scholarly journals Running of effective dimension and cosmological entropy in early universe

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Yong Xiao
Keyword(s):  
Quantum Gravity ◽  
Early Universe ◽  
The State ◽  
Two Dimensional ◽  
Effective Dimension ◽  
Particle Horizon ◽  
Higher Dimensional ◽  
Energetic State ◽  
The Universe

AbstractIn this paper, we suggest that the early universe starts from a high-energetic state with a two dimensional description and the state recovers to be four dimensional when the universe evolves into the radiation dominated phase. This scenario is consistent with the recent viewpoint that quantum gravity should be effectively two dimensional in the ultraviolet and recovers to be four dimensional in the infrared. A relationship has been established between the running of effective dimension and that of the entropy inside particle horizon of the universe, i.e., as the effective dimension runs from two to four, the corresponding entropy runs from the holographic entropy to the normal entropy appropriate to radiation. These results can be generalized to higher dimensional cases.

scholarly journals ACCELERATION AND DECELERATION IN THE CURVATURE-INDUCED PHANTOM MODEL OF THE LATE AND FUTURE UNIVERSE: COSMIC COLLAPSE AND ITS QUANTUM ESCAPE

2009 ◽  
Vol 18 (05) ◽  
pp. 865-887
Author(s):  
S. K. SRIVASTAVA ◽  
J. DUTTA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Early Universe ◽  
High Energy ◽  
High Energy Density ◽  
Energy Models ◽  
Acceleration And Deceleration ◽  
The Universe

In this paper, the cosmology of the late and future universe is obtained from f(R) gravity with nonlinear curvature terms R2 and R3 (R is the Ricci scalar curvature). It is different from f(R) dark energy models where nonlinear curvature terms are taken as a gravitational alternative to dark energy. In the present model, neither linear nor nonlinear curvature terms are taken as dark energy. Rather, dark energy terms are induced by curvature terms and appear in the Friedmann equation derived from f(R) gravitational equations. This approach has an advantage over f(R) dark energy models in three ways: (i) results are consistent with WMAP observations, (ii) dark matter is produced from the gravitational sector and (iii) the universe expands as ~ t2/3 during dominance of the curvature-induced dark matter, which is consistent with the standard cosmology. Curvature-induced dark energy mimics phantom and causes late acceleration. It is found that transition from matter-driven deceleration to acceleration takes place at the redshift 0.36 at time 0.59 t0 (t0 is the present age of the universe). Different phases of this model, including acceleration and deceleration during the phantom phase, are investigated. It is found that expansion of the universe will stop at the age of 3.87 t0 + 694.4 kyr. After this epoch, the universe will contract and collapse by the time of 336.87 t0 + 694.4 kyr. Further, it is shown that cosmic collapse obtained from classical mechanics can be avoided by making quantum gravity corrections relevant near the collapse time due to extremely high energy density and large curvature analogous to the state of the very early universe. Interestingly, the cosmological constant is also induced here; it is extremely small in the classical domain but becomes very high in the quantum domain. This result explains the largeness of the cosmological constant in the early universe due to quantum gravity effects during this era and its very low value in the present universe due to negligible quantum effect in the late universe.

NUCLEON PROPERTIES IN THE EXPANDING UNIVERSE

2003 ◽  
Vol 18 (02n06) ◽  
pp. 374-383
Author(s):  
W-Y. PAUCHY HWANG
Keyword(s):  
Phase Transition ◽  
Early Universe ◽  
Mass Formula ◽  
The State ◽  
Nucleon Mass ◽  
Expanding Universe ◽  
Qcd Phase Transition ◽  
Qcd Vacuum ◽  
The Universe

Our universe expands and cools. The electroweak (EW) phase transition, which endows masses to the various particles, and QCD phase transition, which gives rise to confinement of quarks and gluons within hadrons in the true QCD vacuum, Would presumably have taken place in the early universe, respectively, at around 10-11 sec and at a time between 10-5 sec and 10-4 sec, or at the temperature of about 300 GeV and of about 150 MeV, respectively. It is clear that the nucleon mass [Formula: see text], the axial coupling [Formula: see text], and other nucleon parameters evolve as the universe evolves, thereby serving as an important gauge for understanding the state of the Universe.

scholarly journals Quantum Gravity as Higher Dimensional Perspective

2016 ◽  
Vol 8 (4) ◽  
pp. 38
Author(s):  
Rob Langley
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Single Point ◽  
Planck Scale ◽  
Conceptual Structure ◽  
The State ◽  
Mathematical Principle ◽  
Vanishing Points ◽  
Higher Dimensional ◽  
Single State

