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Symmetry
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New Advances of Cosmology and Astrophysics
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New Advances of Cosmology and Astrophysics

A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (19 November 2021) | Viewed by 18513

Special Issue Editor

Prof. Dr. Lawrence Horwitz

E-Mail Website1 Website2
Guest Editor
1. Department of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
2. Department of Physics, Bar Ilan University, Ramat Gan 52900, Israel
3. Department of Physics, Ariel University, Ariel 40700, Israel
Interests: relativistic quantum mechanics and quantum field theory; theory of classical and quantum unstable systems and chaos; quantum theory on hypercomplex Hilbert modules; complex projective spaces in quantum dynamics; relativistic statistical mechanics and thermodynamics; high-energy nuclear structure and particle physics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In recent years, the development of powerful telescopes, along with advanced computer facilities and sophisticated programs, have revealed that the structure of galaxies does not agree with simple static Newtonian mechanics. The assumption of the existence of some kind of dark matter is able to account for observed rotation curves, but so far, there are no viable candidates for this matter, and there is some evidence that estimates of the Hubble constant may not be consistent. There has been a number of proposed alternative theories; the situation is rapidly developing, and it will be important at this stage to express these new ideas and results in the Special Issue of Symmetry that is being planned.

Prof. Lawrence Horwitz
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • galaxy structure
  • rotation curves
  • modified Newtonian dynamics
  • dark matter
  • lensing
  • dark energy

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Published Papers (6 papers)

