COSMIC TIME IN QUANTUM COSMOLOGY: INFLATION-COMPACTIFICATION AS A QUANTUM EFFECT

1993 ◽  
Vol 02 (02) ◽  
pp. 221-247 ◽  
Author(s):  
E.I. GUENDELMAN ◽  
A.B. KAGANOVICH
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Quantum Effect ◽  
Cosmic Time ◽  
Expectation Values ◽  
Cosmological Singularity ◽  
Inflationary Phase ◽  
Definition Of ◽  
The Universe ◽  
Kaluza Klein

We consider 1+D-dimensional, toroidally compact Kaluza-Klein theories. In the context of the minisuperspace approach of quantum cosmology, we solve the Wheeler-DeWitt equation in the presence of a negative cosmological constant and dust. Then, it is found that the quantum effects stabilize the volume of the Universe, so that there can be an avoidance of the cosmological singularity. Although cosmic time does not appear explicitly in the Wheeler-DeWitt equation, we find that a cosmic time dependence appears for the expectation values of certain variables. This result is obtained when proper care of some subtle points concerning the definition of averages in this model is taken. The stabilization of the volume, when there is anisotropy in the evolution of the Universe (which turns out to be quantized), is consistent with another effect we find: the existence of a “quantum inflationary phase” for some dimensions and simultaneously the existence of a “quantum deflationary contraction” for the rest.

DILATON INDUCED QUANTUM INFLATION-COMPACTIFICATION AND POSSIBILITY OF TRANSITION TO CLASSICAL ERA

1994 ◽  
Vol 09 (13) ◽  
pp. 1141-1150 ◽  
Author(s):  
E.I. GUENDELMAN ◽  
A.B. KAGANOVICH
Keyword(s):  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Cosmic Time ◽  
Higher Dimensions ◽  
Classical Description ◽  
Negative Cosmological Constant ◽  
Inflationary Phase ◽  
Superstring Theories

In many interesting models, including superstring theories, a vacuum with negative cosmological constant is predicted. For quantum cosmology (in higher dimensions) in the presence of coherent dilaton excitations and a negative cosmological constant, the role of cosmic time can be understood and we can then predict the existence of a “quantum inflationary phase” for some dimensions and a simultaneous “quantum deflationary phase” for the remaining dimensions. We discuss qualitatively how it may be possible to exit from this inflation-compactification era and give an example which involves a transition to a phase with zero cosmological constant which allows a classical description at late times.

EARLY HOMOGENEOUS UNIVERSE WITH VARIABLE COSMOLOGICAL CONSTANT: KINEMATICS TESTS

2007 ◽  
Vol 22 (13) ◽  
pp. 2415-2431 ◽  
Author(s):  
C. P. SINGH
Keyword(s):  
Cosmological Constant ◽  
Cosmic Time ◽  
Field Equations ◽  
Variable Cosmological Constant ◽  
Angular Diameter Distance ◽  
Proper Distance ◽  
Inflationary Phase ◽  
Homogeneous Universe ◽  
Gamma Law ◽  
The Look

A spatially homogeneous cosmological model with flat geometry filled with perfect fluid is studied in the presence of a variable cosmological "constant." Einstein's field equations are solved by using the "gamma-law" equation of state p = (γ-1)ρ, where the adiabatic parameter γ, varies with cosmic time. The functional form of γ, which is assumed to be the function of scale factor R as proposed by Carvalho, is used to describe the early evolution of universe with variable cosmological "constant." A unified description of early universe is given in which an inflationary phase is followed by radiation-dominated phase. It has been observed that the solutions are compatible with the result of recent observations. Exact expressions for the look-back time, proper distance, luminosity distance and angular diameter distance versus redshift are derived and their meaning are discussed in detail. The various physical aspects of the models are also discussed.

scholarly journals EMERGENT UNIVERSE WITH EXOTIC MATTER IN LOOP QUANTUM COSMOLOGY, DGP BRANE-WORLD AND KALUZA–KLEIN COSMOLOGY

2012 ◽  
Vol 27 (33) ◽  
pp. 1250189 ◽  
Author(s):  
PRABIR RUDRA
Keyword(s):  
Scalar Field ◽  
Quantum Cosmology ◽  
Brane World ◽  
Loop Quantum Cosmology ◽  
Tachyonic Field ◽  
Normal Matter ◽  
Emergent Scenario ◽  
Phantom Scalar ◽  
The Universe ◽  
Kaluza Klein

