Dark matter, dark energy and the fate of the universe - a chapter from the new book "Journey to the Dawn of the Universe"

The book is about the search for the elusive particles in the particle accelerator at CERN.

The book "Journey to the Dawn of the Universe" by Amir Axel was published by Aryeh Nir. From English: Emmanuel Lotem.

Where did we come from, what are we made of and where are we headed? What happened in the big bang?
The Large Hadron Collider is the most powerful machine ever built. This daring project by CERN, the European Organization for Nuclear Research, aims to recreate in its ring tunnel, which is 26.5 km long, the conditions of enormous heat and density that prevailed approximately 13.7 billion years ago, in the first fractions of a second after the birth of the universe in the Big Bang.
Today there is a generator that accelerates proton collisions at a speed of 99.9999991% of the speed of light, an incredible feat that has never been achieved before. With the help of the big accelerator, the scientists hope to identify the most elementary particles that make up the matter in the universe, understand the laws that underlie all the forces of nature - and perhaps even solve the riddle of creation.

How many dimensions does the universe have? Is there such a thing as an "anti-universe", and if there isn't, where did the "anti-universe" go?
Amir Axel leads us into the control rooms of Tsaran at key moments and introduces us to the international team of scientists who strive to fulfill the cautious hopes that were placed on the accelerator. Excel explains the scientific concepts necessary to evaluate the future discoveries to come from this great machine when it is operated at full power. For the purpose of writing the book, Axel interviewed thirteen Nobel laureates in physics and many other scientists - physicists, cosmologists and mathematicians - and with their help he leads us on a fascinating journey of discovery about an event that has the power to change our perception of the world.

What is the nature of the dark matter that fills the galaxies? Is there a danger that the accelerator's activity will create a black hole that will swallow our world?

The journey to the dawn of the universe, Present at the Creation, penned by one of the best popular commentators of science living with us today, allows us to trace the course of the most wonderful experiment in the history of science, which promises to fulfill Einstein's request, "I want to know what God was thinking about - Everything else is details."

Dr. Amir D. Aczel is a researcher of the history of science at Boston University. He authored fifteen non-fiction books, including "The Riddle of the Compass" published by Aryeh Nir, as well as the book Fermat's Last Theorem: Unlocking the Secret of an Ancient Mathematical Problem, which was translated into 22 languages.

