Particle Horizon Research Articles

Recent CMB observations enable to find the total gravitational energy of a mass.

The astronomical observations indicate that the universe expands with acceleration and it has a finite particle horizon. The recent CMB observations confirm the universe is homogeneous, isotropic and asymptotically flat. The total gravitational energy of a body having mass m is the gravitational potential energy originating from the gravitational interaction of the body with all masses of the observable universe, i.e. within the particle horizon. The flat geometry of the universe enables to determine the total gravitational energy of the mass m within the framework of the Newtonian gravity in Euclidean space. By this approach, it has been found the modulus of the total gravitational energy of a body is close to its rest energy E = mc 2 , which is a remarkable result. Besides, the smoothed gravitational potential in an arbitrary point of the observable universe appears close to −c 2 , where

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

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 .

Emergent horizons in the laboratory

The concept of a horizon known from general relativity describes the loss of causal connection and can be applied to non-gravitational scenarios such as out-of-equilibrium condensed-matter systems in the laboratory. This analogy facilitates the identification and theoretical study (e.g., regarding the trans-Planckian problem) and possibly the experimental verification of ‘exotic’ effects known from gravity and cosmology, such as Hawking radiation. Furthermore, it yields a unified description and better understanding of non-equilibrium phenomena in condensed-matter systems and their universal features. By means of several examples including general fluid flows, expanding Bose–Einstein condensates and dynamical quantum phase transitions, the concepts of event, particle and apparent horizons will be discussed together with the resulting quantum effects.

Dark energy due to effective quantum field theory

In the cosmological context an effective quantum field theory describing the behavior of visible matter in the Universe is characterized with its inherent UV cutoff and also with an IR scale that is set by the cosmological (particle) horizon. This UV–IR relation naturally defines a space–time grid over a horizon scale. Using the approach for determining of dark energy through the space–time uncertainty relation versus such a space–time grid, we estimate the energy density and pressure of a dark energy defined by this UV–IR relation. Such a dark energy shows up to decay linearly with time and exhibits a negative pressure only recently.

The Inimitable Field of Cosmology

In the News Focus article “A singular conundrum: How odd is our universe?” (28 September 2007, p. [1848][1]), A. Cho perpetuated misunderstanding of science with the statement, in part from James Gunn, that “'Cosmology may look like a science, but it isn't a science' because it's impossible to do repeatable experiments.” In the truly natural sciences (such as geology, oceanography, atmospheric science, and ecology), rigorous observation and interpretation are commonly used, rather than “repeatable experiments” a la Karl Popper—except in those few cases where a small-scale experiment is meaningful ([1][2]). It would be better to say that cosmology is science—it just isn't Popperian physics. 1. 1.[↵][3]1. C. M. Condit, 2. L. B. Railsback , The Transilience Project [www.gly.uga.edu/railsback/Transilience/Transilience.html][4]). # Response {#article-title-2} With all due respect, I think that L. B. Railsback misses the point that I was attempting to make. The pursuit of understanding the cosmos is certainly a scientific pursuit and makes use of many of the most powerful tools of science. Unfortunately, there is only one observable universe, and while it is quite possible in principle, and probably in practice, to formulate theories that describe its observed behavior perfectly on the largest scales, those theories could well be unverifiable by any doable experiment. In geophysics and astrophysics, the experimenter is nature, not the scientist, but repeated experiments can be done and the results can be observed. This is not so in cosmology for phenomena on the largest scales. Further confusion stems from our belief that the structure we are observing is stochastic on scales up to and beyond the current particle horizon. As discussed in the News Focus article, we may be unlucky enough to live in a volume in which some large-scale quantity assumes a very unlikely value within the framework of some otherwise seemingly successful theory. It then becomes a very subjective matter of whether this observation does or does not rule out the theory in question. Whatever one's view on the Popperian definition, verification by whatever technique is a cornerstone of science; I am merely saying that this can be impossible for crucial and interesting aspects of cosmological inquiry. [1]: /lookup/doi/10.1126/science.317.5846.1848 [2]: #ref-1 [3]: #xref-ref-1-1 View reference 1. in text [4]: http://www.gly.uga.edu/railsback/Transilience/Transilience.html

Dynamics of holographic vacuum energy in the DGP model

We consider the evolution of the vacuum energy in the Dvali-Gabadadze-Porrati (DGP) model according to the holographic principle under the assumption that the relation linking the IR and UV cutoffs still holds in this scenario. The model is studied when the IR cutoff is chosen to be the Hubble scale H(-1), the particle horizon R(ph), and the future event horizon R(eh), respectively. The two branches of the DGP model are also taken into account. Through numerical analysis, we find that in the cases of H(-1) in the (+) branch and R(eh) in both branches, the vacuum energy can play the role of dark energy. Moreover, when considering the combination of the vacuum energy and the 5D gravity effect in both branches, the equation of state of the effective dark energy may cross -1, which may lead to the big rip singularity. Besides, we constrain the model with the Type Ia supernovae and baryon oscillation data and find that our model is consistent with current data within 1 sigma, and that the observations prefer either a pure holographic dark energy or a pure DGP model.

