The book "Cosmic Landscape. String Theory and the Illusion of Intelligent Design of the Universe "

    imageLeonard Susskind, a famous American physicist and one of the founders of string theory, at one time proposed a revolutionary concept of understanding the Universe and the place of man in it. With his research, Susskind inspired a whole galaxy of modern physicists who believed that this theory could uniquely predict the properties of our Universe. Now, in his first book for a wide range of readers, Susskind refines and rethinks his views, arguing that this idea is by no means universal and it will have to give way to a much broader concept of a giant "cosmic landscape."

    Studies of the beginning of the XXI century allowed science to rise to a new level in the knowledge of the world, says Susskind. And this fascinating book, which takes the reader to the forefront of battles in modern physics, is a clear confirmation of this.

    Elegant supersymmetric Universe?


    The real principles underlying string theory are shrouded in great mystery. Almost everything we know about theory includes a special part of the landscape, where mathematics is remarkably simplified thanks to a property called supersymmetry. Supersymmetric areas of the landscape form a perfectly flat plain, located at a height exactly equal to zero, with properties so symmetrical that many things can be calculated without information about the entire landscape. If someone was looking for simplicity and elegance, then the flat plain of supersymmetric string theory, also known as superstring theory, is exactly the place to which they should pay attention. In fact, a couple of years ago this place was the only one that string theorists paid attention to. But some of the physicists have already shaken off their enchanting delusion and are trying to get rid of the elegant simplifications of the super world. The reason is simple: the real world is not supersymmetric.

    A world containing a Standard Model and a small non-zero cosmological constant cannot be located on a plane of zero height. It lies somewhere in the uneven region of the Landscape with hills, valleys, high plateaus and steep slopes. But there is reason to believe that our valley is close to the supersymmetric part of the Landscape and that some remnants of the mathematical superchud could help us understand the features of the empirical world. One example that we will examine in this section is the Higgs boson mass. In fact, all the discoveries due to which this book came into being represent the first tentative attempts to move away from the safe supersymmetric plain.

    Supersymmetry tells us about the differences and similarities of bosons and fermions. Like so much more in modern physics, the principles of supersymmetry can be traced back to the first works of Einstein. In 2005, we celebrated the centenary of the “anno mirabilis” - the year of the wonders of modern physics. Einstein began two revolutions this year and completed the third. Of course, this was the year of the special theory of relativity. But few know that 1905 was much more than the "year of relativity." He also marked the birth of photons, the beginning of modern quantum mechanics.

    Einstein received only one Nobel Prize in Physics, although I think that every Nobel Prize awarded after 1905 carried the echoes of Einstein's discoveries. The Nobel Prize was awarded to Einstein not for creating the theory of relativity, but for explaining the photoelectric effect. It was the photoelectric effect theory that was the most radical contribution of Einstein to physics, where he first introduced the concept of photons, energy quanta, of which light consists. Physics was already ready to give birth to a special theory of relativity, its creation was only a matter of time, while the photon theory of light thundered like thunder out of a clear sky. Einstein showed that a ray of light, usually represented as a wave phenomenon, has a discrete structure. If the light has a certain color (wavelength), then all the photons are marching up: each photon is identical to any other. Particles that can simultaneously be in the same quantum state are called bosons in honor of the Indian physicist Satiendranath Bose.

    Almost twenty years later, completing the building laid by Einstein, Louis de Broglie will show that electrons, always perceived as particles, behave at the same time and like waves. Like waves, electrons are able to reflect, refract, diffract and interfere. But there is a fundamental difference between electrons and photons: unlike photons, two electrons cannot simultaneously be in the same quantum state. Pauli’s prohibition principle ensures that every electron in an atom has its own quantum state and that no other electron can stick its nose in an already occupied place. Even outside an atom, two identical electrons cannot be in the same place or have the same momentum. Particles of this kind are called fermions by the name of the Italian physicist Enrico Fermi, although in fairness they should be called the Pauli. Of all the particles of the Standard Model, about half are fermions (electrons, neutrinos, and quarks), and the other half are bosons (photons, Z and W bosons, gluons, and the Higgs boson).

