scholarly journals Gravitational Lensing and Modified Newtonian Dynamics

2001 ◽  
Vol 18 (2) ◽  
pp. 189-191
Author(s):  
Daniel J. Mortlock ◽  
Edwin L. Turner
Keyword(s):  
General Relativity ◽  
Gravitational Lensing ◽  
A Priori ◽  
Massive Particle ◽  
Speed Of Light ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Visible Matter ◽  
Relativistic Extension ◽  
The Universe

AbstractGravitational lensing is most often used as a tool to investigate the distribution of (dark) matter in the universe, but, if the mass distribution is known a priori, it becomes, at least in principle, a powerful probe of gravity itself. Lensing observations are a more powerful tool than dynamical measurements because they allow measurements of the gravitational field far away from visible matter. For example, modified Newtonian dynamics (MOND) has no relativistic extension, and so makes no firm lensing predictions, but galaxy–galaxy lensing data can be used to empirically constrain the deflection law of a MONDian point-mass. The implied MONDian lensing formalism is consistent with general relativity, in so far as the deflection experienced by a photon is twice that experienced by a massive particle moving at the speed of light. With the deflection law in place and no invisible matter, MOND can be tested wherever lensing is observed.

scholarly journals Alternatives to Dark Matter (?)

2004 ◽  
Vol 220 ◽  
pp. 17-26 ◽  
Author(s):  
Anthony Aguirre
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
General Idea ◽  
Galactic Dynamics ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Visible Matter

It has long been known that Newtonian dynamics applied to the visible matter in galaxies and clusters does not correctly describe the dynamics of those systems. While this is generally taken as evidence for dark matter it is in principle possible that instead Newtonian dynamics (and with it General Relativity) breaks down in these systems. Indeed there have been a number of proposals as to how standard gravitational dynamics might be modified so as to correctly explain galactic dynamics without dark matter. I will review this general idea (but focus on “MOdified Newtonian Dynamics”, or “MOND”), and discuss a number of ways alternatives to dark matter can be tested and, in many cases, ruled out.

MOND as the basis for an extended theory of gravity

2015 ◽  
Vol 93 (2) ◽  
pp. 217-231 ◽  
Author(s):  
S. Mendoza
Keyword(s):  
Equivalence Principle ◽  
Clusters Of Galaxies ◽  
Relativistic Theory Of Gravity ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Acceleration Of The Universe ◽  
Theory Of Gravity ◽  
The Universe ◽  
Geometric Nature ◽  
Bending Of Light

This review describes why the geometric nature of space–time, the Einstein equivalence principle, and the geodesic motion of particles show the possibility of building an extended relativistic theory of gravity on regions where the Tully–Fisher law is valid. It is also shown how a metric construction of gravity can have a modified Newtonian dynamics behaviour compatible with the Tully–Fisher law and the bending of light observed in individual, groups, and clusters of galaxies. It is also reviewed how this metric theory of gravity fits reasonably well on cosmological scales explaining the current acceleration of the universe.

scholarly journals How can rainbow gravity affect gravitational force?

2016 ◽  
Vol 25 (14) ◽  
pp. 1650101 ◽  
Author(s):  
Akram Sadat Sefiedgar
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Gravitational Force ◽  
Entropic Force ◽  
Recent Proposal ◽  
Modified Newtonian Dynamics ◽  
Corrected Entropy ◽  
Newtonian Dynamics ◽  
Area Law ◽  
Einstein’S General Relativity

According to Verlinde’s recent proposal, the gravity is originally an entropic force. In this paper, we obtain the corrections to the entropy-area law of black holes within rainbow gravity. The corrected entropy-area law leads to the modifications of the number of bits [Formula: see text]. Inspired by Verlinde’s argument on the entropic force, and using the modified number of bits, we can investigate the effects of rainbow gravity on the modified Newtonian dynamics, Newton’s law of gravitation, and Einstein’s general relativity in entropic force approach.

scholarly journals How to Measure Gravitational Aberration?

2006 ◽  
Vol 2 (S240) ◽  
pp. 670-677
Author(s):  
Michal Křížek ◽  
Alena Šolcová
Keyword(s):  
A Priori ◽  
Hubble Constant ◽  
The Moon ◽  
Speed Of Light ◽  
Henri Poincaré ◽  
The Earth ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Equations With Delay ◽  
Two Bodies

AbstractIn 1905, Henri Poincaré predicted the existence of gravitational waves and assumed their speed equal to the speed of light. If additionally the gravitational aberration would have the same magnitude as the aberration of light, we would observe several paradoxical phenomena. For instance, the orbit of two bodies would be unstable, since two attractive forces arise that are not in line and hence form a couple. This will be modelled by a nonautonomous system of ordinary differential equations with delay. In fact, any positive value of the gravitational aberration increases the angular momentum of such a system and this may contribute to the expansion of the universe. We found a remarkable coincidence between the Hubble constant and the increasing distance of the Moon from the Earth.In 2000, Carlip showed that in general relativity gravitational aberration is almost cancelled out by velocity–dependent interactions. We show how the actual value of the gravitational aberration can be obtained by measurement of a single angle at a suitable time t* corresponding to the perihelion of an elliptic orbit. We also derive an a priori error estimate that expresses how accurately t* has to be determined to obtain the gravitational aberration to a prescribed tolerance.

scholarly journals Gravitational Waves from Compact Bodies

1996 ◽  
Vol 165 ◽  
pp. 153-183
Author(s):  
Kip S. Thorne
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Neutron Stars ◽  
Gravitational Radiation ◽  
Relativity Theory ◽  
Energy Concentration ◽  
Speed Of Light ◽  
General Relativity Theory ◽  
Concentration Changes ◽  
The Universe

According to general relativity theory, compact concentrations of energy (e.g., neutron stars and black holes) should warp spacetime strongly, and whenever such an energy concentration changes shape, it should create a dynamically changing spacetime warpage that propagates out through the Universe at the speed of light. This propagating warpage is called gravitational radiation — a name that arises from general relativity's description of gravity as a consequence of spacetime warpage.

