than Einstein's theory.)

The ultimate goal of science is to create a unified theory that would describe the entire Universe. When solving this problem, most scientists divide it into two parts. The first part is the laws that give us the opportunity to know how the Universe changes over time. (Knowing what the Universe looks like at one point in time, we can use these laws to find out what will happen to it at any later point in time.) The second part is the problem of the initial state of the Universe. Some believe that science should deal only with the first part, and consider the question of what was in the beginning to be a matter of metaphysics and religion. Proponents of this view say that since God is omnipotent, it was his will to “run” the universe as he pleased. If they are right, then God had the opportunity to make the universe develop completely randomly. God, apparently, preferred that it develop very regularly, according to certain laws. But then it is just as logical to assume that there are also laws governing the initial state of the Universe.

It turns out that it is very difficult to immediately create a theory that would describe the entire Universe. Instead, we divide the problem into parts and build partial theories. Each of them describes one limited class of observations and makes predictions about it, neglecting the influence of all other quantities or representing the latter as simple sets of numbers. It is possible that this approach is completely wrong. If everything in the universe fundamentally depends on everything else, then it is possible that by studying parts of a problem in isolation, one cannot get closer to a complete solution. Nevertheless, in the past our progress has been this way. A classic example is again Newton's theory of gravity, according to which the gravitational force acting between two bodies depends only on one characteristic of each body, namely its mass, but does not depend on what substance the bodies are made of. Consequently, to calculate the orbits in which the Sun and planets move, a theory of their structure and composition is not needed.

Now there are two main partial theories to describe the Universe: general relativity and quantum mechanics. Both of them are the result of enormous intellectual efforts of scientists in the first half of the 20th century. General relativity describes the gravitational interaction and large-scale structure of the Universe, that is, structure on a scale from a few kilometers to a million million million million (one followed by twenty-four zeros) kilometers, or up to the size of the observable part of the Universe. Quantum mechanics deals with phenomena on extremely small scales, such as one millionth of one millionth of a centimeter. And these two theories, unfortunately, are incompatible - they cannot be correct at the same time. One of the main areas of research in modern physics and the main theme of this book is the search for a new theory that would combine the two previous ones into one - the quantum theory of gravity. There is no such theory yet, and it may still have to wait a long time, but we already know many of the properties that it should have. In the following chapters you will see that we already know a lot about what predictions should follow from the quantum theory of gravity.

If you believe that the Universe does not develop in an arbitrary manner, but obeys certain laws, then in the end you will have to combine all the partial theories into a single complete one that will describe everything in the Universe. True, there is one fundamental paradox in the search for such a unified theory. Everything said above about scientific theories assumes that we are intelligent beings, we can make any observations in the Universe and draw logical conclusions based on these observations. In such a scheme, it is natural to assume that, in principle, we could come even closer to understanding the laws that govern our Universe. But if a unified theory really exists, then it should probably also somehow influence our actions. And then the theory itself should determine the result of our search for it! Why should she predetermine in advance that we will draw the correct conclusions from observations? Why shouldn't she just as easily lead us to the wrong conclusions? Or none at all?