11

Dark matter, dark energy and the fate of the universe

Einstein's theory of general relativity is, in the eyes of many, a model for a perfect physical theory: Einstein's equations contain the virtue that physicists call beauty, or elegance. What does this mean?
Einstein's theory describes an extremely complex spatiotemporal reality, with astonishingly limited equations, and with a minimal number of parameters. Because of this, the theory is in line with the principle called "Occam's Razor": the simplest theory has the best chance of being proven correct. Or as Einstein put it, in a famous expression, a theory should be "as simple as possible, but no more than that".
It also has a tremendous and all-embracing symmetry of space - the professional term is general covariance - which assumes that the laws of physics do not depend on the coordinate system we use to specify space and time, whatever it may be. If we take an ideal city for example, the distance between 34th Street and the corner of Second Avenue and 19th Street and the corner of Fourth Avenue should not depend on the labels we use to mark the streets and avenues (assuming that they cross at right angles, and that the intervals between them are equal). The logic of Einstein's model is based on this symmetry, and it is what gives it its elegance; And it is also necessary for explaining the laws of physics. Following Einstein, the idea of ​​elegance took on a life of its own in physics, not only because it produces aesthetically pleasing equations, but also because elegance seems to act as a tool for explaining nature. Equations that are pleasing to the eye, are often also true: nature loves beauty.
The success of the next great model of physics, the standard model - another theory based on the concept of symmetry - spurred physicists to look for more mathematically and aesthetically pleasing models, with a deep belief that such models have a good chance of proving to be correct in the description of nature. And yet, does nature always adhere to these principles? In this chapter and the one following it, we will learn about some relatively new physical theories - they were developed mainly in the last third of the twentieth century (although their roots go back to earlier decades of the same century) - which are considered beautiful, fascinating and fun, in the eyes of those who peruse them and develop them further. But not one of these theories has so far found a shred of reinforcement in the form of experimental evidence.
On the other hand, there are physical phenomena that we have so far been unable to explain. Therefore, there is a strong need to strive to match the elegant models with the unexplained phenomena, and physicists hope that at least some of these mysteries will be solved by one or more of these beautiful new theories. It is possible that the highest test of some (at least) of these models will be in the third grade.
Since the XNUMXs we have known that the universe is expanding, but not much was known about the change in the speed of expansion over cosmic time. Many physicists assumed that since gravity extends infinitely in space, the mutual attraction of all the mass in the universe should eventually slow down the expansion that began with the big bang, so that the universe will return and collapse in on itself at some point in the distant future. Then maybe another big bang will occur, as part of a perpetual cycle of birth, death and rebirth.
But in 1998, this optimistic philosophy of a constantly regenerating nature was shattered. Two teams of astronomers, one at Berkeley led by Saul Perlmutter and the other at Harvard led by Robert Kirchner, have separately announced surprising discoveries found in the study of the rate of receding of very distant galaxies. The researchers reported that the expansion of the universe is not slowing down at all, but rather is accelerating. This means that unless some force miraculously intervenes to somehow overcome the acceleration, the expansion of the universe will continue forever. Eventually, in the very distant future, the universe will become extremely sparse, and die after all the stars have exhausted their nuclear fuel.
These findings caused a scientific sensation - no one expected them. Later, the mathematical catalyst of the accelerated expansion was identified, in the form of a long-abandoned constant - the cosmological constant (denoted by the Greek letter lambda) which Einstein used for the first time in the model of the universe he built in 1917. He did this because his model of the universe tended to expand, while the astronomers of those days told him that the universe was static. That's why Einstein added the element for matter to his equations, to prevent the universe from expanding - and thus missed the opportunity to theoretically predict the expansion of the universe...
When Einstein learned in 1929 that Vesto Sleeper, Edwin Hubble and Milton Humson had discovered that the universe was indeed expanding, he threw Madda away as a useless tool and exclaimed: "Then eliminate the order of the cosmological constant!" The irony of fate is that a model of an accelerating universe requires the use of learning in the Einstein equation, except that from now on its function is not to prevent the expansion of the universe, but rather to accelerate it.
