Particle horizon

About: Particle horizon is a research topic. Over the lifetime, 2096 publications have been published within this topic receiving 69137 citations.

Elements of cosmology

Abstract: The fundamental force keeping solar systems, binary stars, and galaxies together is the force of gravity (as opposed to electric, magnetic, and nuclear forces), and it is not unreasonable to suppose that the force governing the large-scale motions of the entire universe is primarily gravitational. If there is some other force governing these motions, there has to date been no evidence for it, neither in the solar system, nor in the observable galaxies. By the universe we mean all detectable components in the sky: stars, galaxies, constellations, pulsars, quasars, as well as such things as cosmic rays and background radiation. If this directly observable universe is part of a much grander system of universe-within-universes (C.V.I. Charlier’s hypothesis1) then there is little we can say.

Full Causal Theory of Bulk Viscosity and Specific Entropy of the Universe

Abstract: This article deals with the full Israel–Stewart causal theory of bulk viscosity as employed to the dissipative expansion of the early universe. It is shown that the nontruncated full theory can be cast in the form of a noncausal theory with an auxiliary condition which states that the square of dissipative contribution to the speed of sound varies with the particle number in a comoving volume. Also, a generalized temperature appears in a cosmological invariant which is shown to hold good for the dissipative expansion in an intermediate brief transition period (around the epoch time α = 10−23 s) between the very early “mild inflation” stage of the universe and the standard radiation-dominated FRW era of it. With this generalized temperature, the Gibbs equation has been generalized. This equation is also shown to have an alternative form with a term depending on bulk viscosity. In the dissipative transition period, the universe as a thermodynamically open system of viscous fluid can generate specific entropy. In this period the temperature rose to a considerable extent. Due to the cosmological invariant, the dissipative contribution to the speed of sound and consequently the particle number decreased sharply, ensuring the second law of thermodynamics. It is possible to have an estimate of the specific entropy in consistency with the observations. The total entropy and the particle number of the observable universe have also been found here. These estimates agree with the accepted values for them.

A Cyclic Universe without Missing Mass: Implications of R->alpha'/R

Abstract: Results from string theory conclude that a spatial dimension R is equivalent to *'/R. If R is considered as a four-space dimension, several interesting results emerge. In this paradigm, *'/R exists in a time-reversed, "anti- parallel" universe. Cosmological distances in our real-time universe are equivalent to the compact dimensions at the instant of a Big Bang in a time- inverted universe. This model agrees with standard black hole theory in that particles become frozen in time when they reach the 'singularity' (of dimension alpha'). A particle which enters a black hole in real time exits from the Big Bang or "white hole" in the time-inverted universe, leaving behind a trace of annihilation radiation. A diagram of this phenomenon is constructed, consistent with existing knowledge of the early universe. The primordeal black holes predicted by Hawking are required. A cyclic universe is described by M^2\p,n + T^2 = 1. The "missing mass" proscribed by standard closed- universe theories is not required. This result is useful if experimental evidence in the search for dark matter continues to leave a significant "missing mass" - and particularly in light of more recent observations indicating that, in fact, inflation continues at a much reduced rate.

Conditions for spontaneous homogenization of the universe

Abstract: The present-day universe appears to be homogeneous on very-large scales. Yet when the casual structure of the early universe is considered, it becomes apparent that the early universe must have been highly inhomogeneous. The current paradigm attempts to answer this problem by postulating the inflation mechanism. However, inflation in order to start requires a homogeneous patch of at least the horizon size. This paper examines if dynamical processes of the early universe could lead to homogenization. In the past similar studies seem to imply that the set of initial conditions that leads to homogenization is of measure zero. This essay proves the contrary: a set of initial conditions for spontaneous homogenization of cosmological models can form a set of nonzero measure.

Role of a scalar field in the radiation dominated epoch of the development of the universe

Abstract: The recently discovered accelerated expansion of the universe is of current interest in theoretical research on the evolution of the universe. The cause of this behavior is presumably the presence of dark energy, which has been estimated to form up to 70% of the universe and generates a “repulsive force.” In this paper a cosmological model is constructed which takes the dark energy into account in a Jordan-Brans-Dicke tensor-scalar model with a dominant, nonminimally coupled scalar field in the presence of a cosmological scalar. The radiation dominant epoch is discussed.