by Marina KHALIZEVA, journalist
Today astronomy has become a center of gravity of scientific discoveries. For centuries, it was considered the most conservative field of knowledge, but impressive achievements of the last decades have changed this standpoint. What is the crux of recent cosmological breakthroughs, how do they change our perception of the Universe and what should we know about it, how the Large Hadron Collider—the biggest experimental unit in the world built in a quiet suburb of Swiss Geneva-will contribute to these "modest aspirations"? Academician Valery Rubakov, who in May 2010 delivered a lecture at a joint seminar of scientists working on the CMS detector of the European collider organized at the RAS Institute for Nuclear Research (Moscow), answered these questions.
This lecture, supposed to be an ordinary event, turned out a real success. Among those who attended the lecture of Rubakov, a recognized specialist in the quantum theory of the field, particle physics and cosmology, Professor of the Department of Physics at the Lomonosov Moscow State University, chief scientific assistant of the Theoretical Physics Department at the Institute for Nuclear Research, and finally, the youngest RAS academician (elected in 1997 at the age of 42), were not only his close colleagues. The organizers arranged video broadcasting of the lecture, which enabled employees of the European Center for Nuclear Research (Switzerland), scientists from Novosibirsk, Tomsk, Omsk, Dubna, Gatchina and other Russian science towns to virtually attend the lecture.
According to the lecturer, cosmology has become an exact science recently. Scientists are obtaining quantitative data that characterize both modern state of the Universe and its evolution right from the first seconds after the Big Bang. Based on these data, scientists made a general conclusion: the available information on the fundamental particles and interrelations between them, forming basis of the Standard Model, is insufficient to describe the world we live in, and this theoretical con-
struction requires further development. Generally speaking, experiments at the Large Hadron Collider will help to "expand" these limits and finally understand how "the nature is organized"*.
The presence of matter and almost complete absence of antimatter in the Universe is the first historical evidence of our poor knowledge of the physics of the microworld. Rubakov pointed out that such asymmetry between matter and antimatter is really strange, as there was an epoch in the early Universe when the processes of pair creation and annihilation (conversion) of particles and antiparticles took place. At that time (measured by split seconds from the Big Bang), the Universe was filled with them, besides, a billion pairs of particles and antiparticles accounted for one "extra" particle. Later on, during expansion and cooling of the Universe, antiparticles annihilated with particles, "odd" particles remained and formed the matter around us. The question of how there was an asymmetry between matter and antimatter formed, was posed as early as in late 1960s by Academician Andrei Sakharov and RAS Corresponding Member Vadim Kuzmin, but it has no simple answer.
Perhaps, a key to this problem has been recently discovered in the form of transmutations (oscillations) of neutrino—the lightest particles that hardly interact with matter. The Russian-American experiment SAGE, conducted from 1990 to 2000 at the Baksan neutrino laboratory (RAS Institute for Nuclear Research) located in one of the canyons of Northern Caucasus (the Kabardino-Balkarian Republic), contributed a lot to this achievement.
Neutrino oscillations are the first phenomenon beyond the framework of the Standard Model, discovered during ground experiments. According to Rubakov, it means that laws of conservation characteristic for the theory of elementary particles are in fact being violated, which, conceptually, is enough to explain imbalance between matter and antimatter in the Universe. Further discoveries in this field of knowledge are connected with the creation of new neutrino detectors, artificial neutrino sources, measurement of their mass, experiments conducted on nuclear reactors and powerful accelerators. This is where the Geneva unit appears on the stage.
The other evidence of the necessity to radically expand our knowledge of microphysics is connected with the composition of the modern Universe. According to the cosmological data, only 5 percent of its mass is a regular matter, 0.3-3 percent are neutrinos. As for the rest, its composition is "unknown" and, according to Rubakov, consists of two fractions—dark matter (about 25 percent) and dark energy (65-70 percent)**.
Dark matter present in the galaxies and their conglomerations is able to thicken. The lecturer believes that it is composed of unknown particles that are heavier than proton 100-1,000 times. In general, we can say that the existence of this dark mass gives life to a new category of physical phenomena occurring at supershort distances. It can be studied by way of registration of dark matter particles in the course of underground low background experiments, their direct production in the
* See: L. Smirnova, "Start of the Large Hadron Collider", in this issue of our magazine. -Ed.
** See: "Dark Matter Puzzle", Science in Russia, No. 1, 2010.—Ed.
course of experiments on accelerators and detection of products resulting from their annihilation. All this is a primary task of the Large Hadron Collider.
Russian physicists play a significant role in these studies: some secrets have already been disclosed by means of the Baikal neutrino telescope (RAS Institute for Nuclear Research), located in the lake at a depth of 1.366 m. There scientists are trying to produce neutrino high energies, which form in the course of annihilation of dark matter particles in the center of the Earth or the Sun. Further development of this underwater unit, connected with an increase of telescope capacity, will help understand dynamics of astrophysical processes.
Unlike dark mass, dark energy is evenly "spread" in space and is characterized by extraordinary properties. Observation data show: today the Universe is rapidly expanding, i.e. dark energy in some sense is affected by antigravity (which, by the way, does not contradict to the general relativity theory). But its nature, according to Rubakov, is, perhaps, the main scientific mystery of the 21st century.
Deep interrelation between physics of particles and cosmology is also proved by the inflation theory of the Universe. It was put forward in late 1970s-early 1980s by famous scientists Alexei Starobinsky, Andrei Linde (USSR) and Alan Guth (USA) and gives answers to global questions: Why is the Universe so big and homogeneous? Why is our three-dimensional space Euclidean (named in honor of the ancient Greek mathematician Euclid, who lived in the 3rd century B.C.), i.e. is not bent? According to the model proposed by theoreticians, at an early stage of evolution, the Universe expanded with great acceleration: from micro- to macrosizes in split seconds. This theory also explains cases of primary inhomogeneities, which consequently lead to the formation of stars, galaxies and their conglomerations, as a result of strengthening of quantum fluctuations of fields in vacuum. Such picture, according to Rubakov, is easily compatible with the available cosmological data, and its final acknowledgement depends on future measurements of relict radiation.
The Universe extension mechanism is closely connected with the processes taking place at supershort distances and ultra-high energies, which at the moment cannot be studied experimentally. Most probable prospects here are connected with the Geneva accelerator, scientists are planning to use to get colliding beams of protons with energies of 7 TeV.
In conclusion, Rubakov pointed out that recent discoveries in cosmology and particle physics decisively prove: we have entered a new phase of crucial changes in our opinion of the nature. Experiments to be conducted on the Large Hadron Collider will enable us to look deeper into the riddles of the Universe. Probably they will confirm or disprove a part of the theories and conjectures presented by the scientists. And this means that answers to the fundamental questions of modern physics—how did the Universe behave in the first seconds of its existence? how did particles gain mass initially? why does antimatter differ from matter?—are still ahead.
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