scholarly journals Anisotropic quantum cosmology with minimally coupled scalar field

2019 ◽  
Vol 34 (34) ◽  
pp. 1950283 ◽  
Author(s):  
Saumya Ghosh ◽  
Sunandan Gangopadhyay ◽  
Prasanta K. Panigrahi
Keyword(s):  
Scalar Field ◽  
Wave Packet ◽  
Quantum Cosmology ◽  
Hamiltonian Formalism ◽  
Big Bang ◽  
Type I ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

In this paper, we perform the Wheeler–DeWitt quantization for Bianchi type I anisotropic cosmological model in the presence of a scalar field minimally coupled to the Einstein–Hilbert gravity theory. We also consider the cosmological (perfect) fluid to construct the matter sector of the model whose dynamics plays the role of time. After obtaining the Wheeler–DeWitt equation from the Hamiltonian formalism, we then define the self-adjointness relations properly. Doing that, we proceed to get a solution for the Wheeler–DeWitt equation and construct a well-behaved wave function for the universe. The wave packet is next constructed from a superposition of the wave functions with different energy eigenvalues together with a suitable weight factor which renders the norm of the wave packet finite. It is then concluded that the Big-Bang singularity can be removed in the context of quantum cosmology.

scholarly journals Preinflationary Dynamics of Power-Law Potential in Loop Quantum Cosmology †

Universe ◽  
2018 ◽  
Vol 4 (8) ◽  
pp. 87 ◽  
Author(s):  
M. Shahalam
Keyword(s):  
Quantum Cosmology ◽  
Initial Conditions ◽  
Big Bang ◽  
Loop Quantum Cosmology ◽  
Inflationary Universe ◽  
Slow Roll ◽  
Wide Range ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity

In this article, I mainly discuss the dynamics of the pre-inflationary Universe for the potential V ( ϕ ) ∝ ϕ n with n = 5 / 3 in the context of loop quantum cosmology, in which the big bang singularity is resolved by a non-singular quantum bounce. In the case of the kinetic energy-dominated initial conditions of the scalar field at the bounce, the numerical evolution of the Universe can be split up into three regimes: bouncing, transition, and slow-roll inflation. In the bouncing regime, the numerical evolution of the scale factor does not depend on a wide range of initial values, or on the inflationary potentials. I calculate the number of e-folds in the slow-roll regime, by which observationally identified initial conditions are obtained. Additionally, I display the phase portrait for the model under consideration.

scholarly journals Cosmology at the top of the α′ tower

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Jerome Quintin ◽  
Heliudson Bernardo ◽  
Guilherme Franzmann
Keyword(s):  
Energy Condition ◽  
Big Bang ◽  
Null Energy Condition ◽  
Einstein Frame ◽  
Accelerated Expansion ◽  
De Sitter ◽  
The Big Bang ◽  
Big Bang Singularity ◽  
Matter Sector

Abstract The cosmology of the fully α′-corrected duality-invariant action for the Neveu-Schwarz sector of string theory is revisited, with special emphasis on its coupling to matter sources. The role of the duality covariant pressure and dilatonic charge of the matter sector is explored in various contexts, from the low-curvature regime to non-perturbative solutions in α′. We comment on how an infinite tower of α′ corrections allows for fixed-dilaton de Sitter solutions, even in vacuum. We further investigate the necessary conditions for accelerated expansion in the Einstein frame, as well as for non-singular bounces that could resolve the big bang singularity. In particular, explicit examples are constructed, which show that the tower of α′ corrections may support an Einstein-frame non-singular cosmological bouncing background, even when the matter sector respects the null energy condition.