Saturation of the Holographic Principle for Spatially Closed Cosmological Models

Under the assumption on the fundamental character of the Holographic Principle as a primary principle guiding the behavior of our universe the saturation of the holographic limit is reasonable. On the other hand the Fischler-Susskind holographic prescription seems to be incompatible with closed cosmological models due to the apparently unavoidable recontraction of the particle horizon area. However we will show that the saturation of the Fischler-Susskind holographic prescription over a closed (although almost flat) cosmological model enforces a cosmological evolution very similar to the observed universe.

Cosmology with galaxy correlations

In this review, I outline the use of galaxy correlations to constrain cosmological parameters. As with the cosmic microwave background (CMB), the density of dark and baryonic matter imprints important scales on the fluctuations of matter and thus the clustering of galaxies, e.g., the particle horizon at matter-radiation equality and the sound horizon at recombination. Precision measurements of these scales from the baryon acoustic oscillations (BAO) and the large scale shape of the power spectrum of galaxy clustering provide constraints on Ω m h 2. Recent measurements from the Sloan Digital Sky Survey (SDSS) and 2dF Galaxy Redshift Survey (2dFGRS) strongly suggest that Ω m < 0.3. This forms the basic evidence for a flat Universe dominated by a Cosmological Constant (Λ) today (when combined with results from the CMB and supernova surveys). Further evidence for this cosmological model is provided by the late-time Integrated Sachs–Wolfe (ISW) effect, which has now been detected using a variety of tracers of the large scale structure in the Universe out to redshifts of z > 1. The ISW effect also provides an opportunity to discriminate between Λ, dynamical dark energy models and the modification of gravity on large scales.

Cosmology 101 Revisited.

Arguments are presented to show that the current standard model of the cosmos always violates the energy conservation law, even when it shouldn’t for asymptotically flat space-time in a closed system, and that such a violation can be linked analytically to the use of a radially focused Robertson–Walker (RW) based distance metric. Results are also presented to show how certain standard-model assumptions strongly affect particle horizon attributes and how the analytical use of a θ -axis-focused RW distance metric can serve as a vehicle to demonstrate the impact of matter-based gravitation on photon trajectory attributes that can be associated with energy conservation in flat space-time.

Fischler–Susskind holographic cosmology revisited

When Fischler and Susskind proposed a holographic prescription based on the particle horizon, they found that spatially closed cosmological models do not verify it due to the apparently unavoidable recontraction of the particle horizon area. In this paper, after a short review of their original work, we expose graphically and analytically that spatially closed cosmological models can avoid this problem if they expand fast enough. It has also been shown that the holographic principle is saturated for a codimension one-brane dominated universe. The Fischler–Susskind prescription is used to obtain the maximum number of degrees of freedom per Planck volume at the Planck era compatible with the holographic principle.

Modified teleparallel gravity: Inflation without an inflaton

The Born-Infeld strategy to smooth theories having divergent solutions is applied to the teleparallel equivalent of general relativity. Differing from other theories of modified gravity, modified teleparallelism leads to second order equations, since the teleparallel Lagrangian only contains first derivatives of the vierbein. We show that the Born-Infeld-modified teleparallelism solves the particle horizon problem in a spatially flat Friedmann-Robertson-Walker (FRW) universe by providing an initial exponential expansion without resorting to an inflaton field.

An alternative approach to holographic dark energy

Here we consider a scenario in which dark energy is associated with the apparent area of asurface in the early universe. In order to resemble the cosmological constant at late times,this hypothetical reference scale should maintain an approximately constant physical sizeduring an asymptotically de Sitter expansion. This is found to arise when the particlehorizon—anticipated to be significantly greater than the Hubble length—is approaching theantipode of a closed universe. Depending on the constant of proportionality, either theensuing inflationary period prevents the particle horizon from vanishing, or it may lead to asequence of ‘big rips’.

Is Space Really Expanding? A Counterexample

In all Friedman models, the cosmological redshift is widely interpreted as a consequence of the general-relativistic phenomenon of expansion of space. Other commonly believed consequences of this phenomenon are superluminal recession velocities of distant galaxies, and the distance to the particle horizon greater than ct (where t is the age of the Universe), in apparent conflict with special relativity. Here, we study a particular Friedman model: empty universe. This model exhibits both cosmological redshift, superluminal velocities and infinite distance to the horizon. However, we show that the cosmological redshift is there simply a relativistic Doppler shift. Moreover, apparently superluminal velocities and ‘acausal’ distance to the horizon are in fact a direct consequence of special-relativistic phenomenon of time dilation, as well as of the adopted definition of distance in cosmology. There is no conflict with special relativity, whatsoever. In

Holographic Dark Energy in Induced Gravity

Many astrophysics data show that our universe has a critical energy density, and 73% of it is dark energy, which drives the accelerating expansion of the universe. We consider the holographic dark energy in induced gravity by taking the Hubble scale, particle horizon and event horizon as the infrared cutoff. We find that only the event horizon can give accelerating expansion of our universe.

