On the distinction between coordinate and physical speed of light in general relativity

2020 ◽  
Vol 31 (5-6) ◽  
pp. 793-802
Author(s):  
Elmo Benedetto ◽  
Fabiano Feleppa ◽  
Biancamaria Sersante
Keyword(s):  
General Relativity ◽  
Speed Of Light

scholarly journals Study of gravitational constant and mercury's precession from perspective of physical aesthetics and ideal fluid

2020 ◽  
Author(s):  
Yun-Gang Li ◽  
Cheng-Shu Li
Keyword(s):  
General Relativity ◽  
Ideal Fluid ◽  
Gravitational Constant ◽  
Speed Of Light ◽  
Research Teams ◽  
Space Agency ◽  
G Value ◽  
The Masses ◽  
New Formula ◽  
Einstein’S General Relativity

Newton's law of universal gravitation does not explain the Mercury's orbit anomalous precession, and the gravitational constant G values measured by different research teams do not coincide. This paper studied the two problems from a physical aesthetics and ideal fluid perspective, and derived a new formula for calculating the exact G value by using the speed of light in vacuum, including formulas for error correction, and verified by experimental results of other scientists. After being corrected, the G values measured by some famous surveyors approximately coincide with a specific value. The formulas also verified by the precession of Mercury's orbit and contribute an additional 35.94"/cy to the theoretical calculation value, the Mercury's anomalous precession, calculated by Le Verrier, is then reduced from 38"/cy to about 2"/cy. This provides another explanation for Mercury's anomalous precession which is completely different from that of Einstein's general relativity. Conclusion is that G equals 1/(16πc) when the masses are mass points and the Mercury's orbit anomalous precession equals 43"/cy should not be the evidence for prove Einstein's general relativity is correct. Further, this paper also presented an experimental plan for the space agency to verify who is right.

scholarly journals Counterexamples to the Maximum Force Conjecture

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 403
Author(s):  
Aden Jowsey ◽  
Matt Visser
Keyword(s):  
General Relativity ◽  
Dimensional Analysis ◽  
Maximum Force ◽  
Explicit Calculation ◽  
General Notion ◽  
Physical Situation ◽  
Speed Of Light ◽  
Maximum Tension ◽  
Dimensionless Function ◽  
Fluid Spheres

Dimensional analysis shows that the speed of light and Newton’s constant of gravitation can be combined to define a quantity F*=c4/GN with the dimensions of force (equivalently, tension). Then in any physical situation we must have Fphysical=fF*, where the quantity f is some dimensionless function of dimensionless parameters. In many physical situations explicit calculation yields f=O(1), and quite often f≤1/4. This has led multiple authors to suggest a (weak or strong) maximum force/maximum tension conjecture. Working within the framework of standard general relativity, we will instead focus on idealized counter-examples to this conjecture, paying particular attention to the extent to which the counter-examples are physically reasonable. The various idealized counter-examples we shall explore strongly suggest that one should not put too much credence into any truly universal maximum force/maximum tension conjecture. Specifically, idealized fluid spheres on the verge of gravitational collapse will generically violate the weak (and strong) maximum force conjectures. If one wishes to retain any truly general notion of “maximum force” then one will have to very carefully specify precisely which forces are to be allowed within the domain of discourse.

scholarly journals Gravitational waves in modified Gauss–Bonnet gravity

2020 ◽  
Vol 29 (10) ◽  
pp. 2050072
Author(s):  
Tomohiro Inagaki ◽  
Masahiko Taniguchi
Keyword(s):  
General Relativity ◽  
Gravitational Waves ◽  
Wave Equations ◽  
Massive Scalar ◽  
Speed Of Light ◽  
Bonnet Gravity ◽  
Cosmological Background ◽  
Background Curvature ◽  
Scalar Mode ◽  
Metric Perturbation

We study the gravitational waves (GWs) in modified Gauss–Bonnet gravity. Applying the metric perturbation around a cosmological background, we obtain explicit expressions for the wave equations. It is shown that the speed of the traceless mode is equal to the speed of light. An additional massive scalar mode appears in the propagation of the GWs. To find phenomena beyond the general relativity, the scalar mode mass is calculated as a function of the background curvature in some typical models.