Although highly predictive in their respective macroscopic and microscopic domains of applicability, General Relativity and quantum mechanics are mathematically incompatible, perhaps most markedly in assumptions in their formalisms concerning the nature of space and time. In <em>perspective</em> we already have a conceptual structure that links the local, macroscopic frame and the remote, apparently microscopic frame. A mathematical principle is invoked as a natural limit on D(n), so that effects which are clearly perspectival at D=3 become ‘more real’ (<em>effectively</em> observer-independent) with each D(n) increment. For instance, the apparently microscopic becomes the effectively microscopic and <em>scale extremes are juxtaposed</em>, so that black holes are local, macroscopic vanishing-points, in a similar way to that in which in projective geometry the point at infinity is incorporated into the foreground.  (In other words, <em>a black hole is a blown-up ‘Planck-scale’ singularity</em>.) Characteristics of the earthbound frame are applied to D&gt;3, suggesting a physical basis for entanglement, and perspectival interpretations of quantum gravity, dimensional reduction and the information paradox.  We claim that the familiar processes whereby multiple physical states become describable by a single state in which composition information appears to be lost (e.g., ‘falling into a black hole’, the state of quantum linearity, and the state of freefall) are all examples of effective convergence of a space or <em>n</em>-surface to a single point of perspective.

scholarly journals ON INHOMOGENEITY OF A STRING BIT MODEL FOR QUANTUM GRAVITY

2005 ◽  
Vol 14 (09) ◽  
pp. 1545-1560 ◽  
Author(s):  
C.-W. H. LEE ◽  
R. B. MANN
Keyword(s):  
Quantum Gravity ◽  
Gravitational Effect ◽  
Two Dimensional ◽  
Open Universe ◽  
The Universe

We study quantum gravitational effect on a two-dimensional open universe with one particle by means of a string bit model. We find that matter is necessarily homogeneously distributed if the influence of the particle on the size of the universe is optimized.

The Physical State of the Universe in the Planck Era

2018 ◽  
Vol 73 (6) ◽  
pp. 533-537 ◽  
Author(s):  
Peter J. Riggs
Keyword(s):  
Quantum Gravity ◽  
Early Universe ◽  
Mathematical Description ◽  
Physical State ◽  
Full Theory ◽  
Low Entropy ◽  
The Universe

AbstractThe Planck Era cannot be given an accurate mathematical description until the full theory of quantum gravity is available. However, some aspects of the physical state of the Planck Era can be revealed by order of the magnitude considerations which also have implications for the low entropy of the very early universe.

scholarly journals Schrödinger evolution of two-dimensional black holes

2021 ◽  
Vol 2021 (12) ◽  
Author(s):  
Steven B. Giddings
Keyword(s):  
Black Holes ◽  
Higher Dimensions ◽  
The State ◽  
Classical Solutions ◽  
Two Dimensional ◽  
Higher Dimensional ◽  
Starting Point ◽  
Gravity Effects ◽  
Quantum Treatment ◽  
Time Slicing

Abstract This paper systematically treats the evolving quantum state for two-dimensional black holes, with particular focus on the CGHS model, but also elucidating features generalizing to higher dimensions. This is done in Schrödinger picture(s), to exhibit the dynamic evolution of the state at intermediate times. After a review of classical solutions, also connecting to descriptions of higher-dimensional black holes, it overviews the canonical quantum treatment of the full evolution, including gravitational dynamics. Derived in an approximation to this, following conversion to “perturbation picture”, is the evolution of the quantum matter on the background geometry. Features of the evolving matter state are described, based on choice of a time slicing to put the evolution into ADM form. The choices of slicing as well as coordinates on the slices result in different quantum “pictures” for treating the evolution. If such a description is based on smooth trans-horizon slices, that avoids explicit reference to ultra-planckian modes familiar from traditional treatments, and exhibits the Hawking excitations as emerging from a “quantum atmosphere” with thickness comparable to the inverse temperature. Detailed study of the state exhibits the entanglement structure between Hawking quanta and the partner excitations inside the black hole, and the corresponding “missing information”. This explicit description also allows direct study of the evolution and features, e.g. as seen by infalling observers, of these partner excitations, helping to address various puzzles with them. Explicit treatment of the evolving state, and its extension to higher dimensions, provides further connections to information theory and a starting point for study of corrections that can unitarize evolution, arising from new quantum gravity effects — whether wormholes or something entirely different.

scholarly journals Space, Matter and Interactions in a Quantum Early Universe Part I: Kac–Moody and Borcherds Algebras