    Fermions and bosons play different roles in the picture of the world. Usually we represent matter consisting of atoms, that is, of electrons and nuclei. In the first approximation, nuclei consist of protons and neutrons held together by nuclear forces, but at a deeper level, protons and neutrons are assembled from small building blocks — quarks. All these particles - electrons, protons, neutrons and quarks - are fermions. Matter consists of fermions. But without bosons, atoms, nuclei, protons and neutrons will simply fall apart. These bosons, primarily photons and gluons, jumping back and forth between fermions, create gravitational forces that hold everything together. Although fermions and bosons are critically important for the world to be as it is, they have always been considered "animals of a different breed."

    But around the early 1970s, theorists inspired by the first successes of string theory began to play with new mathematical ideas, according to which fermions and bosons are actually not so different. One idea was that all particles form ideal pairs of identical twins, identical in all respects, except that one of them is a fermion and the other is a boson. It was a completely wild conjecture. Its validity for the real world would mean that physicists somehow managed to lose half of all elementary particles, failing to detect them in their laboratories. For example, according to this hypothesis, there must exist a particle with exactly the same mass, charge, and other properties as that of an electron, only being not a fermion, but a boson. How was it possible not to notice such a particle at the Stanford or CERN accelerators? Supersymmetry implies the existence of a massless neutral fermion twin in a photon, as well as boson twins in electrons and quarks. That is, the hypothesis predicted a whole world of mysteriously missing "opposites". In fact, all this work was only a mathematical game, a purely theoretical study of a new kind of symmetry - a world that does not exist, but that could exist.

    Identical twin particles do not exist. Physicists did not bother and did not miss the whole parallel world. What interest then is this mathematical speculation, and why has this interest suddenly intensified in the last 30 years? Physicists have always been interested in all sorts of mathematical symmetries, even if the only reasonable question that could be asked: “Why is this symmetry not found in nature?” But both the real world and its physical description are full of various symmetries. Symmetry is one of the most long-range and powerful tools in the arsenal of theoretical physics. It permeates all sections of modern physics, and especially those related to quantum mechanics. In many cases, the type of symmetry is all we know about the physical system, but symmetry analysis is such a powerful method which often tells us almost everything we want to know. Symmetries are often the garden in which physicists find aesthetic satisfaction from their theories. But what is symmetry?

    Let's start with a snowflake. Every child knows that there are no two identical snowflakes, but at the same time they all have a common feature, namely symmetry. The symmetry of the snowflake immediately catches the eye. If you take a snowflake and turn it to an arbitrary angle, then it will look different from its original form - turned. But if you turn the snowflake exactly 60 °, then it will coincide with itself. The physicist might say that turning a snowflake by 60 ° is a symmetry.

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    Symmetries are associated with operations or transformations that can be performed on the system without affecting the result of the experiment. In the case of a snowflake, such an operation is a 60 ° rotation. Here is another example: suppose that we set up an experiment aimed at measuring the acceleration of free fall on the surface of the Earth. The simplest option would be to drop a stone from a known height and measure the time of its fall. Answer: about 10 meters per second per second. Please note that I am not worried about telling you where I dropped a stone: in California or in Calcutta. In a very good approximation, the answer will be the same anywhere on the surface of the Earth: the result of the experiment will not change if you move with all the experimental equipment from one place of the earth's surface to another. In physical jargon, shifting or moving something from one point to another is called translation. Therefore, on the gravitational field of the Earth, we can say that it has “translational symmetry”. Of course, some side effects may introduce disturbances in the results of our experiment and spoil the symmetry. For example, conducting an experiment on very large and massive mineral deposits, we will get a little more importance than in other places. In this case, we would say that symmetry is only approximate. Approximate symmetry is also called broken symmetry. The presence of individual deposits of heavy minerals "breaks the translational symmetry." Some side effects may introduce disturbances in the results of our experiment and spoil the symmetry. For example, conducting an experiment on very large and massive mineral deposits, we will get a little more importance than in other places. In this case, we would say that symmetry is only approximate. Approximate symmetry is also called broken symmetry. The presence of individual deposits of heavy minerals "breaks the translational symmetry." Some side effects may introduce disturbances in the results of our experiment and spoil the symmetry. For example, conducting an experiment on very large and massive mineral deposits, we will get a little more importance than in other places. In this case, we would say that symmetry is only approximate. Approximate symmetry is also called broken symmetry. The presence of individual deposits of heavy minerals "breaks the translational symmetry." Approximate symmetry is also called broken symmetry. The presence of individual deposits of heavy minerals "breaks the translational symmetry." Approximate symmetry is also called broken symmetry. The presence of individual deposits of heavy minerals "breaks the translational symmetry."