In this work we have investigated the emergent scenario of the Universe described by loop quantum cosmology model, DGP brane model and Kaluza–Klein cosmology. Scalar field along with barotropic fluid as normal matter is considered as the matter content of the Universe. In loop quantum cosmology it is found that the emergent scenario is realized with the imposition of some conditions on the value of the density of normal matter in case of normal and phantom scalar field. This is a surprising result indeed considering the fact that scalar field is the dominating matter component! In case of tachyonic field, emergent scenario is realized with some constraints on the value of ρ1 for both normal and phantom tachyon. In case of DGP brane-world realization of an emergent scenario is possible almost unconditionally for normal and phantom fields. Plots and table have been generated to testify this fact. In case of tachyonic field emergent scenario is realized with some constraints on [Formula: see text]. In Kaluza–Klein cosmology emergent scenario is possible only for a closed Universe in case of normal and phantom scalar field. For a tachyonic field, realization of emergent Universe is possible for all models (closed, open and flat).

scholarly journals ON THE TOPOLOGICAL NATURE OF THE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 18 ◽  
pp. 109-114
Author(s):  
M. D. MAIA
Keyword(s):  
General Relativity ◽  
Cosmological Constant ◽  
Cosmic Radiation ◽  
Cosmic Time ◽  
Space Time ◽  
Time Flow ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Topological Changes

It is shown that topological changes in space-time are necessary to make General Relativity compatible with the Newtonian limit and to solve the hierarchy of the fundamental interactions. We detail how topology and topological changes appear in General Relativity and how it leaves an observable footprint in space-time. In cosmology we show that such topological observable is the cosmic radiation produced by the acceleration of the universe. The cosmological constant is a very particular case which occurs when the expansion of the universe into the vacuum occurs only in the direction of the cosmic time flow.

ON THE COSMOLOGICAL CONSTANT IN QUANTUM COSMOLOGY OF THE BRANS–DICKE THEORY

1998 ◽  
Vol 13 (17) ◽  
pp. 1333-1337 ◽  
Author(s):  
ZONG-HONG ZHU ◽  
YUAN-ZHONG ZHANG ◽  
XIANG-PING WU
Keyword(s):  
Boundary Condition ◽  
Wave Function ◽  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Gravitational Theory ◽  
Wkb Approximation ◽  
Expanding Universe ◽  
The Universe

We study the issue of the cosmological constant in quantum cosmology combined with the Brans–Dicke gravitational theory. Using the minisuperspace approximation, we build up the Wheeler–De Witt equation and then obtain the wave function of the universe by further assuming the WKB approximation under the boundary condition proposed by Vilenkin. It is shown that the amplitude of the resulting wave function, which represents an expanding universe, reaches its peaks if the cosmological constant vanishes.

scholarly journals HYBRID QUANTUM COSMOLOGY: COMBINING LOOP AND FOCK QUANTIZATIONS

2009 ◽  
Vol 24 (15) ◽  
pp. 2820-2838 ◽  
Author(s):  
G. A. MENA MARUGÁN ◽  
M. MARTÍN-BENITO
Keyword(s):  
Quantum Cosmology ◽  
Degrees Of Freedom ◽  
Loop Quantum Cosmology ◽  
Cosmological Singularity ◽  
Internal Time ◽  
Gravitational Model ◽  
Spatial Topology ◽  
Linearly Polarized ◽  
Definition Of ◽  
Physical Consequences

As a necessary step towards the extraction of realistic results from Loop Quantum Cosmology, we analyze the physical consequences of including inhomogeneities. We consider in detail the quantization of a gravitational model in vacuo which possesses local degrees of freedom, namely, the linearly polarized Gowdy cosmologies with the spatial topology of a three-torus. We carry out a hybrid quantization which combines loop and Fock techniques. We discuss the main aspects and results of this hybrid quantization, which include the resolution of the cosmological singularity, the polymeric quantization of the internal time, a rigorous definition of the quantum constraints and the construction of their solutions, the Hilbert structure of the physical states, and the recovery of a conventional Fock quantization for the inhomogeneities.

scholarly journals Time in Quantum Cosmology

Universe ◽  
2022 ◽  
Vol 8 (1) ◽  
pp. 36
Author(s):  
Claus Kiefer ◽  
Patrick Peter
Keyword(s):  
Quantum Gravity ◽  
Quantum Cosmology ◽  
Main Application ◽  
Definition Of ◽  
The Universe ◽  
Quantum Geometrodynamics

Time in quantum gravity is not a well-defined notion despite its central role in the very definition of dynamics. Using the formalism of quantum geometrodynamics, we briefly review the problem and illustrate it with two proposed solutions. Our main application is quantum cosmology—the application of quantum gravity to the Universe as a whole.

