Compact Note On Supposed Cosmic Inflation

Astronomy & Astrophysics, 2013

Context. The horizon problem in the standard model of cosmology (ΛDCM) arises from the observed uniformity of the cosmic microwave background radiation, which has the same temperature everywhere (except for tiny, stochastic fluctuations), even in regions on opposite sides of the sky, which appear to lie outside of each other's causal horizon. Since no physical process propagating at or below lightspeed could have brought them into thermal equilibrium, it appears that the universe in its infancy required highly improbable initial conditions. Aims. In this paper, we demonstrate that the horizon problem only emerges for a subset of FRW cosmologies, such as ΛCDM, that include an early phase of rapid deceleration. Methods. The origin of the problem is examined by considering photon propagation through a Friedmann-Robertson-Walker (FRW) spacetime at a more fundamental level than has been attempted before. Results. We show that the horizon problem is nonexistent for the recently introduced R h = ct universe, obviating the principal motivation for the inclusion of inflation. We demonstrate through direct calculation that, in this cosmology, even opposite sides of the cosmos have remained causally connected to us-and to each other-from the very first moments in the universe's expansion. Therefore, within the context of the R h = ct universe, the hypothesized inflationary epoch from t = 10 −35 seconds to 10 −32 seconds was not needed to fix this particular "problem," though it may still provide benefits to cosmology for other reasons.

Monthly Notices of the Royal Astronomical Society, 2012

The Hubble radius is a particular manifestation of the Universe's gravitational horizon, R h (t 0 ) ≡ c/H 0 , the distance beyond which physical processes remain unobservable to us at the present epoch. Based on recent observations of the cosmic microwave background (CMB) with Wilkinson Microwave Anisotropy Probe, and ground-based and Hubble Space Telescope searches for Type Ia supernovae, we now know that R h (t 0 ) ∼13.5 Glyr. This coincides with the maximum distance (ct 0 ≈ 13.7 Glyr) light could have travelled since the big bang. However, the physical meaning of R h is still not universally understood or accepted, though the minimalist view holds that it is merely the proper distance at which the rate of cosmic recession reaches the speed of light c. Even so, it is sometimes argued that we can see light from sources beyond R h , the claim being that R h lies at a redshift of only ∼2, whereas the CMB was produced at a much greater redshift (∼1100). In this paper, we build on recent developments with the gravitational radius by actually calculating null geodesics for a broad range of Friedmann-Robertson-Walker cosmologies, to show -at least in the specific cases we consider here, including cold dark matter ( CDM) -that no photon trajectories reaching us today could have ever crossed R h (t 0 ). We therefore confirm that the current Hubble radius, contrary to a commonly held misconception, is indeed the limit to our observability. We find that the size of the visible universe in CDM, measured as a proper distance, is approximately 0.5ct 0 .

International Journal of Current Research and Academic Review, 2017

Article Info The Standard Big Bang Cosmology gives the most accepted concept about the beginning and evolution of the Universe. However, it has problems: the flatness problem, the horizon problem and the monopole problem. The predictions of the Standard Big Bang Cosmology do not match the observations of modern cosmologists. Nonetheless, the admirers of the Standard Big Bang Cosmology continued to find out ways for solving those problems and such attempts lead to our knowledge of Inflationary Cosmology. The theory of inflation, which was first proposed by Alan Guth in 1981, soon became a "need" of modern cosmology and various modified models of inflationary Universe were proposed. In this paper, the author gives a brief insight of the Standard Big Bang Cosmology, introduces inflationary cosmology with its brief background, reviews some concepts associated with cosmic inflation, explains how inflation can be classified into various types, describes few of the popular types in brief and explains how the cosmological problems are solved by cosmic inflation. Moreover, few insightful examples have been given to easily explain the fundamental concepts so that even a junior researcher can get thorough idea about the field by escaping the equations and simply going through the text selectively.

2023

This dissertation begins by exploring the distance ladder in cosmology, which is used to measure astronomical distances and is crucial to our understanding of the universe’s size and scale. The dissertation then provides an overview of the General Theory of Relativity and its application to the Friedmann-Robertson-Walker (FRW) Universe, which is a model of the universe that assumes it is homogeneous and isotropic on large scales. Then it explores the dynamics and properties of FRW Universe. Apart from having unmatched successes, Big Bang theory still has some problems, including the horizon problem, flatness problem, and monopole problem. To address these issues, a new theory was proposed in the 1980s known as Cosmic Inflation. The dissertation explains how the Slow Roll Model and Power Law Potential can be used to describe the inflaton field’s behavior during the inflationary period. Then it reviews some other inflation models and reheating. We also study the Cosmic Microwave Background Radiation(CMBR), which is the residual radiation left over from the Big Bang as a solution to these problems. The CMBR provides a window into the early universe, and its properties can be used to study the universe’s evolution. Finally, the paper concludes by discussing Precision Cosmology, which involves using data from Supernova Ia to estimate cosmological parameters. The paper also discusses the results from Wilkinson Microwave Anisotropy Probe(WMAP) and Planck data, which provide strong evidence for Cosmic Inflation. This data has also been successfully used to constrain the parameters of the inflaton field. Through this comprehensive analysis, the paper provides a detailed and informative overview of Cosmic Inflation and its significance in modern cosmology.