If Meda is the model for the force responsible for accelerating the expansion of the universe or not, scientists have not been able to identify the force in question. The inevitable conclusion is that there must be some unknown and mysterious form of energy that fills all space - there must be something, at all ends of space, a kind of shadow force, that constantly "pushes" the very fabric of space-time, overcomes the force of gravity and repels the The space to the "outside". It is a strange kind of force that cannot be seen or felt, except in its action to accelerate the expansion of the universe. This invisible energy is called dark energy.
The discovery of dark energy once again put another mystery concerning the universe as a whole on the agenda, which scientists have wondered about since it was discovered in 1933 by the Swiss-American astronomer Fritz Zwicky of the California Institute of Technology. After a careful study of the collective gravitational pull exerted by galaxies on their own stars and on other galaxies in their clusters, Zwicky reached an inescapable conclusion: things do not add up correctly. The masses of the galaxies, calculated according to the number of stars and the amount of dust in them, do not even begin to approach the size necessary to prevent the disintegration of the galaxies as they rotate around themselves! His conclusion was that the universe must contain much more mass than we can see in our telescopes. This mysterious missing mass is now called dark matter.
All the astronomical research that was conducted in the years that followed, with telescopes of ever-increasing power and analysis methods whose power also increased in a similar manner, failed to resolve the problem of this stubborn gap discovered by Zwicky, between the total amount of visible mass and the total amount of mass as calculated based on gravity The collective gravity of the galaxies. Well, where is all this missing mass of the universe? Until now, dark matter has been identified solely by its strong gravitational influence on ordinary matter. Apparently, it is not involved in electromagnetic interactions at all, unlike normal matter. We don't see it and we don't feel it - but we know it exists, because it is necessary to balance all the gravitational forces necessary to hold the stars and galaxies in their places.
Today, scientists believe that no less than 96 percent of the total mass-energy of the universe (the two are equal according to Einstein's formula, as you remember) is dark: 73 percent is dark energy; 23 percent is dark matter; And almost all of the remaining four percent of mass-energy is dust and gas. Only an amount of 0.4 percent of all the mass and energy of the universe exists in the form of light-emitting stars. In other words, dark matter makes up 85 percent, no less, of all matter in the universe.
The calculations show that there is not much chance that the dark matter is hiding in black holes, or that it can be explained by means of neutrinos, those particles that are found in such great abundance, that hardly interact with other matter. Their total mass does not amount to a number close at all to the missing amount. At present, no one knows anything about the nature of this vast amount of missing matter in our universe.
Today, scientists attach great importance to this pair of mysteries of the mass-energy of the universe - dark matter and dark energy - because these mysteries have so far stood in the way of all our attempts to investigate. Therefore, a search is underway to find candidates for the role of dark matter, which makes up almost a quarter of everything in our universe, and to try to explain dark energy. The need to solve these puzzles mobilized the particle physicists - the experts in the study of the very small things - to the help of the astronomers, the astrophysicists and the cosmologists, all of their efforts to provide answers to these two problems in the realm of the very large things have been thwarted until now. The particle physicists have accepted the challenge, and now they are trying to explore the physics beyond the standard model in search of solutions.
In their search for candidates for the role of dark matter, physicists have come up with many possibilities, among them exotic matter: strange particles, the fruit of the imagination, rather than entities based on something we can see in the physical world around us. Some of the possible dark matter candidates proposed by physicists are so mysterious that they don't have names, and are marked with letters like "D" (for dark) or "X" (for "disappeared"), or with nicknames like "Q-balls" (lumps formless of matter), axions or saxions. For now, these exotic beings exist only in the imagination; But if this kind of strange material is detected in the HG experiments, there is no doubt that it will change our views on the structure of the universe.
Some physicists have raised the possibility that dark matter will become visible to us through its interactions: if a dark matter particle collides with a dark matter antiparticle, energy may be released that we can detect. As described above, the Pamela satellite (a somewhat forced acronym for "useful payload for antimatter-matter research and the astrophysics of light nuclei"), launched in 2006 by a consortium of European scientists, searches for antimatter in space. He is also looking for evidence of this exact type of interaction - the ionization of dark matter particles when they come into contact with dark matter antiparticles.
According to Gordon Kane, a senior particle physicist at the University of Michigan, the latest Pamela data are consistent with such ionization processes, and may provide indirect evidence to support the existence of dark matter.

