The book “Eternity. In search of the ultimate theory of time "

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    imageWhat is time in the modern sense and why does it possess such properties? Why does time always move in one direction? Why are there irreversible processes? Twenty years ago, Stephen Hawking tried to explain time through the Big Bang theory. Now, Sean Carroll, one of the leading theoretical physicists of our time, will introduce you to the delightful paradigm of the theory of the arrow of time, which covers objects from the entropy of quantum mechanics to time travel in the theory of information and the meaning of life.

    The book “Eternity. In search of the ultimate theory of time ”is not just the next step towards understanding why the Universe exists - it is an excellent read for a wide range of readers who are interested in the physics and structure of our world.

    This book is about the nature of time, about the origin of the Universe and about the fundamental structure of physical reality. Here we do not think in any small, insignificant categories. We consider age-old, thorough problems. Where did time and space come from? Is everything really limited to the Universe that we see, or are there other “Universes” beyond the reach of our eyes? How is the future different from the past?

    According to the authors of the Oxford Dictionary, time is the most commonly used noun in English. Throughout our lives, we move through time, obsessively follow it and try to overtake it every day - and yet, surprisingly, there are few people who can explain in simple words what time is.

    We live in the era of the Internet, so it would be logical to turn to the free Wikipedia encyclopedia for help. At the time of writing this book, the Time article begins with the following words:

    Time is a component of a measuring system used to determine the sequence of events, to compare the duration of events and the intervals between them, and to quantify the movement of objects. Time is one of the main topics of religious, philosophical and scientific research, but even the greatest scientists are not able to define time in a consistent form applicable to all areas of research.

    Let's go. By the end of the book, we will be able to formulate a very precise definition of time, which will be applicable to all areas. Unfortunately, it is much less obvious why time possesses the properties that it possesses, although we will still study some intriguing ideas.

    Cosmology, the doctrine of the entire Universe, has made great progress over the past hundred years. Fourteen billion years ago, our Universe (or at least that part of it that we are able to observe) was in an unimaginably hot, dense state, which we call the Big Bang. Since then, the Universe has been expanding and cooling, and, apparently, it continues to do so in the foreseeable future, and perhaps throughout eternity.

    One hundred years ago, none of this was known to us - scientists practically had no idea about the structure of the Universe outside the Milky Way galaxy. Today, when we were able to take measurements from the observed Universe, we are able to describe in detail not only its size and shape, but also the constituent parts and the approximate course of history. However, we still cannot answer many important questions, in particular related to the first moments of the Big Bang. As we learn, these issues play a critically important role in our understanding of time - not only in the vast expanses of space, but also in our laboratories on Earth and even in our daily lives.

    Time after the Big Bang

    Obviously, over time, the Universe is evolving: the early Universe was hot and dense, the modern Universe is cold and sparse. But I'm going to outline much deeper connections. The most mysterious characteristic of time is its orientation: the past is different from the future. This is the arrow of time. Unlike the directions in space, which are equally equal among themselves, the Universe undoubtedly has a preferred orientation in time. The main theme of this book is that the arrow of time exists because the universe evolves in a certain way.

    The reason why time has a direction lies in the fact that the Universe is full of irreversible processes - events that occur in one direction of time, but never in another. You can turn an egg into an omelet, as in the classic example, but it is impossible to make an entire egg from an omelet. Milk is mixed with coffee; fuel burns and turns into exhaust gases; people are born, mature and die. In Nature, we everywhere find sequences of events in which one type of event always precedes another, and the other always follows after. Together, they define the arrow of time.

    It is noteworthy that the whole of our understanding of irreversible processes is based on a single concept - what is called entropy and measures the "disorder" of an object or a cluster of objects. Over time, entropy stubbornly increases, or at least remains constant - this is the famous second law of thermodynamics. 2 And the reason why entropy tends to increase is deceptively simple: there are many more ways to make a mess than to organize an order; therefore (ceteris paribus), ordered configurations will naturally flow into increasingly disordered ones. It’s not difficult to mix the egg molecules in order to get an omelet, but to carefully collect them back to form an entire egg, we can’t do it.

    This is the end of the traditional story that physicists usually tell about themselves. But there is another ingredient of incredible importance, which so far has not received due attention: if everything in the Universe is evolving in the direction of increasing disorder, then it should have started with an incredibly ordered configuration. This whole logical chain explaining why it is impossible to turn an omelet into an egg is obviously based on a fundamental assumption regarding the early Universe: it was in a state of very low entropy and very high ordering.

    The arrow of time connects the early Universe with what we literally experience at every moment of our lives. This is not only breaking eggs and other irreversible processes, such as adding milk to coffee or cluttering up a room in which no one is cleaning. The arrow of time is the reason why it seems to us that time flows past us or (if you like) why we are floating through time. This is the reason why we remember the past, but not the future. Why we grow and change, why we have a metabolic process and why we die in the end. Why do we believe in a causal relationship. This is a fundamental component of our concept of free will.
    And all this thanks to the Big Bang.

    We see far from everything

    The riddle of the arrow of time, in fact, boils down to the following: why the conditions in the early Universe were exactly what they were; why was there a configuration with low entropy that allowed all these interesting and irreversible processes to happen? This book is the subject of research. Unfortunately, no one knows the correct answer yet. But in the development of modern science, we have reached the stage at which we already have the necessary tools in order to seriously tackle this riddle.

