Stephen Hawking
A BRIEF HISTORY OF TIME.
From the big bang to black holes
Thanks
The book is dedicated to Jane
I decided to try writing a popular book on space and time after I gave the Loeb Lectures at Harvard in 1982. There were already quite a few books on the early universe and black holes, both very good, such as Steven Weinberg's The First Three Minutes, and very bad, which need not be mentioned here. But it seemed to me that none of them actually touched on the questions that prompted me to study cosmology and quantum theory: where did the universe come from? how and why did it come about? Will it end, and if so, how? These questions are of interest to all of us. But modern science is very saturated with mathematics, and only a few specialists know the latter enough to understand it. However, the basic ideas about the birth and further fate of the Universe can be stated without the help of mathematics in such a way that they become understandable even to people who have not received a scientific education. This is what I tried to do in my book. It is up to the reader to judge how well I have succeeded.
I was told that each formula included in the book would halve the number of buyers. Then I decided to do without formulas at all. True, in the end I did write one equation - the famous Einstein equation E = mc ^ 2. I hope it doesn't scare away half of my potential readers.
Apart from the fact that I got amyotrophic lateral sclerosis, I was lucky in almost everything else. The help and support I received from my wife, Jane, and children, Robert, Lucy, and Timothy, enabled me to lead a fairly normal life and be successful 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 minus. My scientific colleagues, without exception, have always provided me with maximum assistance.
At the first, “classic” stage of my work, my closest assistants and collaborators were Roger Penrose, Robert Gerok, Brandon Carter and George Ellis. I am grateful to them for their help and for their joint work. This stage ended with the publication of the book "Large-scale structure of space-time", which Ellis and I wrote in 1973 (Hawking S., Ellis J. Large-scale structure of space-time. M .: Mir, 1976).
During the second, "quantum" phase of my work, which began in 1974, I mainly worked 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 great help both in the “physical” and in the “theoretical” sense of the word. The need to keep up with graduate students was an extremely important incentive and, I think, kept me from getting stuck in a swamp.
Brian Witt, one of my students, helped me a lot with this book. In 1985, having sketched out the first, rough outline of the book, I fell ill with pneumonia. I had to undergo an operation, and after the tracheotomy, I stopped talking, and thus almost lost the ability to communicate. I thought I wouldn't be able to finish the book. But Brian not only helped me revise it, but also taught me how to use the Living Center communication computer program that Walt Waltosh of Words Plus, Inc., Sunnyvale, California, gave me. With it, I can write books and articles, as well as talk to people through a speech synthesizer donated to me by another Sunnyvale firm, 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.
To many of those who have read the preliminary versions of the book, I am grateful for advice on how it could be improved. For example, Peter Gazzardi, my editor at Bantam Books, sent me letter after letter with comments and questions about passages he thought were poorly explained. Frankly, I was very annoyed when I received a huge list of recommended fixes, but Gazzardi was absolutely right. I'm sure the book got better because Gazzardi poked my nose into mistakes.
I express my deep gratitude to my assistants Colin Williams, David Thomas and Raymond Laflamm, my secretaries Judy Felle, Ann Ralph, Cheryl Billington and Sue Macy and my nurses. I could not have achieved anything if Gonville and Cayus College, the Council for Scientific and Technical Research, and the Leverhulme, MacArthur, Nuffield, and Ralph Smith Foundations had not assumed all the costs of scientific research and necessary medical care. To all of them I am very grateful.
Foreword
We live, understanding almost nothing in the structure of the world. We don’t think about what mechanism generates sunlight that ensures our existence, we don’t think about gravity, which keeps us on Earth, preventing it from dropping us into space. We are not interested in the atoms of which we are composed and on the stability of which we ourselves essentially depend. With the exception of children (who still know too little not to ask such serious questions), few people puzzle over why nature is the way it is, where did the cosmos come from and whether it has always existed? can time not one day turn back, so that the effect precedes the cause? Is there an insurmountable limit to human knowledge? There are even children (I met them) who want to know what a black hole looks like, what is the smallest particle of matter? Why do we remember the past and not the future? if there really was chaos before, how did it happen that now a visible order has been established? and why does the universe exist at all?
