Sky & Telescope March 1983 [antikvár]

The Inflationary Universe Lives?WHAT AN ASTRONOMER means when talking about the "early universe" will depend on individual interests and prejudices. To some it means the era during which galaxies formed, beginning perhaps 10 million years after the Big Bang. For others, it is the period of helium synthesis a few minutes after the formation of the universe. But to those scientists who are interested in the overlap between particle physics and cosmology, the universe was already suffering from senility by then. These individuals are concerned with events that occurred in the first fraction of a second after the creation of the universe.It may seem strange that there should be any connection between the large-scale structure of the universe and the sub-microscopic world of elementary particles. However, recent developments in both fields have shown that they are intimately related. As a result of these discoveries, a radically new picture of the "early universe" has been developed.GRAND UNIFIED THEORIESPhysicists have always wondered why the four forces controlling the universe gravitational, electromagnetic, and the strong and weak nuclear have such different strengths and properties. For example, the dominant force in the universe appears to be gravity, but it is in fact 39 powers of 10 less powerful than the strong nuclear interaction that holds atomic nuclei together.In the last decade this question has been partly answered. Physicists have had great success in finding a mathematical description that unifies the electromagnetic and weak forces. Theory predicts that, even though these two interactions are apparently very different, at high enough energies they become identical. The energy required, about 10'^ electron volts per particle, is just within reach of the latest generation of accelerators. It should soon be possible, therefore, to test these ideas experimentally.Spurred on by these successes, Grand Unified Theories (GUT's), combining the electromagnetic-weak and strong nuclear forces, have been proposed. They predict that above a certain definite energy there exists a state known as the symmetric vacuum.- In this regime the behavior and properties of the nongravhational forces of nature are identical. Below the critical value the universe is asymmetric as we see it today. In other words, the unified or symmetric properties of the forces that control much of the universe are not observed in processes occurring with energies below a certain threshold value.Unfortunately for experimentalists, thetransition from one state to the other, achieved by a process called spontaneous symmetry breaking, does not occur until the energy of the system exceeds 10" eV per particle far beyond the capabilities of any conceivable accelerator. (However, GUT's predict that the proton is not stable and will have a half-life of about 10'° years. The technology exists to verify this experimentally, and several teams of researchers are at present carrying out the relevant measurements.) Indeed, the only place such colossal particle energies could have been achieved was immediately after the Big Bang, when the universe was only 10"" second old.One of the ways to test these ideas is to see if any of the observed properties of the cosmos today are a consequence of the early symmetry. Long-standing problems that seem to find solutions within this new framework include the apparent absence of antimatter in the universe, and the disparity between the number of particles of light (photons) and particles of matter.DEATH OF THE STANDARD BIG BANG?Cosmologists have been using the framework provided by these Grand Unified Theories to gain a deeper insight into the structure and history of the universe. But, in the process, they have encountered a number of problems. For one thing, vast numbers of magnetic monopoles should have been produced during the Big Bang. Although there is some evidence that these isolated magnetic "poles" exist (see page 336 of the October, 1982, issue), theory predicts that their total mass would be so great that the expansion of the universe would have stopped and reversed long ago.In addition, the union of these diverse theories spawns monsters such as "domain walls" and "vacuum strings," which are extremely stable large-scale structures generated from quantum fluctuations when the universe undergoes spontaneous symmetry breaking. A typical string would have a thickness of 10'" meter, a length ofIn this space-time diagram (with two of the three space dimensions left out for clarity), light rays from three points {A, B, and C at time Tq) move outward making 45 angles to the axes. The subsequent positions of A, B, and C are shown by the bold vertical lines. At time Ti, these points are not in causal contact: there has been insufficient time for light signals or anything else to traverse the distance between them. At time Tz, information from A and C first comes into contact with B. An observer located at point B will be able to look out into space (and therefore back into time) and be able, in principle, to see events occurring anywhere in his triangular blue region his so-called past light cone (the similar regions for observers A and C are also shown). On the other hand, an observer located at C will have to wait until time Tj to be able to detect events occurring at A.September, 1983. Sky & Telescope 189