HOW MANY UNIVERSES DO THERE NEED TO BE?

In the simplest cosmological models consistent with General Relativity, the total volume of the Universe is either finite or infinite, depending on whether or not the spatial curvature is positive. Current data suggest that the curvature is very close to flat, implying that one can place a lower limit on the total volume. In a Universe of finite age, the "particle horizon" defines the patch of the Universe which is observable to us. Based on today's best-fit cosmological parameters it is possible to constrain the number of observable Universe sized patches, NU. Specifically, using the new Wilkinson Microwave Anisotropy Probe (WMAP) data, we can say that there are at least 21 patches out there the same volume as ours, at 95% confidence. Moreover, even if the precision of our cosmological measurements continues to increase, density perturbations at the particle horizon size limit us to never knowing that there are more than about 105 patches out there.

Generalized uncertainty principle, modified dispersion relations and the early universe thermodynamics

In this paper, we study the effects of Generalized Uncertainty Principle (GUP) and Modified Dispersion Relations (MDRs) on the thermodynamics of ultra-relativistic particles in early universe. We show that limitations imposed by GUP and particle horizon on the measurement processes, lead to certain modifications of early universe thermodynamics.

Thin Domain Walls in Lyra Geometry

This paper studies thin domain walls within the frame work of Lyra Geometry. We have considered two models. First one is the thin domain wall with negligible pressures perpendicular and transverse direction to the wall and secondly, we take a particular type of thin domain wall where the pressure in the perpendicular direction is negligible but transverse pressures are existed. It is shown that the thin domain walls have no particle horizon and the gravitational force due to them is attractive.

Unifying phantom inflation with late-time acceleration: scalar phantom–non-phantom transition model and generalized holographic dark energy

The unifying approach to early-time and late-time universe based on phantom cosmology is proposed. We consider gravity-scalar system which contains usual potential and scalar coupling function in front of kinetic term. As a result, the possibility of phantom-non-phantom transition appears in such a way that universe could have effectively phantom equation of state at early time as well as at late time. In fact, the oscillating universe may have several phantom and non-phantom phases. As a second model we suggest generalized holographic dark energy where infrared cutoff is identified with combination of FRW parameters: Hubble constant, particle and future horizons, cosmological constant and universe life-time (if finite). Depending on the specific choice of the model the number of interesting effects occur: the possibility to solve the coincidence problem, crossing of phantom divide and unification of early-time inflationary and late-time accelerating phantom universe. The bound for holographic entropy which decreases in phantom era is also discussed.

Role of the Brans–Dicke scalar in the holographic description of dark energy

We study cosmological application of the holographic energy density in the Brans–Dicke theory. Considering the holographic energy density as a dynamical cosmological constant, it is more natural to study it in the Brans–Dicke theory than in general relativity. Solving the Friedmann and Brans–Dicke field equations numerically, we clarify the role of Brans–Dicke field during evolution of the universe. When the Hubble horizon is taken as the IR cutoff, the equation of state (wΛ) for the holographic energy density is determined to be 53 when the Brans–Dicke parameter ω goes infinity. This means that the Brans–Dicke field plays a crucial role in determining the equation of state. For the particle horizon IR cutoff, the Brans–Dicke scalar mediates a transition from wΛ=−1/3 (past) to wΛ=1/3 (future). If a dust matter is present, it determines future equation of state. In the case of future event horizon cutoff, the role of the Brans–Dicke scalar and dust matter are turned out to be trivial, whereas the holographic energy density plays an important role as a dark energy candidate with wΛ=−1.

Asymptotic Silence of Generic Cosmological Singularities

In this Letter we investigate the nature of generic cosmological singularities using the framework developed by Uggla et al. We study the past asymptotic dynamics of general vacuum G2 cosmologies, which are expected to capture the singular behavior of generic cosmologies with no symmetries at all. Our results indicate that asymptotic silence holds, i.e., particle horizons along all time lines shrink to zero for generic solutions. Moreover, we provide evidence that spatial derivatives become dynamically insignificant along generic time lines, and that the evolution into the past along such time lines is governed by an asymptotic dynamical system which is associated with an invariant set-the silent boundary. We identify an attracting subset on the silent boundary that organizes the oscillatory dynamics of generic time lines in the singular regime. Finally, we discuss the dynamics associated with recurring spike formation.