    Can the symmetry of a snowflake be broken? No doubt some snowflakes are imperfect. If a snowflake is formed in non-ideal conditions, then one side may differ from the other. It will still have a shape close to hexagonal, but this hexagon will be imperfect, that is, its symmetry will be broken.

    In outer space, far from any disturbing influences, we could measure the gravitational force between the two masses and get the Newtonian law of the world. Regardless of where the experiment was conducted, we, in theory, should receive the same answer. Thus, the Newtonian law of the world has a translational invariance.

    To measure the force of attraction between two objects, you need to place them at some distance from each other. For example, we can arrange two objects so that the straight line connecting them will be parallel to the x axis in some given coordinate system. With equal success, we can arrange objects on a straight line parallel to the y axis. Will the force of attraction measured by us depend on the direction of the straight line connecting these objects? In principle, yes, but only if the laws of nature differ from those that we have. In nature, the law of world wideness claims that the force of attraction is proportional to the product of the masses and inversely proportional to the square of the distance between them and it does not depend on the orientation of one object relative to another. Directional independence is called rotational symmetry.

    Look in the mirror. Your reflection is like two peas in a pod like you. The mirror image of your pants is no different from the pants themselves. The reflection of the left glove exactly repeats the left glove.

    Stop. Something is wrong here. Let's look again carefully. The mirror image of the left glove is not all identical to the left glove. It is identical to the right glove! And the mirror image of the right glove is identical to the left glove.

    Now look more attentively at your own reflection. It's not you. The mole you have on your left cheek, your reflection on your right. And if you opened your own chest, you would find that the heart of your reflection is not on the left, as in all normal people, but on the right. Let's call the mirror man - man.

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    Suppose that we have a futuristic technology that allows us to collect any object we want from individual atoms. We will build with the help of this technology a person whose mirror image will exactly repeat you: the heart on the left, the freckle on the left, etc. Then the original, which we build, will be a man.

    Will a person function normally? Will he breathe? Will his heart beat? If you give him candy, will he assimilate the sugar that is part of it? The answers to most of these questions are yes. Basically, the person will function in the same way as the person. But with his metabolism will have problems. He will not be able to assimilate ordinary sugar. The reason is that sugar exists in two mirror forms, like the right and left gloves. A person is able to assimilate only one of the mirror forms of sugar. A person is able to absorb only sugar. Molecules - sugar and sugar - differ from each other in the same way as the right and left glove. Chemists call ordinary sugars that a person is capable of assimilating, D-isomers (from Latin dextra - right), and mirror them, which only a person can absorb,

    Replacing something with its mirror image is called mirror symmetry, or parity. The consequences of mirror reflection are, in principle, obvious, but let's repeat one important thing again: if everything in the world is replaced with its mirror reflection, then the behavior of this world will in no way change and will not differ from the behavior of our world.

    In fact, mirror symmetry is not exact. It is a good example of broken symmetry. Something leads to the fact that the mirror image of a neutrino is many times heavier than the original. This applies to all other particles, although to a much lesser extent. It seems that the great world mirror is slightly crooked, it distorts the reflection a little. But this distortion is so insignificant that it practically does not affect ordinary matter. But in the behavior of high-energy particles in the mirror world can occur very significant changes. However, for the time being, let's pretend that mirror symmetry in nature is accurate.

    What do we mean when we say that a symmetry relation exists between particles? In a nutshell, this means that each type of particle has a partner or a twin with very similar properties. For mirror symmetry, this means that if the laws of nature allow for the existence of a left glove, then the existence of a right glove is also possible. Establishing the existence of D-glucose means that L-glucose must exist. And if the mirror symmetry is not broken, the same should apply to all elementary particles. Each particle must have a twin, identical to it up to specular reflection. When a person is mirrored, each elementary particle that makes up his body is replaced by its mirror twin.