In our society, it is common for parents and teachers to respond to these questions by shrugging their shoulders or calling for help from vaguely remembered references to religious legends. Some do not like such topics because they vividly reveal the narrowness of human understanding.
But the development of philosophy and the natural sciences moved forward mainly due to such questions. More and more adults are showing interest in them, and the answers are sometimes completely unexpected for them. Differing in scale from both atoms and stars, we expand the horizons of research to cover both very small and very large objects.
In the spring of 1974, about two years before the Viking spacecraft reached the surface of Mars, I was in England at a conference organized by the Royal Society of London on the possibility of searching for extraterrestrial civilizations. During the coffee break, I noticed a much more crowded meeting in the next room, and out of curiosity I entered it. So I became a witness to a long-standing ritual - the admission of new members to the Royal Society, which is one of the oldest associations of scientists on the planet. Ahead, a young man sitting in a wheelchair was writing his name very slowly in a book whose previous pages bore the signature of Isaac Newton. When he finally finished signing, the audience burst into applause. Stephen Hawking was already a legend then.
Hawking now holds the chair of mathematics at the University of Cambridge, once held by Newton and later by P. A. M. Dirac, two famous researchers who studied one the largest and the other the smallest. Hawking is their worthy successor. This first popular book by Hockipg contains a lot of useful information for a wide audience. The book is interesting not only for the breadth of its content, it allows you to see how the thought of its author works. You will find in it clear revelations about the limits of physics, astronomy, cosmology and courage.
But it's also a book about God... or maybe about the absence of God. The word "God" often appears on its pages. Hawking sets out to find the answer to Einstein's famous question about whether God had any choice when he created the universe. Hawking is trying, as he writes, to unravel the plan of God. All the more surprising is the conclusion (at least temporarily) to which these
Mastered Stephen Hawking's book "The Briefest History of Time". The author himself became familiar to many - this is the same brilliant physicist, chained to a wheelchair.
The book is interesting, well written and accessible. What especially struck the imagination in my summary:
1) If you draw a straight line between two points on a geographical map with a ruler, then this straight line will not be the shortest distance between the two points. The shortest will be a curve in the form of an arch, the radius of which is equal to the radius of the Earth.
2) In the presence of matter, four-dimensional space-time is distorted, causing curvature of the trajectories of bodies in three-dimensional space. Although it is difficult to depict, the mass of the Sun warps spacetime in such a way that the Earth, following the shortest path in four-dimensional space-time, appears to us as moving in a nearly circular orbit in three-dimensional space.
3) The general theory of relativity declares that the course of time is different for observers in different gravitational fields. If one of the twins lives on a mountain top and the other lives by the sea, the first will age faster than the second.
4) If we knew the state of the system at a given moment and knew the laws of development of the system, we could predict the position of the system at any time. So, the Heisenberg Uncertainty Principle generally says that no matter how puffed up we are, we can’t fucking determine the state of the Universe at the present moment. And it has nothing to do with the level of development of science. This is closer to a philosophical principle - in principle, we cannot know the position of any system at any particular moment. We know at any moment either the speed of the particle or its location. Exactly one of the two, but not both values at once.
Therefore, reconcile yourself - any prediction in our Universe is impossible in principle. From a purely philosophical point of view. Any.
5) If we send an electron into the wall, and put two slits in its path for passage, then it will go through both slits at once. Pause for reflection. In general, an electron can be in all possible positions at the same time. For, the creature is so small, it is not only a particle, but when it wants to, it is also a wave. The binding of an electron to specific orbits of an atom is connected precisely with the fact that it is on these orbits that the electron does not interfere with itself, i.e. does not extinguish itself. Once again - an electron, flying from one point to another, flies along all possible trajectories at once. In fact, he is able to be at all points in space at the same time, and only there he is not, where he interferes with himself.
