Particle horizon

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

Cosmological constant caused by observer-induced boundary condition

Abstract: The evolution of the wave function in quantum mechanics is deterministic like that of classical waves. Only when we bring in observers the fundamentally different quantum reality emerges. Similarly the introduction of observers changes the nature of spacetime by causing a split between past and future, concepts that are not well defined in the observer-free world. The induced temporal boundary leads to a resonance condition for the oscillatory vacuum solutions of the metric in Euclidean time. It corresponds to an exponential de Sitter evolution in real time, which can be represented by a cosmological constant $\Lambda =2\pi^2/r_u^2$, where $r_u$ is the radius of the particle horizon at the epoch when the observer exists. For the present epoch we get a value of $\Lambda$ that agrees with the observed value within $2\sigma$ of the observational errors. This explanation resolves the cosmic coincidence problem. Our epoch in cosmic history does not herald the onset of an inflationary phase driven by some dark energy. We show that the observed accelerated expansion that is deduced from the redshifts is an "edge effect" due to the observer-induced boundary and not representative of the intrinsic evolution. The new theory satisfies the BBN (Big Bang nucleosynthesis) and CMB (cosmic microwave background) observational constraints equally well as the concordance model of standard cosmology. There is no link between the dark energy and dark matter problems. Previous conclusions that dark matter is mainly non-baryonic are not affected.

Dark Energy in Light of the Cosmic Horizon

Abstract: Based on dramatic observations of the CMB with WMAP and of Type Ia supernovae with the Hubble Space Telescope and ground-based facilities, it is now generally believed that the Universe's expansion is accelerating. Within the context of standard cosmology, the Universe must therefore contain a third `dark' component of energy, beyond matter and radiation. However, the current data are still deemed insufficient to distinguish between an evolving dark energy component and the simplest model of a time-independent cosmological constant. In this paper, we examine the role played by our cosmic horizon R0 in our interrogation of the data, and reach the rather firm conclusion that the existence of a cosmological constant is untenable. The observations are telling us that R0=c t0, where t0 is the perceived current age of the Universe, yet a cosmological constant would drive R0 towards ct (where t is the cosmic time) only once, and that would have to occur right now. In contrast, scaling solutions simultaneously eliminate several conundrums in the standard model, including the `coincidence' and `flatness' problems, and account very well for the fact that R0=c t0. We show here that for such dynamical dark energy models, either R0=ct for all time (thus eliminating the apparent coincidence altogether), or that what we believe to be the current age of the universe is actually the horizon time th=R0/c, which is always shorter than t0. Our best fit to the Type Ia supernova data indicates that t0 would then have to be ~16.9 billion years. Though surprising at first, an older universe such as this would actually eliminate several other long-standing problems in cosmology, including the (too) early appearance of supermassive black holes (at a redshift > 6) and the glaring deficit of dwarf halos in the local group.

C-field cosmological model for barotropic fluid distribution with bulk viscosity and decaying vacuum energy (Λ) in FRW space–time

Abstract: A solution of Einstein’s field equations that admits barotropic fluid distribution and a negative-energy massless scalar creation field as a source in the presence of bulk viscosity and time-dependent vacuum energy density (Λ) is investigated. It is shown that a cosmological model based on this solution satisfies observational tests and is thus a viable alternative to the standard Big Bang model. The present model is free from real singularity and particle horizon. The creation field increases with time, which matches the result as obtained by Hoyle and Narlikar (Proc. Roy. Soc. A, 282, 178 (1964)). The vacuum energy density, Λ ∼ t–2, matches the result as obtained by Bertolami (Nuovocim. B, 93, 36 (1986)). The spatial volume increases exponentially with time. Thus the model has an inflationary scenario. The deceleration parameter q < 0 indicating that the model represents accelerating expansion of the universe. The presence of the creation field prevents matter density from vanishing and it remains const...

Quantum evolution of the Universe in the constrained quasi-Heisenberg picture: from quanta to classics?

Abstract: The quasi-Heisenberg picture of minisuperspace model is considered The The quasi-Heisenberg picture of minisuperspace model is considered The suggested scheme consists in quantizing of the equation of motion and interprets all observables including the Universe scale factor as the time-dependent (quasi-Heisenbeg) operators acting in the space of solutions of the Wheeler--DeWitt equation The Klein-Gordon normalization of the wave function and corresponding to it quantization rules for the equation of motion allow a time-evolution of the mean values of operators even under constraint H=0 on the physical states of Universe Besides, the constraint H=0 appears as the relation connecting initial values of the quasi-Heisenbeg operators at $t=0$ A stage of the inflation is considered numerically in the framework of the Wigner--Weyl phase-space formalism For an inflationary model of the ``chaotic inflation'' type it is found that a dispersion of the Universe scale factor grows during inflation, and thus, does not vanish at the inflation end It was found also, that the ``by hand'' introduced dependence of the cosmological constant from the scale factor in the model with a massless scalar field leads to the decrease of dispersion of the Universe scale factor The measurement and interpretation problems arising in the framework of our approach are considered, as well

Determination of total mechanical energy of the universe within the framework of Newtonian mechanics

Abstract: The recent astronomical observations indicate that the expanding universe having a finite particle horizon is homogeneous, isotropic and asymptotically flat. The Euclidean geometry of the universe enables to determine the total kinetic and gravitational energies of the universe within the framework of the Newtonian mechanics. It has been shown that almost the entire kinetic energy of the universe ensues from the cosmological expansion. Both, the total kinetic and gravitational energies of the universe have been determined in relation to an observer at arbitrary location. It is amazing that the modulus of the total gravitational energy differs from the total kinetic energy with a multiplier close to a unit. Thus, the total mechanical energy of the universe has been found close to zero. Both, the total kinetic energy and the modulus of total gravitational energy of the universe are estimated to 3/10 of its total rest energy Mc 2 .