Symmetry ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 2342
Author(s):  
Piero Truini ◽  
Alessio Marrani ◽  
Michael Rios ◽  
Klee Irwin
Keyword(s):  
Quantum Gravity ◽  
Lie Algebra ◽  
Early Universe ◽  
Quantum Model ◽  
Initial Condition ◽  
Particle Interactions ◽  
Early Stages ◽  
The Universe ◽  
Expansion Of Space ◽  
Matter And Interactions

We introduce a quantum model for the universe at its early stages, formulating a mechanism for the expansion of space and matter from a quantum initial condition, with particle interactions and creation driven by algebraic extensions of the Kac–Moody Lie algebra e9. We investigate Kac–Moody and Borcherds algebras, and we propose a generalization that meets further requirements that we regard as fundamental in quantum gravity.

scholarly journals Antisymmetric Tensor Fields in Modified Gravity: A Summary

Symmetry ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 1573
Author(s):  
Tanmoy Paul
Keyword(s):  
Energy Density ◽  
Early Universe ◽  
Evolutionary Process ◽  
Field Energy ◽  
Modified Theories Of Gravity ◽  
Tensor Fields ◽  
Curvature Term ◽  
Higher Dimensional ◽  
Present Universe ◽  
The Universe

We provide various aspects of second rank antisymmetric Kalb–Ramond (KR) field in modified theories of gravity. The KR field energy density is found to decrease with the expansion of our universe at a faster rate in comparison to radiation and matter components. Thus as the universe evolves and cools down, the contribution of the KR field on the evolutionary process reduces significantly, and at present it almost does not affect the universe evolution. However the KR field has a significant contribution during early universe; in particular, it affects the beginning of inflation as well as increases the amount of primordial gravitational radiation and hence enlarges the value of tensor-to-scalar ratio in respect to the case when the KR field is absent. In regard to the KR field couplings, it turns out that in four dimensional higher curvature inflationary model the couplings of the KR field to other matter fields is given by 1/MPl (where MPl is known as the “reduced Planck mass” defined by MPl=18πG with G is the “Newton’s constant”) i.e., same as the usual gravity–matter coupling; however in the context of higher dimensional higher curvature model the KR couplings get an additional suppression over 1/MPl. Thus in comparison to the four dimensional model, the higher curvature braneworld scenario gives a better explanation of why the present universe carries practically no footprint of the Kalb–Ramond field. The higher curvature term in the higher dimensional gravitational action acts as a suitable stabilizing agent in the dynamical stabilization mechanism of the extra dimensional modulus field from the perspective of effective on-brane theory. Based on the evolution of KR field, one intriguing question can be—“sitting in present day universe, how do we confirm the existence of the Kalb–Ramond field which has considerably low energy density (with respect to the other components) in our present universe but has a significant impact during early universe?” We try to answer this question by the phenomena “cosmological quantum entanglement” which indeed carries the information of early universe. Finally, we briefly discuss some future perspectives of Kalb–Ramond cosmology at the end of the paper.

scholarly journals Black Holes in the Early Universe

1974 ◽  
Vol 64 ◽  
pp. 184-184
Author(s):  
Bernard J. Carr ◽  
Stephen W. Hawking
Keyword(s):  
Black Holes ◽  
Early Universe ◽  
Gravitational Collapse ◽  
Radiation Pressure ◽  
Initial Conditions ◽  
Particle Horizon ◽  
The Universe

The existence of galaxies indicates that the early universe must have been inhomogeneous and might have been highly chaotic. This could have lead to regions of the size of the particle horizon undergoing gravitational collapse to produce black holes with initial masses from 10-5 g upwards. Radiation pressure in the early Universe would cause these black holes to grow by accretion. However, despite previous expectations, this accretion would not be very much unless the initial conditions of the Universe were arranged in a special and a causal manner. Observations indicate that, at the most, only a small fraction of the matter in the early Universe can have undergone gravitational collapse.

scholarly journals IMPLICATIONS OF A QUANTUM MECHANICAL TREATMENT OF THE UNIVERSE

1998 ◽  
Vol 13 (05) ◽  
pp. 347-351 ◽  
Author(s):  
MURAT ÖZER
Keyword(s):  
Quantum Mechanics ◽  
Wave Packet ◽  
Early Universe ◽  
Mechanical Treatment ◽  
Correspondence Principle ◽  
Scale Factor ◽  
Quantum Mechanical ◽  
Quantum Mechanical Treatment ◽  
The Standard Model ◽  
The Universe

We attempt to treat the very early Universe according to quantum mechanics. Identifying the scale factor of the Universe with the width of the wave packet associated with it, we show that there cannot be an initial singularity and that the Universe expands. Invoking the correspondence principle, we obtain the scale factor of the Universe and demonstrate that the causality problem of the standard model is solved.

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