A derivation of Shape Dynamics

2018 ◽  
Author(s):  
Flavio Mercati
Keyword(s):  
Field Theory ◽  
General Relativity ◽  
Gravitational Field ◽  
The Other ◽  
Speed Of Light ◽  
Symmetry Principle ◽  
Shape Dynamics ◽  
Diffeomorphism Invariance ◽  
The One

By applying the principles of relational field theory to the gravitational field, and using 3D diffeomorphism invariance as our symmetry principle for best matching, it is feasible to reduce the working possibilities to just a few cases. One is a field-theory version of (GR), which is the limit of General Relativity in which the speed of light goes to infinity and the light cones open up to provide a notion of absolute simultaneity. Another is the opposite limit, dubbed ‘Carrollian Relativity’ by Levy–Leblond, in which the speed of light goes to zero and each point is causally isolated from the other. This limit is related to the so-called ‘BKL’ behaviour that appears to be universal near singularities. The penultimate possibility is (GR), while the last one is SD, which emerges as the unique generalization of the theory that allows for an arbitrary value of the one free coefficient in the supermetric.

scholarly journals Gravity between Newton and Einstein

2019 ◽  
Vol 28 (14) ◽  
pp. 1944010 ◽  
Author(s):  
Dennis Hansen ◽  
Jelle Hartong ◽  
Niels A. Obers
Keyword(s):  
General Relativity ◽  
Causal Structure ◽  
Relativistic Effects ◽  
Newtonian Gravity ◽  
Speed Of Light ◽  
Perihelion Precession ◽  
Tests Of General Relativity ◽  
Deflection Of Light ◽  
Weak Fields ◽  
Large Speed

Statements about relativistic effects are often subtle. In this essay we will demonstrate that the three classical tests of general relativity, namely perihelion precession, deflection of light and gravitational redshift, are passed perfectly by an extension of Newtonian gravity that includes gravitational time dilation effects while retaining a non-relativistic causal structure. This non-relativistic gravity theory arises from a covariant large speed of light expansion of Einstein’s theory of gravity that does not assume weak fields and which admits an action principle.

scholarly journals Foundations of Finsler Spacetimes from the Observers’ Viewpoint

Universe ◽  
2020 ◽  
Vol 6 (4) ◽  
pp. 55 ◽  
Author(s):  
Antonio N. Bernal ◽  
Miguel A. Javaloyes ◽  
Miguel Sánchez
Keyword(s):  
General Relativity ◽  
Special Relativity ◽  
Linear Approximation ◽  
Classical Mechanics ◽  
Finsler Metric ◽  
Speed Of Light ◽  
Cone Structure ◽  
Mathematical Definition ◽  
Finsler Spacetime ◽  
Definition Of

Physical foundations for relativistic spacetimes are revisited in order to check at what extent Finsler spacetimes lie in their framework. Arguments based on inertial observers (as in the foundations of special relativity and classical mechanics) are shown to correspond with a double linear approximation in the measurement of space and time. While general relativity appears by dropping the first linearization, Finsler spacetimes appear by dropping the second one. The classical Ehlers–Pirani–Schild approach is carefully discussed and shown to be compatible with the Lorentz–Finsler case. The precise mathematical definition of Finsler spacetime is discussed by using the space of observers. Special care is taken in some issues such as the fact that a Lorentz–Finsler metric would be physically measurable only on the causal directions for a cone structure, the implications for models of spacetimes of some apparently innocuous hypotheses on differentiability, or the possibilities of measurement of a varying speed of light.

scholarly journals Can a negative-mass cosmology explain dark matter and dark energy?

2019 ◽  
Vol 626 ◽  
pp. A5 ◽  
Author(s):  
H. Socas-Navarro
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Model ◽  
Large Scale ◽  
Dark Matter Halos ◽  
Challenging Problem ◽  
Speed Of Light ◽  
Negative Mass ◽  
Galactic Dark Matter

A recent study by Farnes (2018, A&A, 620, A92) proposed an alternative cosmological model in which both dark matter and dark energy are replaced with a single fluid of negative mass. This paper presents a critical review of that model. A number of problems and discrepancies with observations are identified. For instance, the predicted shape and density of galactic dark matter halos are incorrect. Also, halos would need to be less massive than the baryonic component, otherwise they would become gravitationally unstable. Perhaps the most challenging problem in this theory is the presence of a large-scale version of the “runaway effect”, which would result in all galaxies moving in random directions at nearly the speed of light. Other more general issues regarding negative mass in general relativity are discussed, such as the possibility of time-travel paradoxes.

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