In this study, we use the Friedman-Robertson-Walker (FRW) model with κ = +1 for cyclic universe for understanding the physics of cosmic inflation. According to this model, kinetic energy of the universe is converted into gravitational energy during deceleration (compression) cycle. This builds up a dense assembly of photons close to the singularity of Planck dimensions at temperature T ~ < T PL. Black body radiation approximation is used to analyze the distribution of the photons in the phase space using quantum statistical mechanics. It is shown that the available states in the phase space are completely filled up when the temperature reaches T E. When the temperature increases above T E , the assembly of superheated photons transforms to a non-equilibrium state. We show that an adiabatic transition from the non-equilibrium state to equilibrium state at T E is accompanied by the inflation of space-time and the big bang. The measurements of the red shifts of radiation from very distant galaxies and the measurement of anisotropy in Cosmic Microwave Background using Wilkinson and Planck observatories have confirmed that dark matter and dark energy (or a positive cosmological constant  make contribution to the expansion of the universe. We discuss here the mechanism which builds up large amount of energy E ps 1 in the phase space created during the cosmic inflation. We propose that this energy is the source of the cosmological constant . Other mechanisms which transfer some of the energy released during the inflation to the observable universe are also discussed. The contribution from these sources to  is comparatively small.

Studying the universe, understanding its origin and evolution has always been of great interest to humanity. In this context, cosmology proposes it, seeking to answer questions related to its structure, composition, and dynamics. Initially, there were various proposed models, but the one that has achieved considerable success when compared with different cosmological observations was the Hot Big Bang model. This implies a universe in expansion, homogeneous and isotropic on a large scale, that is, there are no preferred points or directions in the universe (WEINBERG, 2008). However, despite its great success, it has some problems, among them the horizon and flatness problems can be highlighted. A widely accepted proposal to solve them is that the universe, at its initial moment, underwent a phase of exponential growth. Such a proposal constitutes what is known as inflationary models, which, in addition to solving the problems present in the Hot Big Bang model, provides a good explanation for the formation of the anisotropies of the universe as a result of the expansion of quantum fluctuations in the scalar field generating the inflationary period called inflaton.

Astrophysics and Space Science Proceedings, 2008

We present a brief review of Cosmological Inflation from the personal perspective of the author who almost 30 years ago proposed a way of resolving the problem of Cosmological Horizon by employing certain notions and developments from the field of High Energy Physics. Along with a brief introduction of the Horizon and Flatness problems of standard cosmology, this lecture concentrates on personal reminiscing of the notions and ideas that prevailed and influenced the author's thinking at the time. The lecture then touches upon some more recent developments related to the subject and concludes with some personal views concerning the direction that the cosmology field has taken in the past couple of decades and certain speculations some notions that may indicate future directions of research.

The Hubble radius is a particular manifestation of the Universe&#39;s gravitational horizon, R_h(t_0)=c/H_0, the distance beyond which physical processes remain unobservable to us at the present epoch. Based on recent observations of the cosmic microwave background (CMB) with WMAP, and ground-based and HST searches for Type Ia supernovae, we now know that R_h(t_0)~13.5 Glyr. This coincides with the maximum distance (ct_0~13.7 Glyr) light could have traveled since the big bang. However, the physical meaning of R_h is still not universally understood or accepted, though the minimalist view holds that it is merely the proper distance at which the rate of cosmic recession reaches the speed of light c. Even so, it is sometimes argued that we can see light from sources beyond R_h, the claim being that R_h lies at a redshift of only ~2, whereas the CMB was produced at a much greater redshift (~1100). In this paper, we build on recent developments with the gravitational radius by actually c...

Physical Review D, 1981

The standard model of hot big bang cosmology requires initial conditions which are problematic in two ways: (1) the early universe is assumed to be highly homogeneous, in spite of the fact that separated regions were causally disconnected (horizon problem); and (2) the initial value of the Hubble constant must be fine tuned to extraordinary accuracy to produce a universe as flat (i.e., near critical mass density) as'the one we see today (flatness problem). These problems would disappear if, in its early history, the universe supercooled to temperatures 28 or more orders of magnitude below the critical temperature for some phase transition. A huge expansion factor would then result from a period of exponential growth, and the entropy of the universe would be multiplied by a huge factor when the latent heat is released. Such a scenario is completely natural in the context of grand unified models of elementary particle interactions. In such models, the supercooling is also relevant to the problem of monopole suppression. Unfortunately, the scenario seems to lead to some unacceptable consequences, so modifications must be sought.

Journal of Cosmology and Astroparticle Physics, 2014

In this article we discuss the role of current and future CMB measurements to pin down the model of inflation responsible for the generation of primordial curvature perturbations. By considering a parameterization of the effective field theory of inflation with a modified dispersion relation arising from heavy fields, we derive the dependence of cosmological observables on the scale of heavy physics Λ UV . Specifically, we show how the f NL non-linearity parameters are related to the phase velocity of curvature perturbations at horizon exit, which is parameterized by Λ UV . Bicep2 and Planck findings are shown to be consistent with a value Λ UV ∼ Λ GUT . However, we find a degeneracy in the parameter space of inflationary models that can only be resolved with a detailed knowledge of the shape of the non-Gaussian bispectrum.