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Research

5 pages, 215 KiB  
Article
Entropy Bounds: New Insights
by Lawrence Paul Horwitz, Vishnu S. Namboothiri, Gautham Varma K, Asher Yahalom, Yosef Strauss and Jacob Levitan
Symmetry 2022, 14(1), 126; https://doi.org/10.3390/sym14010126 - 10 Jan 2022
Viewed by 2891
Abstract
In this paper we review the fundamental concepts of entropy bounds put forward by Bousso and its relation to the holographic principle. We relate covariant entropy with logarithmic distance of separation of nearby geodesics. We also give sufficient arguments to show that the [...] Read more.
In this paper we review the fundamental concepts of entropy bounds put forward by Bousso and its relation to the holographic principle. We relate covariant entropy with logarithmic distance of separation of nearby geodesics. We also give sufficient arguments to show that the origin of entropy bounds is not indeed thermodynamic, but statistical. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
23 pages, 445 KiB  
Article
Lensing Effects in Retarded Gravity
by Asher Yahalom
Symmetry 2021, 13(6), 1062; https://doi.org/10.3390/sym13061062 - 12 Jun 2021
Cited by 11 | Viewed by 2932
Abstract
Galaxies are gigantic physical systems having a typical size of many tens of thousands of light years. Thus, any change at the center of the galaxy will affect the rim only tens of millennia later. Those retardation effects seem to be ignored in [...] Read more.
Galaxies are gigantic physical systems having a typical size of many tens of thousands of light years. Thus, any change at the center of the galaxy will affect the rim only tens of millennia later. Those retardation effects seem to be ignored in present day modelling used to calculate rotational velocities of matter in the outskirts of the galaxy and the surrounding gas. The significant discrepancies between the velocities predicted by Newtonian theory and observed velocities are usually handled by either assuming an unobservable type of matter denoted “dark matter” or by modifying the laws of gravity (MOND as an example). Here, we will show that considering general relativistic effects without neglecting retardation can explain the apparent excess matter leading to gravitational lensing in both galaxies and galaxy clusters. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
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18 pages, 398 KiB  
Article
An Anisotropic Model for the Universe
by Morgan Le Delliou, Maksym Deliyergiyev and Antonino del Popolo
Symmetry 2020, 12(10), 1741; https://doi.org/10.3390/sym12101741 - 21 Oct 2020
Cited by 8 | Viewed by 2462
Abstract
Motivated by the back-reaction debate, and some unexplained characteristics of the CMB, we investigate the possibility of some anisotropy in the universe observed around us. To this aim, we build up a novel prediction for the Hubble law for the late universe from [...] Read more.
Motivated by the back-reaction debate, and some unexplained characteristics of the CMB, we investigate the possibility of some anisotropy in the universe observed around us. To this aim, we build up a novel prediction for the Hubble law for the late universe from a Bianchi type I model, taken as proof of concept, transcribing the departure of such model from a ΛCDM model. We dicussed the redshift measurement in this universe, and finally formalized the Hubble diagram. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
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29 pages, 376 KiB  
Article
A 4+1 Formalism for the Evolving Stueckelberg-Horwitz-Piron Metric
by Martin Land
Symmetry 2020, 12(10), 1721; https://doi.org/10.3390/sym12101721 - 19 Oct 2020
Cited by 7 | Viewed by 1884
Abstract
We propose a field theory for the local metric in Stueckelberg–Horwitz–Piron (SHP) general relativity, a framework in which the evolution of classical four-dimensional (4D) worldlines xμτ (μ=0,1,2,3) is parameterized by an [...] Read more.
We propose a field theory for the local metric in Stueckelberg–Horwitz–Piron (SHP) general relativity, a framework in which the evolution of classical four-dimensional (4D) worldlines xμτ (μ=0,1,2,3) is parameterized by an external time τ. Combining insights from SHP electrodynamics and the ADM formalism in general relativity, we generalize the notion of a 4D spacetime M to a formal manifold M5=M×R, representing an admixture of geometry (the diffeomorphism invariance of M) and dynamics (the system evolution of Mτ with the monotonic advance of τ∈R). Strategically breaking the formal 5D symmetry of a metric gαβ(x,τ) (α,β=0,1,2,3,5) posed on M5, we obtain ten unconstrained Einstein equations for the τ-evolution of the 4D metric γμν(x,τ) and five constraints that are to be satisfied by the initial conditions. The resulting theory differs from five-dimensional (5D) gravitation, much as SHP U(1) gauge theory differs from 5D electrodynamics. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
24 pages, 1271 KiB  
Article
Lorentz Symmetry Group, Retardation, Intergalactic Mass Depletion and Mechanisms Leading to Galactic Rotation Curves
by Asher Yahalom
Symmetry 2020, 12(10), 1693; https://doi.org/10.3390/sym12101693 - 15 Oct 2020
Cited by 18 | Viewed by 3153
Abstract
The general theory of relativity (GR) is symmetric under smooth coordinate transformations, also known as diffeomorphisms. The general coordinate transformation group has a linear subgroup denoted as the Lorentz group of symmetry, which is also maintained in the weak field approximation to GR. [...] Read more.
The general theory of relativity (GR) is symmetric under smooth coordinate transformations, also known as diffeomorphisms. The general coordinate transformation group has a linear subgroup denoted as the Lorentz group of symmetry, which is also maintained in the weak field approximation to GR. The dominant operator in the weak field equation of GR is thus the d’Alembert (wave) operator, which has a retarded potential solution. Galaxies are huge physical systems with dimensions of many tens of thousands of light years. Thus, any change at the galactic center will be noticed at the rim only tens of thousands of years later. Those retardation effects are neglected in the present day galactic modelling used to calculate rotational velocities of matter in the rims of the galaxy and surrounding gas. The significant differences between the predictions of Newtonian instantaneous action at a distance and observed velocities are usually explained by either assuming dark matter or by modifying the laws of gravity (MOND). In this paper, we will show that, by taking general relativity seriously without neglecting retardation effects, one can explain the radial velocities of galactic matter in the M33 galaxy without postulating dark matter. It should be stressed that the current approach does not require that velocities v are high; in fact, the vast majority of galactic bodies (stars, gas) are substantially subluminal—in other words, the ratio of vc≪1. Typical velocities in galaxies are 100 km/s, which makes this ratio 0.001 or smaller. However, one should consider the fact that every gravitational system, even if it is made of subluminal bodies, has a retardation distance, beyond which the retardation effect cannot be neglected. Every natural system, such as stars and galaxies and even galactic clusters, exchanges mass with its environment, for example, the sun loses mass through solar wind and galaxies accrete gas from the intergalactic medium. This means that all natural gravitational systems have a finite retardation distance. The question is thus quantitative: how large is the retardation distance? For the M33 galaxy, the velocity curve indicates that the retardation effects cannot be neglected beyond a certain distance, which was calculated to be roughly 14,000 light years; similar analysis for other galaxies of different types has shown similar results. We demonstrate, using a detailed model, that this does not require a high velocity of gas or stars in or out of the galaxy and is perfectly consistent with the current observational knowledge of galactic and extra galactic material content and dynamics. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
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164 pages, 9428 KiB  
Article
:THE COSMOLOGICAL OTOC: Formulating New Cosmological Micro-Canonical Correlation Functions for Random Chaotic Fluctuations in Out-Of-Equilibrium Quantum Statistical Field Theory
by Sayantan Choudhury
Symmetry 2020, 12(9), 1527; https://doi.org/10.3390/sym12091527 - 16 Sep 2020
Cited by 37 | Viewed by 4050
Abstract
The out-of-time-ordered correlation (OTOC) function is an important new probe in quantum field theory which is treated as a significant measure of random quantum correlations. In this paper, using for the first time the slogan “Cosmology meets Condensed Matter Physics”, we demonstrate a [...] Read more.
The out-of-time-ordered correlation (OTOC) function is an important new probe in quantum field theory which is treated as a significant measure of random quantum correlations. In this paper, using for the first time the slogan “Cosmology meets Condensed Matter Physics”, we demonstrate a formalism to compute the Cosmological OTOC during the stochastic particle production during inflation and reheating following the canonical quantization technique. In this computation, two dynamical time scales are involved—out of them, at one time scale, the cosmological perturbation variable, and for the other, the canonically conjugate momentum, is defined, which is the strict requirement to define the time scale-separated quantum operators for OTOC and is perfectly consistent with the general definition of OTOC. Most importantly, using the present formalism, not only one can study the quantum correlation during stochastic inflation and reheating, but can also study quantum correlation for any random events in Cosmology. Next, using the late time exponential decay of cosmological OTOC with respect to the dynamical time scale of our universe which is associated with the canonically conjugate momentum operator in this formalism, we study the phenomenon of quantum chaos by computing the expression for the Lyapunov spectrum. Furthermore, using the well known Maldacena Shenker Stanford (MSS) bound on the Lyapunov exponent, λ≤2π/β, we propose a lower bound on the equilibrium temperature, T=1/β, at the very late time scale of the universe. On the other hand, with respect to the other time scale with which the perturbation variable is associated, we find decreasing, but not exponentially decaying, behaviour, which quantifies the random quantum correlation function out-of-equilibrium. We have also studied the classical limit of the OTOC and checked the consistency with the large time limiting behaviour of the correlation. Finally, we prove that the normalized version of OTOC is completely independent of the choice of the preferred definition of the cosmological perturbation variable. Full article
(This article belongs to the Special Issue New Advances of Cosmology and Astrophysics)
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