Future state of the universe

Dąbrowski, Mariusz P.

doi:10.1002/andp.200510193

Cited by 20 publications

(9 citation statements)

References 67 publications

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“…If some gaseous stars (a galaxy) obey the γ-law (γ = 4/3), it may provide an alternative explanation about that, the timeperiodic solutions coincide with the expansion segment (the red-shift effect) in a short time. We notice that it is the significant difference between the traditional re-collapsing model with negative cosmological constant Λ < 0 [3].…”

Section: Discussionmentioning

confidence: 78%

Analytically periodic solutions to the three-dimensional Euler–Poisson equations of gaseous stars with a negative cosmological constant

Yuen¹

2009

Class. Quantum Grav.

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By the extension of the 3-dimensional analytical solutions of Goldreich and Weber [6] with adiabatic exponent γ = 4/3, to the (classical) Euler-Poisson equations without cosmological constant, the self-similar (almost re-collapsing) time-periodic solutions with negative cosmological constant (Λ < 0) are constructed. The solutions with time-periodicity are novel. On basing these solutions, the time-periodic and almost re-collapsing model is conjectured, for some gaseous stars.

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Section: Discussionmentioning

confidence: 78%

Analytically periodic solutions to the three-dimensional Euler–Poisson equations of gaseous stars with a negative cosmological constant

Yuen¹

2009

Class. Quantum Grav.

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“…Singularity theorems have been proven, with different assumptions, for instance in the context of inflaton fields which violate positive energy conditions [15]. Moreover, dropping positive energy assumptions does not necessarily improve the situation but usually makes it worse as the development of sudden future singularities in so-called phantom matter field models shows [16].…”

Section: Beyond General Relativitymentioning

confidence: 99%

Singularities and Quantum Gravity

Bojowald¹

2007

AIP Conference Proceedings

108

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Abstract.Although there is general agreement that a removal of classical gravitational singularities is not only a crucial conceptual test of any approach to quantum gravity but also a prerequisite for any fundamental theory, the precise criteria for non-singular behavior are often unclear or controversial. Often, only special types of singularities such as the curvature singularities found in isotropic cosmological models are discussed and it is far from clear what this implies for the very general singularities that arise according to the singularity theorems of general relativity. In these lectures we present an overview of the current status of singularities in classical and quantum gravity, starting with a review and interpretation of the classical singularity theorems. This suggests possible routes for quantum gravity to evade the devastating conclusion of the theorems by different means, including modified dynamics or modified geometrical structures underlying quantum gravity. The latter is most clearly present in canonical quantizations which are discussed in more detail. Finally, the results are used to propose a general scheme of singularity removal, quantum hyperbolicity, to show cases where it is realized and to derive intuitive semiclassical pictures of cosmological bounces. OVERVIEWPhysical theories are always idealizations without which the complexity of nature would be too great to fathom. Theoretical physics is, mostly very successfully, based on assumptions needed to formulate equations, find solutions and use them to describe, explain and further investigate physical phenomena.Sometimes, however, these assumptions may not be general enough for all purposes. When they are violated, the theory breaks down which mathematically appears as the development of singularities. An example is given by the use of continuous fields rather than discrete atomic structures in condensed matter physics. When fields vary too strongly on small length scales, such as in shock waves, singularities can occur in continuous field equations even though the basic, discrete physical description remains valid. Usually, deviations between solutions and observations increase before a mathematical singularity is reached. It is then clear that the approximate description can no longer be trusted beyond a certain point. But observations are not always available in such regimes where singularities are approached and an interpretation of mathematical singularities becomes more difficult. This is the case especially for gravity where observations of strong field regimes are lacking.Singularities in general relativity therefore play a special and dual role. First, the classical importance of singularities can be questioned since there are always assumptions behind special solutions or general theorems leading to singularities. But classical singularities in general relativity also provide an excellent chance to derive implications for the structure of space-time described by general relativity. When the theory breaks down, lesson...

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“…These singularities are similar to another type of singularity termed as Finite Density singularities which are spatial singularities and happen in inhomogeneous models of the Universe. It should be noted that an SFS can occur also in inhomogeneous models [5] where they violate all energy conditions [6]. The isotropy of the Universe is not a requirement for the occurrence of such singularities either and they may take place in anisotropic models as well [1].…”

Section: Sudden Future Singularity Modelsmentioning

confidence: 98%

Constraining sudden future singularity models

Ghodsi¹,

Hendry

2010

Annalen der Physik

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One of the key challenges facing cosmologists today is the nature of the mysterious dark energy introduced in the standard model of cosmology to account for the current accelerating expansion of the universe. In this regard, many other non‐standard cosmologies have been proposed which would eliminate the need to explicitly include any form of dark energy. One such model is the Sudden Future Singularity (SFS) model, in which no equation of state linking the energy density and the pressure in the universe is assumed to hold. In this model it is possible to have a blow up of the pressure occurring in the near future while the energy density would remain unaffected. The particular evolution of the scale factor of the Universe in this model that results in a singular behaviour of the pressure also admits acceleration in the current era as required. In this paper we compare an example SFS model with the current data from high redshift supernovae, baryon acoustic oscillations (BAO) and the cosmic microwave background (CMBR). We explore the limits placed on the SFS model parameters by these current data and discuss the viability of the SFS model in question as an alternative to the standard concordance cosmology.

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Future state of the universe

Cited by 20 publications

References 67 publications

Analytically periodic solutions to the three-dimensional Euler–Poisson equations of gaseous stars with a negative cosmological constant

Analytically periodic solutions to the three-dimensional Euler–Poisson equations of gaseous stars with a negative cosmological constant

Singularities and Quantum Gravity

Constraining sudden future singularity models

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