The greatest hope that depends on the results of the HG, after the discovery of the Higgs, is the help of the accelerator in identifying part of the missing mass of the universe by discovering a new group of particles, the existence of which is predicted by a theory of a certain type that extends the symmetry of the standard model - or perhaps even several groups of particles such

The existing symmetries within the group of quarks gave rise to quantum chromodynamics and predicted the existence of new particles; The lepton symmetries provided the unified electroweak force of Weinberg, Salam, and Glasho; And combining three types of symmetry created the complete standard model. Therefore, against the background of the great successes of the idea of ​​symmetry in nature, some physicists began to wonder if it is possible to expand this idea further. In particular, is it possible to increase the symmetry of the standard model so that it creates a direct connection between additional particles, and therefore predicts the existence of "new" particles?

See the following three groupings:

Quarks to photons

bosons

Physicists considered two directions for expanding the standard model. One approach tries to find a symmetry that will bring the quarks together with the leptons; The other asks for a symmetry that connects all the fermions - quarks and leptons - with the bosons.

In 1974, Abdus Salam and his colleague Jogesh Patti wrote an article that claimed that it was possible to expand the color charge of the quarks to four colors, instead of the usual three, and that the fourth color would allow the inclusion of leptons in the quark model. At about the same time, Sheldon Gelshaw and Howard Giorgi at Harvard began to search for a Young-Mills symmetry gauge group that would allow them to mathematically unify all quarks and leptons into a single model. The two found a new and large Lee bunch, which contains the standard model within it, and also links the quarks and leptons in a single symmetry. Physicists call such an approach a grand unified theory. But don't let the word "big" mislead you - the theory is big in a rather limited sense: it unites the quarks with the leptons. Georgi and Glasho's model was the first grand unified theory.

An important implication of the grand unified theories is the possibility of quarks turning into leptons. In particular, this type of theory implies that the proton will eventually decay into a lepton (having a positive electric charge and therefore, according to the law of conservation of charge, it must be an antiparticle). This particular interaction has a grim implication for the future of the universe: given enough time, all the hadronic matter in the universe will disappear! If the theory is correct, then in the very distant future the protons will disintegrate, the nuclei will disintegrate as a result, and at the end of the process there will be no atoms left in the universe - only individual electrons, positrons and neutrinos, flying to them in an ever-expanding empty space.

But the decay of the proton has never been observed experimentally, although scientists have been looking for it for many years, in observations of large containers of pure water buried in the earth's crust, aiming to detect radiation in them that has no other explanation. The Super-Kamiokande project in Japan is trying to track proton decay, apart from neutrino oscillations. Scientists working on the project reported not long ago that if there is indeed a proton decay, then it should occur after a period of time of at least 8.2 × 1033 years (the previous estimate was at least 1032 years). That is, we do not need to fear such a breakdown in the near future.

At the moment we do not know if the proton may decay, because the evidence for this process is only theoretical, and depends on a mathematical model that has special assumptions that have not been put to the test. Speculation regarding the possibility of the decay of the seemingly very stable proton has been floating in the air for many years. Maurice Goldhaber, who headed Brookhaven Laboratory and who hoped to witness the discovery of proton decay in an experiment, said already twenty-five years ago: "If only the proton would live forever! But if he is mortal, who will let him die by my hands..."

The second way physicists are testing to expand the standard model is the aspiration to embrace the bosons and fermions in a single symmetry group. This idea is called supersymmetry - it is a symmetry greater than that of the standard model, which contains it as a subgroup. The initials of supersymmetry in English are SUSY, so some call it "Suzy".

The idea of ​​hypersymmetry was developed in the Soviet Union in the seventies, but many years passed before the work of the Russians became known in the West. In 1971 Yuri Golfand and Yevgeny Lichtman began the construction of a supersymmetric field theory, and two years later another pair of Russian physicists, Dmitry Volkov and Vladimir Okulov, found the first theoretical breaking of supersymmetry. Without knowing anything about the Russians (who also knew nothing about him), the Italian physicist Bruno Cumino, now professor emeritus at the University of California at Berkeley, with his late Austrian colleague Julius Wess, developed the idea of ​​supersymmetry at about the same time.

Julius Ves studied at the University of Vienna, where he was greatly influenced by Erwin Schrödinger. Bruno Tsumino was already a professor when he first met Ves, when Hela was just a research student. The two began working together on symmetries in physics, and built a model of nature that is considered particularly elegant by many physicists today. Some call him "the beautiful Susie".
In one of her first theoretical successes, Susie solved the problem of the great difference between the orders of magnitude of the four forces of nature. As described above, according to the standard model the three forces it deals with do not meet at one exact point in the distant past, right after the big bang; But under supersymmetry they manage to do so. And it's even possible that gravity, with an exception to the even more distant past, might also coalesce with the other three forces.