“Stationary” Schrödinger equation in quantum cosmology

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040040
Author(s):  
N. Gorobey ◽  
A. Lukyanenko ◽  
A. Shavrin
Keyword(s):  
Energy Density ◽  
Quantum Cosmology ◽  
Quantum Dynamics ◽  
Harmonic Approximation ◽  
Cosmic Time ◽  
Positive Functional ◽  
The Universe ◽  
Principle Of Extremum ◽  
Extremum Conditions

The conditional principle of extremum in quantum cosmology is formulated for a positive functional of the energy density of space, in which gravitational constraints serve as additional conditions. The extremum conditions determine the discrete spectrum of the “stationary” state of the universe with the corresponding values of the energy density of space. A dynamic interpretation of solutions is proposed, in which the quantum number of the energy density plays the role of cosmic time. In the self-consistent harmonic approximation, the quantum dynamics of the anisotropic model of the Bianchi IX universe is considered.

scholarly journals CONSTRAINTS ON DARK ENERGY FROM THE OBSERVED EXPANSION OF OUR COSMIC HORIZON

2009 ◽  
Vol 18 (07) ◽  
pp. 1113-1127 ◽  
Author(s):  
FULVIO MELIA
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmic Time ◽  
Accelerating Universe ◽  
De Sitter ◽  
Dark Energy Component ◽  
The Standard Model ◽  
Type Ia ◽  
Age Of The Universe ◽  
The Universe

Within the context of standard cosmology, an accelerating universe requires the presence of a third "dark" component of energy, beyond matter and radiation. The available data, however, 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 cosmological expansion in terms of observer-dependent coordinates, in addition to the more conventional comoving coordinates. This procedure explicitly reveals the role played by the radius Rh of our cosmic horizon in the interrogation of the data. (In Rindler's notation, Rh coincides with the "event horizon" in the case of de Sitter, but changes in time for other cosmologies that also contain matter and/or radiation.) With this approach, we show that the interpretation of dark energy as a cosmological constant is clearly disfavored by the observations. Within the framework of standard Friedmann–Robertson–Walker cosmology, we derive an equation describing the evolution of Rh, and solve it using the WMAP and Type Ia supernova data. In particular, we consider the meaning of the observed equality (or near-equality) Rh(t0) ≅ ct0, where t0 is the age of the universe. This empirical result is far from trivial, for a cosmological constant would drive Rh(t) toward ct (t is the cosmic time) only once — and that would have to occur right now. Though we are not here espousing any particular alternative model of dark energy, for comparison we also consider scenarios in which dark energy is given by scaling solutions, which simultaneously eliminate several conundrums in the standard model, including the "coincidence" and "flatness" problems, and account very well for the fact that Rh(t0) ≈ ct0.

scholarly journals A Universe that Does Not Know the Time

Universe ◽  
2019 ◽  
Vol 5 (3) ◽  
pp. 84 ◽  
Author(s):  
João Magueijo ◽  
Lee Smolin
Keyword(s):  
Cosmological Constant ◽  
Time Line ◽  
Cosmological Time ◽  
Quantum Time ◽  
Machine Cycle ◽  
Classical Behaviour ◽  
Quantum Operators ◽  
Definition Of ◽  
Chern Simons ◽  
The Universe

In this paper, we propose that cosmological time is a quantum observable that does not commute with other quantum operators essential for the definition of cosmological states, notably the cosmological constant. This is inspired by properties of a measure of time—the Chern–Simons time—and the fact that in some theories it appears as a conjugate to the cosmological constant, with the two promoted to non-commuting quantum operators. Thus, the Universe may be “delocalised” in time: it does not know the time, a property which opens up new cosmological scenarios, as well as invalidating several paradoxes, such as the timelike tower of turtles associated with an omnipresent time line. Alternatively, a Universe with a sharply defined clock time must have an indeterminate cosmological constant. The challenge then is to explain how islands of localized time may emerge, and give rise to localized histories. In some scenarios, this is achieved by backward transitions in quantum time, cycling the Universe in something akin to a time machine cycle, with classical flow and quantum ebbing. The emergence of matter in a sea of Lambda probably provides the ballast behind classical behaviour.

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