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Register a new userAbolishing the maximum tension principle
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Added by
Mariusz Dabrowski P.
Publication date
2015
fields
Physics
and research's language is
English
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We find the series of example theories for which the relativistic limit of maximum tension $F_{max} = c^4/4G$ represented by the entropic force can be abolished. Among them the varying constants theories, some generalized entropy models applied both for cosmological and black hole horizons as well as some generalized uncertainty principle models.
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Three simple idealised models are studied in order to develop some intuition about the leading order effect of non-sphericity on the maximum turnaround size $R_{rm TA,max}$ of large scale bound cosmic structures. Two of them describe intrinsically axisymmetric static mass distributions whereas the other is the Kerr-de Sitter metric where the axisymmetry is generated due to the rotation of the structure. In all the cases the fractional change $delta R_{rm TA,max}(theta)/R^{(0)}_{rm TA,max}$ of $R_{rm TA,max}$ of a given structure, compared to a spherical one with the same mass $M$, depends on the polar angle $theta$ and is proportional to the product of the relevant eccentricity parameter, times the square of a small quantity. This quantity in the static examples is the ratio of two characteristic length scales, while in the spinning case it is the ratio $v_{rm out}/c$ of the azimuthal speed of the outmost members of the structure, over the speed of light. Furthermore, the angular average $langle delta R_{rm TA,max}(theta)/R^{(0)}_{rm TA,max}rangle$ is zero in the two static cases, while it is negative and proportional to ${cal O}(v^2_{rm out}/c^2)$ for the Kerr-de Sitter. Thus, $delta R_{rm TA,max}(theta)/R^{(0)}_{rm TA,max}$ for an axisymmetric structure is very small for practically any value of the eccentricity parameter. We speculate about some possible further implications of our result on the maximum turn around radius of realistic cosmic structures.
Although the idea that there is a maximum force in nature seems untenable, we explore whether this concept can make sense in the restricted context of black holes. We discuss uniformly accelerated and cosmological black holes and we find that, although a maximum force acting on these black holes can in principle be introduced, this concept is rather tautological.
Einstein equivalence principle (EEP), as one of the foundations of general relativity, is a fundamental test of gravity theories. In this paper, we propose a new method to test the EEP of electromagnetic interactions through observations of black hole photon rings, which naturally extends the scale of Newtonian and post-Newtoian gravity where the EEP violation through a variable fine structure constant has been well constrained to that of stronger gravity. We start from a general form of Lagrangian that violates EEP, where a specific EEP violation model could be regarded as one of the cases of this Lagrangian. Within the geometrical optical approximation, we find that the dispersion relation of photons is modified: for photons moving in circular orbit, the dispersion relation simplifies, and behaves such that photons with different linear polarizations perceive different gravitational potentials. This makes the size of black hole photon ring depend on polarization. Further assuming that the EEP violation is small, we derive an approximate analytic expression for spherical black holes showing that the change in size of the photon ring is proportional to the violation parameters. We also discuss several cases of this analytic expression for specific models. Finally, we explore the effects of black hole rotation and derive a modified proportionality relation between the change in size of photon ring and the violation parameters. The numerical and analytic results show that the influence of black hole rotation on the constraints of EEP violation is relatively weak for small magnitude of EEP violation and small rotation speed of black holes.
In this paper we give a physical explanation to the accelerated expansion of the Universe, alleviating the tension between the discrepancy of Hubble constant measurements. By the Euler Cauchy stress principle, we identify a controversy on the lack of consideration of the surface forces contemplated in the study of the expansion of the Universe. We distinguish a new effect that modifies the spacetime fabric by means of the energy conservation equation. The resulting dynamical equations from the proposed hypothesis are contrasted to several testable astrophysical predictions. This paper also explains why we have not found any particle or fluid responsible for dark energy and clarifies the Cosmological Coincidence Problem. These explanations are achieved without assuming the existence of exotic matter of unphysical meaning or having to modify the Einsteins Field Equations.
The Hubble tension is shown to be solvable, without any free parameter, conceptually and quantitatively, within the approach of modified weak-field General Relativity involving the cosmological constant $Lambda$. That approach enables one to describe in a unified picture both the dynamics of dark matter containing galaxies and the accelerated expansion of the Universe, thus defining a {it local} Hubble constant of a local flow and the {it global} one. The data on the dark matter content of peculiar galaxy samples are shown to be compatible to that unified picture. Future more refined surveys of galaxy distribution, hierarchical dynamics and flows within the vicinity of the Local group and the Virgo supercluster can be decisive in revealing the possible common nature of the dark sector.
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