6) Purely theoretically, time travel to the past is possible. The solution of the equations of the theory of relativity shows that yes, this is so. One thing - to travel back in time, you must definitely move faster than the speed of light. And vice versa - movement faster than the speed of light is impossible without simultaneous movement into the past.
Those who know that it is impossible to move faster than the speed of light breathe a sigh of relief. But there is another problem - purely, again, hypothetically, travel faster than the speed of light is also possible. Possible in the case of the existence of wormholes in space-time. And the damn equations show that yes, such holes can exist. And if they can, then they exist somewhere.
7) The newest theory that simply awesome describes the latest discoveries in science and anticipates them - this is string theory. Nothing special, just everything that is predicted by this theory is then confirmed by one-on-one experiments. And it's really stressful. It's annoying, because string theory takes as an assumption one small statement - we do not live in a four-dimensional world, but in a 26-dimensional one. Moreover, 4 dimensions are deployed, and we can move along them, and 22 more are folded into a point. Physicists would happily abandon this theory, but nothing more intelligible in terms of mathematics has yet been invented, and experiments continue to perfectly match the predictions made on the basis of this theory.
In general, it seems to me that our Universe, like that electron, is capable of being in all states simultaneously, with the exception of those states in which it interferes with itself. And now I am simultaneously in Krasnodar and in Moscow and at Alpha Centauri. And at the same time, there is no me at all. But the thought of Enta is clearly worthy of chewing in a separate abstruse philosophical book.
Stephen Hawking
A BRIEF HISTORY OF TIME.
From the big bang to black holes
Thanks
The book is dedicated to Jane
I decided to try writing a popular book on space and time after I gave the Loeb Lectures at Harvard in 1982. There were already quite a few books on the early universe and black holes, both very good, such as Steven Weinberg's The First Three Minutes, and very bad, which need not be mentioned here. But it seemed to me that none of them actually touched on the questions that prompted me to study cosmology and quantum theory: where did the universe come from? how and why did it come about? Will it end, and if so, how? These questions are of interest to all of us. But modern science is very saturated with mathematics, and only a few specialists know the latter enough to understand it. However, the basic ideas about the birth and further fate of the Universe can be stated without the help of mathematics in such a way that they become understandable even to people who have not received a scientific education. This is what I tried to do in my book. It is up to the reader to judge how well I have succeeded.
I was told that each formula included in the book would halve the number of buyers. Then I decided to do without formulas at all. True, in the end I did write one equation - the famous Einstein equation E = mc ^ 2. I hope it doesn't scare away half of my potential readers.
Apart from the fact that I got amyotrophic lateral sclerosis, I was lucky in almost everything else. The help and support I received from my wife, Jane, and children, Robert, Lucy, and Timothy, enabled me to lead a fairly normal life and be successful 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 minus. My scientific colleagues, without exception, have always provided me with maximum assistance.
At the first, “classic” stage of my work, my closest assistants and collaborators were Roger Penrose, Robert Gerok, Brandon Carter and George Ellis. I am grateful to them for their help and for their joint work. This stage ended with the publication of the book "Large-scale structure of space-time", which Ellis and I wrote in 1973 (Hawking S., Ellis J. Large-scale structure of space-time. M .: Mir, 1976).
During the second, "quantum" phase of my work, which began in 1974, I mainly worked 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 great help both in the “physical” and in the “theoretical” sense of the word. The need to keep up with graduate students was an extremely important incentive and, I think, kept me from getting stuck in a swamp.
Brian Witt, one of my students, helped me a lot with this book. In 1985, having sketched out the first, rough outline of the book, I fell ill with pneumonia. I had to undergo an operation, and after the tracheotomy, I stopped talking, and thus almost lost the ability to communicate. I thought I wouldn't be able to finish the book. But Brian not only helped me revise it, but also taught me how to use the Living Center communication computer program that Walt Waltosh of Words Plus, Inc., Sunnyvale, California, gave me. With it, I can write books and articles, as well as talk to people through a speech synthesizer donated to me by another Sunnyvale firm, 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.