Hamiltonian Formalism of Bianchi Type I Model for Fluid Bulk and Shearing Viscosity

2021 ◽  
Author(s):  
Shouvik Sadhukhan ◽  
Alokananda Kar
Keyword(s):  
Scalar Field ◽  
Viscous Fluid ◽  
Bianchi Type ◽  
Hamiltonian Formalism ◽  
Big Bang ◽  
Type I ◽  
Scale Factors ◽  
Anisotropic Expansion ◽  
Large Anisotropy

In this paper we will consider the cosmic fluid to be dissipating i.e it has both bulk and shearing viscosity. We propose the Hamiltonian formalism of Bianchi type 1 cosmological model for cosmic fluid which is dissipating i.e it has both shearing and bulk viscosity. We have considered both the equation of state parameter ω and the cosmological constant Λ as the function of volume V(t) which is defined by the product of three scale factors of the Bianchi type 1 line element. We propose a Lagrangian for the anisotropic Bianchi type-1 model in view of a variable mass moving in a variable potential . We can decompose the anisotropic expansion of Bianchi type 1 in terms of expansion and shearing motion by Lagrangian mechanism. We have considered a canonical transformation from expanding scale factor to scalar field ø which helps us to give the proper classical definition of that scalar field in terms of scale factors of the mentioned model. By this transformation we can express the mass to be moving in a scalar potential field. This definition helps us to explain the nature of expansion of universe during cosmological inflation. We have used large anisotropy(as in the cases of Bianchi models) and proved that cosmic inflation is not possible in such large anisotropy. Therefore we can conclude that the extent of anisotropy is less in case of our universe. Otherwise the inflation theory which explained the limitations of Big Bang cannot be resolved. In the case of bulk and shearing viscous fluid we get the solution of damped harmonic oscillator after the cosmological inflation.Part I contains the calculations of bulk viscous fluids and Part II contains the calculations of bulk and shearing viscous fluid.At the end we have also provided the relation of shearing and expansion.Part III will give the approximation of low viscosity to solve the viscous fluid problem.

scholarly journals Limitations of Observational Cosmology

1990 ◽  
Vol 123 ◽  
pp. 543-550
Author(s):  
Menas Kafatos
Keyword(s):  
Theoretical Models ◽  
Big Bang ◽  
Theoretical Physics ◽  
Observational Cosmology ◽  
Observable Universe ◽  
Fundamental Properties ◽  
Distant Galaxies ◽  
The Big Bang ◽  
The Universe

AbstractUnlike the usual situation with theoretical physics which is testable in the laboratory, in cosmological theories of the universe one faces the following problems: The observer is part of the system, the universe, and this system cannot be altered to test physical theory. Even though one can in principle consider any part of the observable universe as separate from the acts of observation, the very hypothesis of big bang implies that in the distant past, space-time regions containing current observers were part of the same system. One, therefore, faces a situation where the observer has to be considered as inherently a part of the entire system. The existence of horizons of knowledge in any cosmological view of the universe is then tantamount to inherent observational limits imposed by acts of observation and theory itself. For example, in the big bang cosmology the universe becomes opaque to radiation early on, and the images of extended distant galaxies merge for redshifts, z, of the order of a few. Moreover, in order to measure the distance of a remote galaxy to test any cosmological theory, one has to disperse its light to form a spectrum which would cause confusion with other background galaxies. Since the early universe should be described in quantum terms, it follows that the same problems regarding quantum reality and the role of the observer apply to the universe as a whole. One of the most fundamental properties of quantum theory, non-locality, may then apply equally well to the universe. Some of the problems facing big bang cosmology, like the horizon and flatness problems, may not then be preconditions on theoretical models but may instead be the manifestations of the quantum nature of the universe.

scholarly journals Invariant Bianchi type I models in f(R,T) gravity

2018 ◽  
Vol 15 (02) ◽  
pp. 1850026 ◽  
Author(s):  
Anil Kumar Yadav ◽  
Ahmad T. Ali
Keyword(s):  
Bianchi Type ◽  
Big Bang ◽  
Type I ◽  
Analysis Method ◽  
Field Equations ◽  
Bianchi Type I ◽  
Nonsingular Solution ◽  
The Big Bang ◽  
Big Bang Singularity ◽  
Special Case