Since three of the forces of nature (and maybe four, according to certain assumptions) come together under a supersymmetry at the beginning of the universe, the supersymmetry suggests a unification of the forces. In this view, the forces go their separate ways only after the universe began to cool, and the original symmetries were spontaneously broken; But if we use the Suzy model, we can see that there used to be a great symmetry. This unification at the beginning of time, which was followed by symmetry breaking, gives the model a great deal of elegance as a theory that ties together all the forces, roughly at the time of their formation.
Another great advantage of supersymmetry is that this theory behaves very well on the theoretical level. There is no need to do a lot of renormalization work, that is, it is easier to eliminate infinite values ​​from its solutions, than to do it within the framework of the standard model.
Two weeks before his death in 2007, Julius Ves spoke at a conference on supersymmetry, SUSY07, held that year at the University of Karlsruhe in Germany. He had high hopes for the MHA's entry into action, which was then supposed to begin in 2008. Unfortunately, Ves didn't get to see if the HC would verify his theory and that of his vows. In his lecture at the conference, Vess emphasized the idea of ​​symmetry and explained how he and his followers led him to hypersymmetry:

Everyone notices symmetry, one way or another. I think it's worth mentioning that about thirty years ago, there was a lot of interest in great apes, with the aim of seeing how much they were able to learn. One of the goals was to see how apes would learn to draw. In one of these experiments, a dot was drawn on one side of a sheet of paper, and then the experimental animal tried to draw a dot on the other side to create a symmetrical balance. This is exactly what we do in physics.

The idea behind "Susie" is that every boson has a partner fermion - another point drawn symmetrically on the other side of the sheet, so to speak. And to the same extent, every fermion has a companion boson. These are called super partners. But since the numbers of fermions and bosons are not equal, it is necessary to "invent" more particles and add them to the model, in order to bring about a complete match between the two groups. Some of the yet-to-be-identified particles necessary for this model are excellent candidates for the role of dark matter.

The calibration bosons of the standard model have common fermions in the supersymmetric world. These are collectively called "gaijinos" ["chiolins"]. For example, a gluon has a superpartner called a gluino; The W boson's superpartner is the Wino. The chargino [“our charges”] is a charged particle that is a quantum mixture of particles; And the neutralino is a neutral particle that is also a quantum mixture. As we saw in our discussion of neutrinos, the suffix "-ino" is the diminutive form in Italian (a cell phone is called telefonino in Italian), and it seems that this is the source of this method of naming - perhaps as an extension of the idea of ​​Fermi, who gave the neutrino its name. And as you might have guessed, the superpartner of the Higgs is the Higgsino.

Other superpartners are given names starting with the letter S: there are sleptons and there are squarks - these are the superpartners of the standard model's leptons and quarks. In more detail, the superpartner of the bottom quark [bottom] is the subatom; The super partner of the top quark [top] is the stop; And in the Slaptones sector, there is for example the Stauon. According to one theory, the quarks and the gluons are perhaps the heaviest superparticles.
In the family of models based on "Suzy", some of its members are closer to the standard model, while others among its members are more detailed, and therefore further away from it. The supersymmetric model that is most similar to the standard model of particle physics is called the minimal supersymmetric standard model, abbreviated as MSSM. This is a powerful theoretical structure in modern physics, and many believe in it and are engaged in its development. Its limitation is the poor chance it offers for explaining a significant part of the missing matter of the universe. Another model is called NMSSM - the post-minimal supersymmetric standard model. Both of these are fairly minimalistic extensions of the Standard Model, and both include candidates for new particle roles, which may be verified by collisions from the HG. But the more complicated supersymmetric models need much higher energy levels of the particle beams, in order to allow the phenomena they predict to be observed, and therefore these theories have fewer chances of being verified than the GHG. And at even higher energy levels we find the string theory models, which will be described in Chapter 12.

The problem of dark matter oppresses physicists, and it is therefore no wonder that with the opening of the HG experiments, the eagerness to discover the source of dark matter does not fall short of the eagerness to discover the Higgs particle. Since the supersymmetric partners - even if they are discovered - are not expected to add to the aggregate mass of all particles known to the standard model the amount necessary to fully fill the gap, scientists have been found who have come up with even more extreme theories.