To many of those who have read the preliminary versions of the book, I am grateful for advice on how it could be improved. For example, Peter Gazzardi, my editor at Bantam Books, sent me letter after letter with comments and questions about passages he thought were poorly explained. Frankly, I was very annoyed when I received a huge list of recommended fixes, but Gazzardi was absolutely right. I'm sure the book got better because Gazzardi poked my nose into mistakes.
I express my deep gratitude to my assistants Colin Williams, David Thomas and Raymond Laflamm, my secretaries Judy Felle, Ann Ralph, Cheryl Billington and Sue Macy and my nurses. I could not have achieved anything if Gonville and Cayus College, the Council for Scientific and Technical Research, and the Leverhulme, MacArthur, Nuffield, and Ralph Smith Foundations had not assumed all the costs of scientific research and necessary medical care. To all of them I am very grateful.
Foreword
We live, understanding almost nothing in the structure of the world. We don’t think about what mechanism generates sunlight that ensures our existence, we don’t think about gravity, which keeps us on Earth, preventing it from dropping us into space. We are not interested in the atoms of which we are composed and on the stability of which we ourselves essentially depend. With the exception of children (who still know too little not to ask such serious questions), few people puzzle over why nature is the way it is, where did the cosmos come from and whether it has always existed? can time not one day turn back, so that the effect precedes the cause? Is there an insurmountable limit to human knowledge? There are even children (I met them) who want to know what a black hole looks like, what is the smallest particle of matter? Why do we remember the past and not the future? if there really was chaos before, how did it happen that now a visible order has been established? and why does the universe exist at all?
In our society, it is common for parents and teachers to respond to these questions by shrugging their shoulders or calling for help from vaguely remembered references to religious legends. Some do not like such topics because they vividly reveal the narrowness of human understanding.
But the development of philosophy and the natural sciences moved forward mainly due to such questions. More and more adults are showing interest in them, and the answers are sometimes completely unexpected for them. Differing in scale from both atoms and stars, we expand the horizons of research to cover both very small and very large objects.
In the spring of 1974, about two years before the Viking spacecraft reached the surface of Mars, I was in England at a conference organized by the Royal Society of London on the possibility of searching for extraterrestrial civilizations. During the coffee break, I noticed a much more crowded meeting in the next room, and out of curiosity I entered it. So I became a witness to a long-standing ritual - the admission of new members to the Royal Society, which is one of the oldest associations of scientists on the planet. Ahead, a young man sitting in a wheelchair was writing his name very slowly in a book whose previous pages bore the signature of Isaac Newton. When he finally finished signing, the audience burst into applause. Stephen Hawking was already a legend then.
Hawking now holds the chair of mathematics at the University of Cambridge, once held by Newton and later by P. A. M. Dirac, two famous researchers who studied one the largest and the other the smallest. Hawking is their worthy successor. This first popular book by Hockipg contains a lot of useful information for a wide audience. The book is interesting not only for the breadth of its content, it allows you to see how the thought of its author works. You will find in it clear revelations about the limits of physics, astronomy, cosmology and courage.
Stephen Hawking, Leonard Mlodinov
The shortest history of time
Foreword
Only four letters distinguish the title of this book from the title of the one that was first published in 1988. A Brief History of Time remained on the Sunday Times bestseller list for 237 weeks, and every 750th inhabitant of our planet, adult or child, bought it. A remarkable success for a book dealing with the most difficult problems in modern physics. However, these are not only the most difficult, but also the most exciting problems, because they address us to fundamental questions: what do we really know about the Universe, how did we acquire this knowledge, where did the Universe come from and where is it going? These questions formed the main subject of A Brief History of Time and became the focus of this book. A year after the publication of A Brief History of Time, responses began to pour in from readers of all ages and professions around the world. Many of them expressed the wish that a new version of the book would be published, which, while retaining the essence of A Brief History of Time, would explain the most important concepts in a simpler and more entertaining way. Although some people seemed to expect it to be A Long History of Time, the feedback from readers was unmistakable: very few of them are eager to get acquainted with a voluminous treatise that sets out the subject at the level of a university course in cosmology. Therefore, while working on The Briefest History of Time, we retained and even expanded the fundamental essence of the first book, but at the same time tried to leave unchanged its volume and accessibility of presentation. This is indeed the shortest history, since we have omitted some purely technical aspects, however, as it seems to us, this gap is more than filled with a deeper treatment of the material that truly constitutes the core of the book.