    Antimatter is another type of symmetry, called charge conjugation symmetry. Since symmetry implies the replacement of everything with its symmetric counterpart, the symmetry of charge conjugation involves the replacement of each particle by its antiparticle. It changes the positive electric charges, for example, protons, into negative ones, in this case antiprotons. Similarly, negatively charged electrons are replaced by positively charged positrons. Hydrogen atoms are replaced by antihydrogen atoms consisting of positrons and antiprotons. Such atoms are actually obtained in laboratories, however, in very small quantities, insufficient even to build antimolecules from them. But no one doubts that anti-molecules are possible. Similarly, anti-humans are possible, but do not forget that you will have to feed them with anti-food. In fact, it is better to keep anti-people and ordinary people away from each other. When a substance encounters antimatter, they destroy each other, turning into photons. The explosion that will occur if you accidentally shake the hand of an antihuman will be stronger than the hydrogen bomb explosion.

    As it turned out, the charge-conjugation symmetry is also slightly broken. But, as in the case of mirror symmetry, the effect of this violation turns out to be quite insignificant, if not to take into account particles of very high energies. Now back to the fermions and bosons. The original, very first string theory that Nambu and I developed is called the bosonic string theory, because all the particles it describes are bosons. It is not quite suitable for describing hadrons, because, after all, the proton is a fermion. Similarly, it is not suitable for the role of the theory of everything. Electrons, neutrinos, quarks are all fermions. But not much time passed and a new version of string theory appeared, which already contained not only bosons, but also fermions.

    Supersymmetry has proven to be an indispensable and extremely powerful mathematical tool for string theorists. Without it, mathematics is so complicated that it is very difficult to establish the fact of consistency of the theory. Almost all credible theories claiming to describe the real world are supersymmetric. But, as I have already stressed, supersymmetry in nature is not an exact symmetry. In the best case, this is quite a broken symmetry, resembling the reflection of the world in an extremely crooked mirror. So far, no superpartner has been found for any of the known elementary particles. If in nature there existed a boson with the same mass and charge as that of an electron, it would have been discovered long ago. However, if you open a web browser and search for articles on particle physics on the Internet, you will find that since the mid-1970s, supersymmetry has been one way or another used in the overwhelming majority of works. Why? Why theorists have not yet thrown supersymmetry into the wastebasket along with the theory of superstrings? There are several reasons for this.

    The subject, which was once called high-energy theoretical physics of elementary particles, has long been divided into two disciplines: theoretical and phenomenological. If you enter the URL http://arXiv.org in the address bar of your browserthen you will be taken to the site where physicists publish the preprints of their articles. Different disciplines are divided there into nuclear physics, condensed matter physics, etc. If you go to the section of high-energy physics (hep), you will find there two separate archives: one (hep-ph) contains phenomenological, and the second (hep-th) - theoretical and mathematical articles. Looking into these archives, you will see that the hep-ph section contains articles on traditional particle physics, containing either the results of the experiments carried out or a description of the planned experiments. Usually in these articles there is a large number of tables and graphs. In contrast, in the hep-th section there are mostly articles on string theory and gravity. They are full of mathematical calculations and have very little to do with experiments.

    But in both sections, most articles are somehow related to supersymmetry. Representatives of each have their own reasons for this. For pure theoreticians, such a reason is mathematics - the use of supersymmetry leads to a tremendous simplification of mathematical calculations and allows one to obtain a solution to problems that other methods could have been dealt with incredibly difficult. Remember, in chapter 2, I said that the cosmological constant will be exactly zero if all particles have supersymmetric partners? This is one of the mathematical wonders that appear in supersymmetric theories. I would not like to describe them here, but the main thing is that supersymmetry so simplifies calculations in quantum field theory and string theory that such things become available to theorists, which otherwise they could hardly have withdrawn. And though the real world is not supersymmetric, but supersymmetry allows us to understand some of the existing phenomena, such as black holes. Any theory involving gravity also describes black holes. They have paradoxical and mysterious properties, which we will talk about later. The possible options for resolving these paradoxes are too complex to test in conventional theories. And then, as if by magic, the existence of superpartners makes the study of black holes extremely simple. This simplification is especially valuable for string theorists. The mathematics of string theory, as is customary now, relies almost entirely on supersymmetry. Even many old quantum-mechanical calculations of the behavior of quarks and gluons are greatly simplified by the addition of superpartners.

