The Universe Before the Big Bang The Cosmological Background of Gravitational Radiation (P3) Amongst all those alternative backgrounds, a very intense one could be associated with the gravitational radiation produced by what are known as topological defects, i.e., geometric configurations characterized by particular symmetry properties: spherical symmetry for monopoles, cylindrical symmetry for cosmic strings, planar … Read more
The Universe Before the Big Bang The Cosmological Background of Gravitational Radiation (P1) There exist a number of physical effects characterizing the various models of the primordial Universe, and allowing us to discriminate between the different scenarios. All these effects are linked more or less directly to the radiation production which characterizes the transition from … Read more
The Universe Before the Big Bang Inflation and the Birth of the Universe Finally, the reader may ask why the phase of pre-Big-Bang inflation has been represented in Fig. 5.3 by plotting two different types of behavior of the spatial radius, corresponding to the solid curves labeled by R (the inner one) and RE (the … Read more
The Universe Before the Big Bang Inflation and the Birth of the Universe The standard cosmological model, which describes the current Universe in terms of its matter and radiation components, and covers a seemingly long period of time – more than 10 billion years, from epochs preceding the synthesis of nuclear elements until now – … Read more
The Universe Before the Big Bang The Theory of Strings Hence, the observed processes can be suitably described by applying the formalism of quantum field theory following the standard model of elementary particle physics, without any reference to string theory. The same conclusion applies to the gravitational force if we limit ourselves to sufficiently flat … Read more
The Universe Before the Big Bang The Theory of Strings This chapter is devoted to those readers interested in the physical foundations of pre-Big-Bang cosmology and who wish to learn the basic concepts of the theory of one-dimensional extended objects – usually dubbed string theory. In particular, we will try to outline here the quantum … Read more
The Universe Before the Big Bang String Theory, Duality, and the Primordial Universe For anybody reading the introduction, there will no doubt have been important questions which arise spontaneously and are left unanswered. For instance, why does what we have called the “pre- Big Bang scenario” emerge within string theory and not within the classical … Read more
The Universe Before the Big Bang String Theory, Duality, and the Primordial Universe After this discussion, it is probably more evident to the reader why the existence of cosmological solutions that expand with increasing curvature is a peculiar property of string theory: the appearance of these solutions, as well as their close link to the … Read more
The Universe Before the Big Bang: General Relativity and Standard Cosmology The physical description of the current Universe, and of the forces that stars, galaxies, and clusters of galaxies exert upon one another at the cosmic distance scales corresponding to their huge spatial separations, requires the use of general relativity, i.e., Einstein’s gravitational theory. Some may … Read more
The Universe Before the Big Bang: General Relativity and Standard Cosmology Exploiting these assumptions (which may appear rather an oversimplification, but which are supported by various direct and indirect observations), one can exactly solve the Einstein gravitational equations, thus determining the evolution of the cosmic geometry and its gravitational sources. One then finds that the energy … Read more