We also took the opportunity to update the information and include the latest theoretical and experimental data in the book. The Shortest History of Time describes the progress that has been made towards a complete unified theory in recent times. In particular, it deals with the latest provisions of string theory, wave-particle duality, and reveals the connection between various physical theories, indicating that a unified theory exists. As for practical research, the book contains important results of the latest observations obtained, in particular, with the help of the COBE (Cosmic Background Explorer) satellite and the Hubble Space Telescope.
Chapter one
THINKING ABOUT THE UNIVERSE
We live in a strange and wonderful universe. Extraordinary imagination is required to appreciate her age, size, fury and even beauty. The place occupied by people in this boundless cosmos may seem insignificant. And yet we are trying to understand how this whole world works and how we humans look in it.
Several decades ago, a famous scientist (some say it was Bertrand Russell) gave a public lecture on astronomy. He said that the Earth revolves around the Sun, and it, in turn, revolves around the center of a vast star system called our Galaxy. At the end of the lecture, a little old lady sitting in the back stood up and said:
You've been telling us complete nonsense here. In reality, the world is a flat slab resting on the back of a giant tortoise.
Smiling with a sense of superiority, the scientist asked:
What is the turtle standing on?
You are a very clever young man, very,” replied the old lady. - She stands on another turtle, and so on, ad infinitum!
Today, most people would find this picture of the universe, this never-ending tower of turtles, pretty funny. But what makes us think we know more?
Forget for a moment what you know - or think you know - about space. Gaze into the night sky. What do all these luminous dots seem to you? Maybe it's tiny lights? It is difficult for us to guess what they really are, because this reality is too far from our everyday experience.
If you often watch the night sky, then you have probably noticed a glimmer of light just above the horizon in the twilight. This is Mercury, a planet very different from our own. A day on Mercury lasts two-thirds of its year. On the sunny side, the temperature exceeds 400°C, and in the dead of night it drops to almost -200°C.
But no matter how different Mercury is from our planet, it is even more difficult to imagine an ordinary star - a colossal inferno that burns millions of tons of matter every second and is heated in the center to tens of millions of degrees.
Another thing that is hard to wrap my head around is the distances to planets and stars. The ancient Chinese built stone towers to see them up close. It is quite natural to think that the stars and planets are much closer than they actually are, because in everyday life we never come into contact with huge cosmic distances.
These distances are so great that it makes no sense to express them in the usual units - meters or kilometers. Light years are used instead (a light year is the path that light travels in a year). In one second, a beam of light travels 300,000 kilometers, so a light year is a very long distance. The nearest star to us (after the Sun) - Proxima Centauri - is about four light years away. This is so far away that the fastest spacecraft currently being designed would fly to it for about ten thousand years. Even in ancient times, people tried to comprehend the nature of the Universe, but they did not have the possibilities that modern science, in particular mathematics, opens up. Today we have powerful tools at our disposal: mental ones, like mathematics and the scientific method of cognition, and technological ones, like computers and telescopes. With their help, scientists have collected together a huge amount of information about space. But what do we really know about the universe, and how did we know it? Where did she come from? In what direction is it developing? Did it have a beginning, and if it did, what was it before him? What is the nature of time? Will it end? Is it possible to go back in time? Recent major physical discoveries, thanks in part to new technologies, offer answers to some of these age-old questions. Perhaps someday these answers will become as obvious as the revolution of the Earth around the Sun - or perhaps as curious as a tower of turtles. Only time (whatever it is) will tell.
What is Stephen Hawking's "A Brief History of Time" about?