THE HOLOGRAPHIC SCENARIO, THE MODIFIED INERTIA AND THE DYNAMICS OF THE UNIVERSE

2012 ◽  
Vol 27 (34) ◽  
pp. 1250208 ◽  
Author(s):  
JAUME GINÉ
Keyword(s):  
Casimir Effect ◽  
Dynamical Evolution ◽  
High Energy ◽  
Accelerated Expansion ◽  
Late Time ◽  
Holographic Model ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Expansion Of The Universe ◽  
The Universe

This paper attempts to connect two new gravitational mechanisms: the Verlinde's holographic model of gravity and the modification of inertia resulting from a Hubble-scale Casimir effect (MiHsC) of McCulloch. First we give a short survey about how the holographic scenario can give the correct dynamics of the universe. The introduction of a two-holographic screens one comparable to the Hubble horizon and a second screen that takes into account the contribution of all the matter between the test particle and the observer gives directly the modified Friedmann acceleration equation for the dynamical evolution of the universe. Improvements of this equation using the quantum corrections will realize the inflation at high energy scales and the late-time acceleration (i.e. the accelerated expansion of the universe nowadays) obviating the dark energy. From both models we can derive a version of Modified Newtonian Dynamics (MOND) observed in the dynamics of the astronomical objects obviating the dark matter and explaining other astronomical anomalies. A first connection between both theories is given at the end of the paper.

Dark matter (energy) may be indistinguishable from modified gravity (MOND)

2017 ◽  
Vol 26 (12) ◽  
pp. 1743010 ◽  
Author(s):  
C. Sivaram
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Dark Energy ◽  
Modified Gravity ◽  
Observational Evidence ◽  
Negative Results ◽  
Newtonian Dynamics ◽  
Special Cases ◽  
The Universe ◽  
Matter Energy

For Newtonian dynamics to hold over galactic scales, large amounts of dark matter (DM) are required which would dominate cosmic structures. Accounting for the strong observational evidence that the universe is accelerating requires the presence of an unknown dark energy (DE) component constituting about 70% of the matter. Several ingenious ongoing experiments to detect the DM particles have so far led to negative results. Moreover, the comparable proportions of the DM and DE at the present epoch appear unnatural and not predicted by any theory. For these reasons, alternative ideas like MOND and modification of gravity or general relativity over cosmic scales have been proposed. It is shown in this paper that these alternate ideas may not be easily distinguishable from the usual DM or DE hypotheses. Specific examples are given to illustrate this point that the modified theories are special cases of a generalized DM paradigm.

scholarly journals One Observer Universe: A Geometric Interpretation of Speed of Light and Mass

2020 ◽  
Author(s):  
Ahmed Farag Ali
Keyword(s):  
General Relativity ◽  
Special Relativity ◽  
Geometric Interpretation ◽  
Space Time ◽  
Red Shift ◽  
General Covariance ◽  
Speed Of Light ◽  
The Universe

In this paper, we investigate how Rindler observer measures the universe in the ADM formalism. We compute his measurements in each slice of the space-time in terms of gravitational red-shift which is a property of general covariance. In this way, we found special relativity preferred frames to match with the general relativity Rindler frame in ADM formalism. This may resolve the widely known incompatibility between special relativity and general relativity on how each theory sees the red-shift. We found a geometric interpretation of the speed of light and mass.

scholarly journals Tensor–vector–scalar-modified gravity: from small scale to cosmology

2011 ◽  
Vol 369 (1957) ◽  
pp. 5003-5017 ◽  
Author(s):  
Jacob D. Bekenstein
Keyword(s):  
Gravitational Lensing ◽  
Modified Gravity ◽  
Gravity Theory ◽  
Small Scale ◽  
Scalar Theory ◽  
Modified Newtonian Dynamics ◽  
Newtonian Dynamics ◽  
Modified Gravity Theory ◽  
The Face ◽  
Standard Cosmological Model

The impressive success of the standard cosmological model has suggested to many that its ingredients are all that one needs to explain galaxies and their systems. I summarize a number of known problems with this programme. They might signal the failure of standard gravity theory on galaxy scales. The requisite hints as to the alternative gravity theory may lie with the modified Newtonian dynamics (MOND) paradigm, which has proved to be an effective summary of galaxy phenomenology. A simple nonlinear modified gravity theory does justice to MOND at the non-relativistic level, but cannot be consistently promoted to relativistic status. The obstacles were first side-stepped with the formulation of tensor–vector–scalar theory (T e V e  S), a covariant-modified gravity theory. I review its structure, its MOND and Newtonian limits, and its performance in the face of galaxy phenomenology. I also summarize features of T e V e  S cosmology and describe the confrontation with data from strong and weak gravitational lensing.

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