    Although the end goals of the "hepfer" and "hepter" are the same, the current tasks of the phenomenologists and string theorists differ. Phenomenologists use old methods of theoretical physics and sometimes new ideas of string theory to describe the Laws of Physics in the sense that they were understood throughout most of the 20th century. As a rule, they do not try to build a theory, the only confirmation of the correctness of which would be its mathematical completeness. They are not trying to build a unified theory. Supersymmetry interests them only as an approximation to the broken symmetry of nature to search for something that can then be discovered in laboratory experiments. The most important discovery for them would be the discovery of missing superpartners.

    As you remember, the broken symmetry is not perfect. In an ideal mirror, the object and its reflection are completely identical to within the replacement of the right by the left, but in a curved mirror from the room of laughter, symmetry is imperfect. Such a reflection, perhaps, is only suitable for identifying an object, but it is also a highly distorted copy. The image of a thin man in such a mirror can look like an image of a fat man, weighing several times more than his thin counterpart.

    In the attraction of curved mirrors, called our Universe, the mirror of supersymmetry introduces huge distortions into the reflection of particles, so huge that superpartners of ordinary particles look like incredible fat people in it. If they exist, they must be many times heavier than ordinary particles. No superpartner has been discovered so far: neither the electron superpartner, nor the photon superpartner, nor the quark superpartner. Does this mean that they do not exist at all and that supersymmetry is just a useless mathematical game? It is possible that this is so, but it can also mean that the distortion is so great that the superpartners are too heavy and the energy of modern particle accelerators is not enough to detect them. If for some reason the masses of superpartners exceed several hundred proton masses, they really cannot be detected,

    All superpartners have names that resemble the names of their regular twins. These names are easy to remember if you know the rule. If a common particle is a boson, for example, a photon or a Higgs boson, then the name of its superpartner is formed by adding the suffix "foreign". For example, Fotino, Higsino or Gluino. If the original particle is a fermion, then the name of the superpartner is formed by adding the prefix "c", for example, electron, smyon, snaytrino, squark, etc. This last rule gave rise to the ugliest names that can be found in physics.

    In science, there is a well-established view that new discoveries are waiting for us literally "around the corner." If attempts to discover superpartners in the region of several hundred proton masses fail, the estimates are likely to be revised and the detection of superparticles will be postponed until the accelerators are built to generate particles with masses of a thousand proton masses ... or ten thousand proton masses. Does this not remind you of the desire to wishful thinking? I do not think so. Supersymmetry may turn out to be the key to the riddle of the Higgs particles, and the problem itself may be related to the Mother of all physical problems and the riddle of the inexplicable weakness of the gravitational interaction.

    The same quantum shudder, which leads to an inexplicably high vacuum energy, may also be responsible for the masses of elementary particles. Suppose we put a particle in a quivering vacuum. Interacting with quantum fluctuations, the particle will introduce disturbances in them in close proximity to its location. Some particles will quench quantum fluctuations, others will amplify them. The cumulative effect can be a change in the energy of these fluctuations. This additional energy, arising from the presence of a particle, can be interpreted as some kind of additional mass (think of E = mc2). The most typical example is the attempt to calculate the Higgs boson mass in this way. This results in an absolutely absurd result, similar to the result of an attempt to estimate the vacuum energy.

    Why does this bother us so much? Although theorists usually focus exclusively on the Higgs boson, the problem described applies to all elementary particles, with the exception of the photon and the graviton. Any particle placed in a fluctuating vacuum acquires an abnormally large mass. But if all particles increase their masses, then all the substance of the Universe will become many times heavier and the gravitational forces acting between the bodies will increase by many orders of magnitude. And we remember that even a slight increase in the gravitational constant will lead to a completely uninhabited Universe. This dilemma is called the Higgs mass problem, and it is another problem of fine-tuning the Physics Laws that the theorists are trying to solve. The Higgs mass problem is very similar to the problem of the smallness of the cosmological constant.