From open sources
Today, March 14, the famous English theoretical physicist Stephen Hawking died at the age of 77. the site publishes an abstract of his popular science book "A Brief History of Time: From the Big Bang to Black Holes" (1988), which became a bestseller
The book of the outstanding English physicist Stephen Hawking "A Brief History of Time: from the Big Bang to Black Holes" is dedicated to finding an answer to Einstein's question: "What choice did God have when he created the Universe?" Warned that each formula included in the book will halve the number of buyers, Hawking lays out in accessible language the ideas of the quantum theory of gravity - an unfinished field of physics that combines general relativity and quantum mechanics.
The book begins with a story about the evolution of human ideas about the Universe: from the celestial spheres of the geocentric system of Aristotle and Ptolemy to the realization that the Sun is an ordinary yellow star of medium size in one of the arms of a spiral galaxy - among hundreds of billions of other galaxies in the observable part of the Universe. The discovery of the redshift of the spectra of stars in other galaxies meant that the universe was expanding, and this led to the big bang hypothesis: ten or twenty billion years ago, all objects in the universe could be in one place with an infinitely high density (singularity point).
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The Big Bang is the beginning of time. There is no answer to the question of what was before the Big Bang, since scientific laws cease to work at the point of singularity; the ability to predict the future is lost, and therefore, if something happened "before", then it will not affect current events in any way. After the Big Bang, two scenarios are possible: either the expansion of the Universe will continue forever, or it will stop at some point and go into a contraction phase, which will end with a return to the singularity - the Big Bang. It is not clear which option will be realized - it depends on the distances between the galaxies and the total mass of the matter of the Universe, and these quantities are not exactly known.
Singularities can be in the Universe even after the Big Bang. The star, having used up nuclear fuel, begins to shrink, and with a sufficiently large mass, it cannot resist gravitational collapse, turning into a black hole. So, the English mathematician and physicist Roger Penrose showed that the volume of a star tends to zero, and the density of its matter and the curvature of space-time - to infinity. In other words, a black hole is a singularity in spacetime.
By reversing the direction of time, Penrose and Hawking proved that if general relativity (GR) is correct, then the Big Bang point must exist. So the big bang hypothesis became a mathematical theorem, and general relativity itself turned out to be incomplete: its laws are violated at the singularity point. This is not surprising, because general relativity is a classical theory, and in a small region of space near a singularity, quantum effects become significant. Thus, the study of black holes and the early Universe requires the involvement of quantum mechanics and the creation of a unified theory - the quantum theory of gravity.
Dealing with the phenomena of the microworld, quantum mechanics developed independently of general relativity. In quantum physics, some experience has been accumulated in combining various types of interactions. So, it was possible to combine electromagnetic and weak interactions into one theory. Namely, it turned out that the carriers of the electromagnetic interaction (virtual photons) and the carriers of the weak interaction (vector bosons) are realizations of one particle and become indistinguishable from each other at energies of about 100 GeV. There are also theories of grand unification, that is, the unification of the electroweak and strong interactions (however, to achieve the energies of the grand unification and test these theories, an accelerator the size of the solar system is needed).
All these theories do not include gravity, since it is very small for elementary particles. However, at the singularity point, the gravitational forces, together with the curvature of space-time, tend to infinity, so that the joint consideration of quantum mechanical and gravitational effects becomes inevitable. This leads to the following surprising results.
By the Penrose–Hawking theorem, falling into a black hole is irreversible. But, as is known, any irreversible process is accompanied by an increase in entropy. Does a black hole have entropy?
Hawking notes that the area of the event horizon of a black hole does not decrease with time (and increases when matter falls into a black hole), that is, it has all the properties of entropy. His American colleague Bickenstein proposes to consider the area of the event horizon of a black hole as a measure of its entropy. Hawking argues that, having entropy, a black hole must have a temperature and therefore radiate - contrary to the very definition of a black hole! - but later he himself discovers the mechanism of this radiation.