In several very high-level scientific conferences held on the eve of the opening of the MHC, physicists working at the cutting edge of particle physics presented ways in which supersymmetry could be verified using the large hadron collider accelerator. Below I will describe in some detail the theories presented at these conferences, just to give you an idea of ​​the nature of the most advanced research in theoretical particle physics and the richness of the work of the senior researchers.
The graviton is the supposed boson that mediates the action of gravity. He was never seen on the lookout. If the graviton exists, then according to the theory it should have spin 2. As you remember, the W and Z bosons, the photon and the gluon have spin 1, while the Higgs, if it exists, has spin 0.
There is a theory called supergravity, which is an extension of supersymmetry that includes gravity. This theory predicts the existence of the gravitino: a superpartner of the graviton, which is an analogue of the superpartners of the standard model bosons W and Z. According to a recent estimate, the gravitino may be a good candidate for the role of dark matter. "It is possible that gravitino is a natural candidate for dark matter. But we have no idea what its mass might be," said Wilfried Buchmiller of Hamburg, in a presentation on supersymmetry at the SUSY09 conference in Boston.

According to some, another excellent candidate for the role of the dark matter particle in the framework of the supersymmetry theory is the gluino. As you remember, this particle is the analogue, in the world of supersymmetry, of the gluon in our world. According to the physicists, it will be possible to identify gloins by their decay into hadronic jets and staunons.

Whereas, according to Raman Sundrum of Johns Hopkins University, nature has a "dark sector" with its own "dark particles", completely separate from the supersymmetric partners that collectively belong to the "Suzy sector" of his model, and this sector, in turn, is completely separate from The standard model". There is a "dark force" that operates in the "dark sector", and the photons of the "dark sector" are "dark photons". The logic behind Sondrum's "dark model" is what he calls "dark matter observations" - the interpretation he gives to some recent scientific reports. These "sightings" are unexplained phenomena recorded by research satellites, and Syndrom equates them to "UFO sightings", no less and no more...

Besides all these components, Sondrum's model also includes a component of string theory called Roman (abbreviation of the word "membranous", membrane), on which the various sectors depend. In his model there is also a hidden sector that lives in its own space, and is connected to the rest of the model through a fifth dimension (high dimension) "coiled" of space-time, the existence of which is required by string theory. Gravity mediates all interactions between the sectors, because dark matter reveals its existence only through its gravitational effects. Sondrum's model also includes a "dark Higgs sector", which gives mass to the dark photon. The supersymmetric model, the standard model and supergravity mediate between the hidden sector and the dark sector, which are separate from each other. Needless to say, this model is difficult to digest, even for those physicists who are already used to very strange models of the universe. And of course, there is no chance for such a cumbersome and complicated model to pass Einstein's test of elegance; But it is there to give you an idea of ​​the nature of the models of the universe that some of the physicists working today are thinking about.

You don't need to conclude from all of the above that supersymmetry was developed to solve the dark matter problem. The supersymmetry is an elegant extension of the ideas of the standard model, which was derived - based on theoretical considerations only - by talented physicists who devoted themselves heart and soul to the idea of ​​symmetry and tried to expand it further and further. But chance would have it, and the supersymmetry necessitates the existence of many types of particles than what we know today, therefore it holds the promise of solving the dark matter problem. Furthermore, it contains the fiercely tempting hope for the unification of the forces of nature at the very high energy level that characterized the time period immediately after the big bang, and it even offers, as a bonus, a relatively convenient possibility for renormalization.

Sondrome's tangled and complicated model makes use not only of symmetry, but also of ideas from string theory. In terms of historical development, there is a connection between these two theories, string theory and supersymmetry: in fact, supersymmetry drew its inspiration from the first ideas put forward in the study of strings. Both supergravity - the supersymmetric model that includes gravity - and string theory aim to merge Einstein's general theory of relativity with quantum field theory.

In the last twenty years, string theory has become one of the most important theories in physics, because it is considered elegant and has a lot of theoretical unifying power, and these two aspects have attracted bright young physicists in droves. We will now discuss this theory.