The book “Unreal reality. Traveling the Quantum Loop »

Hello, habrozhiteli! What is time and space? Where does matter come from? What is reality?

“The main paradox of science is that, while revealing to us solid and reliable knowledge of nature, it at the same time is rapidly changing its created ideas about reality. This paradoxicality is best reflected in the book of Carlo Rovelli, which is devoted to the most acute problem of modern fundamental physics - the search for the quantum theory of gravity. Many people heard this name in the series “The Big Bang Theory,” but there was almost nowhere to find out what the meaning of loop gravity was. Meanwhile, this theory is one of the important players at the forefront of fundamental physics, ”- Alexander Sergeyev, co-founder, author of tasks and zavlab of the Open Laboratory project.

Excerpt. Time is not what we think of it

The fact that the nature of time is different from the generally accepted notions that all of us have, it became clear more than a century ago. Special and general theories of relativity made this obvious. Today, the inadequacy of our everyday notions of time can easily be demonstrated in the laboratory.



Consider, for example, the first corollary of the general theory of relativity described in chapter 3. Take two hours, make sure that they show exactly the same time, put some of them on the floor, and others on the table. We will wait half an hour and put them next to them again. Will they still show the same time?



As stated in chapter 3, the answer will be no. Ordinary watches or those that are built into a mobile phone do not have the necessary accuracy to verify this fact. However, physical laboratories around the world have watches that have accuracy that can demonstrate the discrepancy: the clock left on the floor is slower than the same clock above.



Why? Because time does not flow equally everywhere in the world. In some places, its flow is faster, in others - slower. The closer to Earth, where gravity [Gravity potential - Ed .] Is stronger, the slower the time flows. Remember the twins from chapter 3, whose age began to differ as a result of the fact that one lived by the sea and the other in the mountains? This effect is negligible - the time gain obtained by a coastal resident over his whole life in comparison with a mountaineer is a fraction of a second, but such a small value does not change the fact that this is a real difference. Time does not behave the way we are used to imagining.



We should not think about time as if somewhere there are great cosmic clocks that measure the life of the universe. For over 100 years, we know that time should be thought of as a local phenomenon: each object in the Universe has its own time, the pace of which is determined by the local gravitational field.



But even this idea of ​​local time ceases to work when we take into account the quantum nature of the gravitational field. Quantum events on the Planck scale are no longer ordered by the passage of time. Time, in a sense, ceases to exist.



What do the words mean that time does not exist?



First of all, the absence of a temporary variable in the fundamental equations does not mean that everything becomes motionless and that any changes cease to occur. On the contrary, this means that change is omnipresent. That's just elementary processes can not be ordered along the usual sequence of moments. On an extremely small scale, corresponding to the quanta of space, the dance of nature does not obey the rhythm set by one conductor stick for the entire orchestra: each process dances independently of its neighbors, following its own rhythm. The passage of time is an internal property of the world, it is born by the world itself from the relations between quantum events, which are the world and which themselves generate their own time.



In fact, the non-existence of time does not mean anything particularly complicated. Let's try to understand this.

Pulse and chandelier with candles

Time is included in most equations of classical physics. This is a variable denoted by the letter t . Equations tell us how things change over time . If we know what happened in the past, they allow us to predict the future. More precisely, we measure certain quantities, for example, the position A of the object, the angle B of the deviation of the pendulum, the temperature C of the object, and the physical equations say how these quantities will change in time. They predict the functions A (t) , B (t) , C (t) , etc., which describe the changes in these quantities over time t.



Galileo was the first to understand that the motion of objects on earth can be described by equations as functions of time A (t) , B (t) , C (t) , and the first to write formulas for these equations in explicit form. For example, the first law of terrestrial physics, found by Galileo, described the fall of an object, in other words, showed how its height x changes with the passage of time t [ - Ed .]



To discover and verify this law, Galileo needed two types of measurements. He measured the height x of the subject and the time t . Therefore, he needed a tool for measuring time - a clock.



There was no exact watch in Galileo's time. Galileo himself, in his youth, found a way to make accurate chronometers. He found that pendulum vibrations always have the same duration (regardless of amplitude). Therefore, one can measure time simply by counting the swing of the pendulum. This idea seems so obvious, but only Galileo drew attention to it, before it it did not occur to anyone. This often happens in science.



But in reality, everything is not so simple.



According to legend, this idea illuminated Galileo in the majestic Pisa Cathedral, where he watched the slow swings of a giant chandelier with candles. (The legend is not true, since the chandelier first rocked there many years after the death of Galileo, but the story is still good. And it is possible that something else hung in the cathedral in those days.) The scientist observed these fluctuations during religious service which he obviously was not particularly absorbed in, and measured the duration of each swing of the chandelier, counting the strokes of his own pulse. With growing excitement, he found that the number of strokes is the same for each swing - it did not change when the chandelier slowed down and swayed with an insignificant amplitude. All vibrations had the same duration.



This story sounds wonderful, but if you think about it, it causes bewilderment, and this perplexity leads us to the very essence of the problem of time. How did Galileo know that the beat of his own pulse occurred in equal intervals of time [Especially when he began to worry ... - Ed .]?



Soon after Galileo, doctors began to measure the pulse of their patients using a watch, which, ultimately, was nothing more than a pendulum. It turns out that we used the pulse to make sure the pendulum swings regularly, and then we checked the constancy of the pulse with the help of the pendulum. Don't you think there is some kind of vicious circle here? What would that mean?



In fact, we never measure time by itself, we always measure the physical quantities A , B , C ... (vibrations, pulse, and many other things) and compare one quantity with another, that is, in other words, we measure the functions A (B ) , B (C) , C (A) , etc. We can calculate how many beats of the pulse in each oscillation, how many oscillations occur on each tick of the stopwatch, how many ticks of the stopwatch between beats of the tower clock ...