The source of radiation is the vacuum near the black hole, in which particle-antiparticle pairs are born due to quantum energy fluctuations. One member of the pair has positive energy, the other has negative energy (so the sum is zero); a particle with negative energy can fall into a black hole, and a particle with positive energy can leave its vicinity. The flow of particles of positive energy is the radiation of a black hole; particles with negative energy reduce its mass - the black hole "evaporates" and eventually disappears, taking the singularity with it. In this, Hawking sees the first indication of the possibility of eliminating singularities in general relativity with the help of quantum mechanics and asks the question: will quantum mechanics have a similar effect on "large" singularities, that is, will quantum mechanics eliminate the Big Bang and Big Bang singularities?
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The classical general theory of relativity leaves no choice: the expanding universe is born from a singularity, and the initial conditions are unknown (GR does not work at the "moment of creation"). At the initial moment, the Universe could be ordered and homogeneous, or it could be quite chaotic. The further process of evolution, however, essentially depends on the conditions on this boundary of space-time. Using the Feynman method, summation over various "trajectories" of the development of the Universe, Hawking, within the framework of the quantum theory of gravity, obtains an alternative to singularity: space-time is finite and does not have a singularity in the form of a boundary or edge (this is similar to the surface of the Earth, but only in four dimensions) . And since there is no boundary, there is no need for initial conditions on it, that is, there is no need to introduce new laws that determine the behavior of the early Universe (or resort to the help of God). Then the Universe "... would not have been created, it could not be destroyed. It would simply exist."
The theme of God is present throughout the book; in essence, Hawking is having a discussion with God. Here is a quotation that sums up this discussion in a way.
"From the idea that space and time form a closed surface, there are also very important consequences regarding the role of God in the life of the Universe. In connection with the successes achieved by scientific theories in describing events, most scientists have come to believe that God allows the Universe to develop in according to a certain system of laws and does not interfere with its development, does not violate these laws.But the laws do not tell us anything about what the Universe looked like when it first appeared - winding the clock and choosing the beginning could still be the work of God. we believe that the Universe had a beginning, we can think that it had a Creator.If the Universe is really completely closed and has no boundaries or edges, then it should have no beginning and no end: it simply is and that's it! Is there then room for the Creator?"
Here is the answer to Einstein's question: God had no freedom to choose the initial conditions.
By summing over Feynman trajectories, assuming no space-time boundaries, Hawking finds that the Universe in its current state should, with a high probability, expand equally rapidly in all directions, in agreement with observations of the isotropic CMB background. Further, since the origin of time is a smooth, regular point of space and time, the Universe began to evolve from a homogeneous, ordered state. This initial ordering explains the presence of the thermodynamic arrow of time, indicating the direction of time in which the disorder (entropy) of the Universe increases.
In the final part of the book, Hawking describes string theory, which claims to unify all of physics. This theory does not deal with particles, but with objects like one-dimensional strings. Particles are interpreted as vibrations of strings, emission and absorption of particles - as a break and connection of strings. String theory, however, does not lead to contradictions only in 10-dimensional or 26-dimensional spaces. Perhaps, in the course of the development of the Universe, only four coordinates of our space-time "turned around", while the rest turned out to be folded into a space of negligibly small sizes.
Why did it happen? Hawking gives the answer from the standpoint of the so-called anthropic principle: otherwise the conditions for the development of intelligent beings capable of asking such a question would not have arisen. Indeed, in the case of a smaller dimension of space, evolution is difficult: for example, any through passage in the body of a two-dimensional being divides it into two parts. In spaces of higher dimensions, the law of gravitational attraction will be different, and the orbits of the planets will become unstable ("we would then either freeze or burn out"). Of course, other universes are also possible, with a different number of unfolded coordinates, "... but in such regions there will be no intelligent beings who could see this variety of active dimensions."
Hawking is optimistic about the prospects for creating a unified theory that describes the universe. Having taken away the act of creation from God, he assigns to God the role of the creator of its laws. When a mathematical model is built, the question remains why the universe, subject to this model, exists at all. Not bound by the need to build new theories, scientists will turn to its study. "And if an answer to such a question is found, it will be a complete triumph of the human mind, for then we will understand the plan of God."
Abstract of Stephen Hawking's book "A Brief History of Time" prepared by Igor Yakovlev