    Both scientists and ancient thinkers have always tried to understand time. In ancient Greece, the philosophers of pre-Socratic times Heraclitus and Parmenides held different positions on the nature of time: Heraclitus emphasized the primacy of change, while Parmenides denied the reality of change in general. The nineteenth century was the heroic era of statistical mechanics: people learned to establish the behavior of macroscopic objects based on their microscopic components - when figures such as Ludwig Boltzmann, James Clerk Maxwell and Josiah Willard Gibbs managed to define entropy and describe its role in irreversible processes . However, they did not know anything about Einstein's general theory of relativity or about quantum mechanics, and certainly, about modern cosmology.

    I am going to propose the following version: The Big Bang was not the beginning of the Universe. Cosmologists sometimes say that the Big Bang represents the true boundary of space and time, before which nothing existed - in fact, even time itself did not exist, therefore the concept of “before”, strictly speaking, cannot be applied in this case. However, we know too little about the final laws of physics to make such statements with confidence. Scientists are increasingly starting to appeal to the possibility that the Big Bang was not really the beginning of everything - this is just the phase through which the Universe or at least our part of the Universe passes. If this is true, then the question of our low-entropy beginning takes a different form: not "Why did the Universe originate in such a low-entropy state?",

    Although this question does not seem simpler, it is another question, and it opens up a new range of possible answers for us. It is possible that the Universe that we see is just a part of the much larger Multiverse, which does not arise in a low-entropy configuration. I will argue that the most reasonable model of the Multiverse is one where entropy increases simply because entropy can always increase: there is no state of maximum entropy. As an added bonus, the Multiverse can be absolutely symmetrical in time: starting at some point in the middle, when entropy is high, it evolves toward the past and future into states in which entropy is even higher. The universe, accessible to our eyes, is just a tiny process of an incredibly massive ensemble,

    In any case, this is just one of the possibilities. Consider this an example of one of the scenarios that cosmologists should consider if they decide to take seriously the problems posed by the arrow of time. And regardless of whether this particular idea leads us in the right direction, these problems themselves are already incredibly exciting and real. Throughout this book, we will study the problems of time from many different points of view: time travel, information, quantum mechanics, the nature of eternity. When there is still no certainty as to how the final answer should sound, you should try to ask the question in every way possible.

    There will always be skeptics

    Not everyone agrees that cosmology should play a significant role in our understanding of the arrow of time. Once I had a chance to hold a seminar on this subject in a large audience at the physics department of a major educational institution. One of the senior professors of this faculty considered my presentation insufficiently convincing and made efforts so that all those present would learn about his displeasure. The next day, he sent an e-mail to other faculty members and was kind enough to include me in the mailing list:

    Finally, the magnitude of the entropy of the Universe as a function of time is an interesting problem for cosmology, but to assume that the laws of physics depend on it is utter nonsense. Carroll’s claim that the second law of thermodynamics owes its existence to cosmology is one of the stupidest [sic] statements that I have heard at physical seminars, with the exception of the statement [surname cut out] about consciousness in quantum mechanics. I am surprised that the physicists present kindly listened to such nonsense. Later, I had dinner with several graduate students who readily supported my objections, but Carroll remained unshakable.

    I hope he reads this book. It contains a lot of high-profile statements, but I will use caution, dividing them into three types: 1) the remarkable results of modern physics, which sound surprising, but nevertheless are generally recognized facts; 2) large-scale statements, with which not all working physicists agree, but which nevertheless must be accepted, since their truthfulness does not raise any questions; 3) speculative ideas outside the comfort zone of the current state of affairs in science. Definitely, we will not shy away from abstract and speculative reasoning, but they will always be clearly indicated as such. Ultimately, you will be armed with all the necessary knowledge in order to independently decide which parts of the story make sense and which do not.

    The theme of time includes a huge number of ideas - from everyday to shocking. We will look into thermodynamics, quantum mechanics, special and general theories of relativity, information theory, cosmology, elementary particle physics and quantum gravity. The first part of the book can be considered as a sightseeing tour, telling about the entropy and arrow of time, the evolution of the Universe and various concepts of the idea of ​​“time” itself. After that we will try to approach the issue more systematically: in the second part we will think deeply about space — time and relativity, including the possibility of traveling backward in time. In the third part, we will seriously consider the concept of entropy, having studied its role in a variety of contexts - from the evolution of life to the mysteries of quantum mechanics.

    In the fourth part we will put it all together in order to boldly look into the eyes of the riddles that entropy poses to modern cosmologists: how should the Universe look like and how much does it look like how the Universe actually looks like? I will demonstrate that the Universe looks completely different from what it “should” (of course, explaining what I mean by using this word) - at least, this is the case for the Universe that we see around us. If our Universe was born in the Big Bang, then its existence is burdened by a finely tuned boundary condition for which we cannot find a worthy explanation. However, if the observed Universe is part of a larger ensemble - the Multiverse, then perhaps we have a chance to explain

    All this, of course, is an unforgivable theorizing, but these fabrications should be taken seriously. The stakes are great - time, space, the Universe, so the mistakes that we will certainly make along the way, no doubt, will also be large-scale. It is sometimes useful to let your imagination go free swimming, even if our ultimate goal is to return to Earth and explain what is happening in the kitchen.

    The book can be found in more detail on the publisher's website.

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