The bottom line is that it’s convenient for us to imagine that there is a quantity t - “true time” - which underlies all movement, even if it cannot be measured directly. We write down equations for physical variables with respect to this unobservable quantity t - equations that tell us how things change with t : for example, how long each oscillation takes and how long the heartbeat lasts. From here we can deduce how the quantities change in relation to each other - how many beats of the pulse occur in one oscillation - and compare these predictions with what we observe in the world. If these predictions turn out to be correct, we believe that our complex scheme is correct, and in particular the usefulness of the time variable t , even if it cannot be directly measured.



In other words, the existence of a time variable is a convenient assumption, not the result of observations.



The first to understand all this was Newton: he guessed that it was an effective approach, clarified and developed this scheme. Newton openly writes in his book that it is impossible to measure the true time t , but assuming that it exists, an effective construction is obtained for describing nature.



Having clarified this point, we can return to quantum gravity and to the meaning of the statement that "time does not exist." This simply means that the Newtonian scheme ceases to work when we are dealing with very small things. She was good, but only for big things.



If we want to gain a deep understanding of the world, if we want to understand how it functions in situations less familiar to us, in which quantum gravity becomes significant, we will have to abandon this scheme. The idea of ​​time t , which flows by itself and in relation to which things evolve, ceases to be useful. The world is not described by the equations of evolution in time t . We just have to list the variables A , B , C , ... that we really observe, and write down the equations expressing the relations between these variables and nothing else: that is, the equations for the relations A (B) , B (C) , C ( A) , ... that we observe, and not for the functions A (t) , B (t) , C (t) , ... that we do not observe.



In the example with a pulse and a chandelier, instead of the pulse and swings of the chandelier that occur over time, we will only have equations that describe how the two corresponding quantities change relative to each other, that is, an equation that directly tells us how many heartbeats per pulse swing of a chandelier without mention t .



“Physics without time” is physics in which we talk only about the pulse and the chandelier, not mentioning time.



This is a simple change, but from a conceptual point of view it is a huge leap. We must learn to think of the world not as something changing over time, but in some other way. Things change only in relation to each other. At a fundamental level, time does not exist. Our everyday sense of the passage of time is only an approximation that is true for our macroscopic scales. It arises due to the fact that we perceive the world in a very coarse, coarse-grained form.



Thus, the world described by this theory is very far from what we are accustomed to. There is no longer the space that the world contains , and there is no time during which events take place. There are elementary processes in which the quanta of space and matter continuously interact with each other. This picture of the world can be compared to a clean and calm alpine lake, which consists of a myriad of rapidly dancing tiny water molecules. The illusion that we are surrounded by continuous space and time is the result of viewing from afar a dense swarm of elementary processes.

From the author

Throughout my scientific career, friends and just curious people have asked me to explain what is happening in the field of quantum gravity research. How do you manage to find new ways to comprehend space and time? I have repeatedly been asked to tell about these studies in an accessible form. While there are many books on cosmology and string theory, books that describe studies on the quantum nature of space and time, as well as on loop quantum gravity, are almost impossible to find. I hesitated for a long time because I wanted to focus on research. Several years ago, completing a monograph on this topic, I felt that the collective work of many scientists brought this field of research to the stage of maturity when it became possible to write a popular science book. The landscape we are exploring is amazing - is it worth continuing to hide it from other people?



But I continued to postpone the project, because I could not “see” the book in my head. How to describe a world without space and time? In 2012, sitting alone at the wheel on a night road from Italy to France, I suddenly realized that the only way to intelligibly explain the constant modification of the concepts of space and time is to tell the whole story from the very beginning: from the ideas of Democritus to the presentation about quanta of space. In the end, that’s how I myself understand this story. I began to mentally sketch the structure of the book right behind the wheel, getting more and more excited, until I heard the police siren and the demand to stop - I far exceeded the allowed speed. The Italian policeman politely asked me if I had lost my mind to drive at such a speed. I replied that I had just found the idea that I had been looking for so long; he did not write me a fine and wished me luck with the new book. This book is in front of you.



The book was originally written in Italian and first published in 2014. Soon after, I prepared several articles on fundamental physics for an Italian newspaper. The famous Italian publisher Adelphi ordered me an extended version of these articles, which came out in the form of a brochure. So a small book “Seven Short Lectures on Physics” appeared, which, to my great surprise, became an international bestseller and became an occasion for communication with many wonderful readers around the world. Thus, the “Seven Lectures” were written after this book and, to some extent, became a synthesis of some of the issues that are addressed here. If you have already read “Seven Short Lectures on Physics” and want to learn more in order to plunge even deeper into the strange world described in that book, here you will find the necessary details.



Despite the fact that traditional physics is presented in this book from a rather unusual point of view, in general this does not cause controversy. However, that part of the book, which deals with modern research on quantum gravity, reflects my personal understanding of the state of knowledge of this topic. This area of ​​knowledge is on the border between what we understand and what we still don’t understand, so we are still very far from reaching consensus on the main issues related to it. Some of my fellow physicists will agree with what I wrote in this book, others will not. This is a common situation for current research conducted on the borders of our knowledge, but I prefer to talk about it clearly and openly. This book is not about what we are sure of; this book is about adventures on the path to the unknown.



In general, it is about a journey dedicated to one of the most impressive adventures that have befallen humanity: a journey beyond the limits of parochial views of reality to an ever deeper understanding of the structure of things. And this incredible journey beyond the ordinary worldview is far from over.



»More details on the book can be found on the publisher’s website

» Contents

» Excerpt



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