    Remember how in the second chapter I talked about the fact that fermions and bosons make opposite contributions to the energy of vacuum fluctuations, and if their contributions could be equalized, would this solve the problem of vacuum energy? This is also true for unwanted additional masses of particles. In a supersymmetric world, the enormous contribution of quantum fluctuations can be tamed, leaving the masses of particles unperturbed. Moreover, even a broken supersymmetry could alleviate the problem if this violation were not too strong. This is the main reason why physicists studying elementary particles hope that supersymmetry is waiting for them "around the corner." However, it should be noted that the broken supersymmetry still cannot explain such an incredibly small value of the cosmological constant.

    The problem of Higgs mass is similar to the problem of vacuum energy on one side. Weinberg showed that life cannot exist in a world with too much vacuum energy, and the same is true for a world with too heavy elementary particles. Perhaps the solution to the Higgs mass problem lies not in supersymmetry, but in a huge variety of landscape and anthropic need for a small value of this mass. For several years, we will be able to find out whether supersymmetry is really waiting for us "around the corner" or whether it is a mirage that constantly retreats as we approach.

    One of the questions that it is indecent to ask theorists is this: “If supersymmetry is so wonderful, elegant and mathematically perfect, why is the world not supersymmetric? Why don't we live in such an elegant universe that string theorists love most in the world? ”Could the reason be the anthropic principle?

    The greatest threat to life in a perfectly supersymmetric Universe does not come from cosmology, but rather from chemistry. In a supersymmetric Universe, each fermion has a twin-boson of exactly the same mass - this is the problem. Its culprits are the electron and photon superpartners. These two particles, called the electron (ugh, break the tongue!) And Photino, enter into a conspiracy to destroy all the usual atoms.

    Take a carbon atom. The chemical properties of carbon are mainly determined by its valence electrons - the most weakly bound electrons of the outer shell. But in a supersymmetric world, an external electron can emit photino and turn into an electron. The massless photino flies away at the speed of light, leaving the electron to replace an ordinary electron in an atom. And this is a big problem: the electron, being a boson, does not obey the Pauli exclusion principle and falls on the lowest orbit. In a very short time, all electrons will become electrons and will be in the lowest orbit. Goodbye, chemical properties of carbon, farewell to all other molecules necessary for life! The supersymmetric world can be very elegant, but it is not capable of supporting life — at least the kind of life we ​​know.

    Returning to http://arXiv.org website, you will find there two more archives: General Relativity and Quantum Cosmology (General Relativity and Quantum Cosmology) and Astrophysics (Astrophysics). In the articles published in these sections, supersymmetry plays a less noticeable role. Why should a cosmologist pay any attention to supersymmetry if the world is not supersymmetric? The answer may be Bill Clinton's altered phrase: “This is the Landscape, idiot!” 1 Although the symmetry can be partially broken, to a greater or lesser extent, in our little home valley, this does not mean that the symmetry is broken in all corners of the Landscape. That part of the string theory landscape that we best studied is the region where supersymmetry is exact and unbroken. The space, called the supersymmetric moduli space (or supermodule space), represents a part of the landscape, where each fermion has its own boson and each boson has its own fermion. As a result, the vacuum energy is strictly zero in the whole supermodule space. Topographically, this means that this part of the landscape is a flat plain, lying at zero height. Much of what we know about string theory is based on our 35 years of experience exploring this plain. Of course, this also means that some pockets of Megaversum must be supersymmetric. But not a single superstring theorist could enjoy life in one of these pockets. that this part of the landscape is a flat plain, lying at zero height. Much of what we know about string theory is based on our 35 years of experience exploring this plain. Of course, this also means that some pockets of Megaversum must be supersymmetric. But not a single superstring theorist could enjoy life in one of these pockets. that this part of the landscape is a flat plain, lying at zero height. Much of what we know about string theory is based on our 35 years of experience exploring this plain. Of course, this also means that some pockets of Megaversum must be supersymmetric. But not a single superstring theorist could enjoy life in one of these pockets.

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