In this paper, we search the existence of invariant solutions of Bianchi type I space-time in the context of [Formula: see text] gravity with special case [Formula: see text]. The exact solution of the Einstein’s field equations are derived by using Lie point symmetry analysis method that yield two models of invariant universe for symmetries [Formula: see text] and [Formula: see text]. The model with symmetries [Formula: see text] begins with big bang singularity while the model with symmetries [Formula: see text] does not favor the big bang singularity. Under this specification, we find out at set of singular and nonsingular solution of Bianchi type I model which present several other physically valid features within the framework of [Formula: see text] gravity.

scholarly journals Bouncing scalar field cosmology in the polymeric minisuperspace picture

2014 ◽  
Vol 29 (32) ◽  
pp. 1450169 ◽  
Author(s):  
B. Vakili ◽  
K. Nozari ◽  
V. Hosseinzadeh ◽  
M. A. Gorji
Keyword(s):  
Scalar Field ◽  
Symplectic Structure ◽  
Classical Model ◽  
Big Bang ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Polymeric Form ◽  
Quantum Operators ◽  
The Big Bang ◽  
Big Bang Singularity

We study a cosmological setup consisting of a FRW metric as the background geometry with a massless scalar field in the framework of classical polymerization of a given dynamical system. To do this, we first introduce the polymeric representation of the quantum operators. We then extend the corresponding process to reach a transformation which maps any classical variable to its polymeric counterpart. It is shown that such a formalism has also an analogue in terms of the symplectic structure, i.e. instead of applying polymerization to the classical Hamiltonian to arrive its polymeric form, one can use a new set of variables in terms of which Hamiltonian retains its form but now the corresponding symplectic structure gets a new deformed functional form. We show that these two methods are equivalent and by applying them to the scalar field FRW cosmology see that the resulting scale factor exhibits a bouncing behavior from a contraction phase to an expanding era. Since the replacing of the big bang singularity by a bouncing behavior is one of the most important predictions of the quantum cosmological theories, we may claim that our polymerized classical model brings with itself some signals from quantum theory.

Could God Have Made the Big Bang? (On Theistic Counterfactuals)

Dialogue ◽  
1994 ◽  
Vol 33 (1) ◽  
pp. 3-20
Author(s):  
Duncan Macintosh
Keyword(s):  
Big Bang ◽  
Will Emit ◽  
Initial States ◽  
Ex Nihilo ◽  
The Big Bang ◽  
The Universe ◽  
Big Bang Singularity ◽  
Infinite Temperature ◽  
P 53 ◽  
Better Than

That the universe began in a big bang is often believed by theists to confirm divine creation ex nihilo. But Quentin Smith claims that it means God must not exist. For if he does, there is an earliest state E of the universe. God made E. E is ensured either to contain animate creatures or to lead to an animate state. For God would know that an animate universe is better than an inanimate one, and that even a minimally morally good being would be obliged to create one if he could. And God, being at least minimally mor-ally good, and all-powerful, would be able and inclined to ensure the existence of one (p. 53). But science says that E is inanimate since the big bang singularity (E) involves the life-hostile conditions of infinite temperature, curvature and density; also that it is inherently unpredictable and lawless so that there is no guarantee it will emit particles that will evolve into an animate state. Thus £ is not ensured to lead to an animate state (p. 53), and thus God could not have made E. So, God does not exist (p. 54). Smith: “There are countless logically possible initial states of the universe that lead by a natural and law-like evolution to animate states and if God had created the universe he would have selected one of these” (p. 58).

AN OVERVIEW OF QUANTUM COSMOLOGY

1986 ◽  
Vol 01 (04) ◽  
pp. 887-912 ◽  
Author(s):  
L.Z. FANG ◽  
Z.C. WU
Keyword(s):  
Quantum Cosmology ◽  
Big Bang ◽  
Important Stage ◽  
Big Bang Model ◽  
Physical Laws ◽  
The Big Bang ◽  
The Universe

Hawking’s theory of quantum cosmology is the most important stage in understanding our universe since the big bang model. In principle, one can predict everything in the universe solely from physical laws. All main results within this framework have been reviewed in this paper.

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