Particle horizon

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

Material content of the Universe: introductory survey

Abstract: Matter in the Universe can be detected either by the radiation it emits or by its gravitational influence. There is a strong suggestion that the Universe contains substantial hidden matter, mass without corresponding light. There are also arguments from elementary particle physics that the Universe should have closure density, which would also imply hidden mass. Observations of the chemical composition of the Universe interpreted in terms of the hot Big Bang cosmological theory suggest that this hidden matter cannot all be of baryonic form but must consist of weakly interacting elementary particles. A combination of observations and theoretical ideas about the origin of large-scale structure may demand that these particles are of a type which is not yet definitely known to exist.

Slipher's redshifts as support for de Sitter's model and the discovery of the dynamic universe

Abstract: Of the first two relativistiv world models, only the one by de Sitter predicted redshifted spectra from far away astronomical objects. Slipher's redshifts therefore seemed to arbitrate against Einstein's model which made no such predictions. Both models were trying to describe a static universe. However, Lemaitre found that de Sitter's construct resulted in a spatially inhomogeneous universe. He then opted for a model that correspondes to Einstein's closed, curved universe but allowed the radius of curvature to change with time. Slipher's redshifts suggested to him that the universe is dynamic and expanding. We also discuss the respective merits of Friedman and Lemaitre in revealing the dynamic nature of the universe.

Did the Universe exist prior to the accelerating stage

Abstract: Dark energy recently began to dominate in the Universe, making its expansion accelerating. If dark energy is assumed to originate from a quintessence field, we have obtained consistent cosmological solutions to the Friedmann equations for an accelerating universe which can be interpreted as compactified Lorentzian wormholes; we shown that then, unlike asymptotically de Sitter spaces, there should be no event horizons placed at finite distances in the future, in the spacetimes described by these FRW solutions, even for constant quintessence equations of state predicting acceleration. It is argued that it is the existence of signals travelling backward in time that prevents event horizons to occur at finite distances in the future in these space-times. We have also solved the Friedmann equations for different regimes that preceded our present accelerating era and are predicted by quintessence tracking models. As an alternative proposal to the tracked description, we further suggest a new cosmological scenario where the entire evolution of the Universe prior to the present accelerating expansion occurred in a Euclidean regime with imaginary time, and the primordial inflation is viewed as an artifact originating from Lorentzian causality underlying all current physical instruments and hence the results they provide and their interpretation. By recourse to the noted analogy between this cosmological scenario and the epistemological aspects of Plato’s cave myth of ancient Greek philosophy that concern geometric forms, we call the resulting universe model a Platonic universe.