Address of the President Sir Andrew Huxley, O.M. at the Anniversary Meeting, 30 November 1984

1985 ◽  
Vol 397 (1813) ◽  
pp. 183-196
Keyword(s):  
Stellar Dynamics ◽  
Stellar Structure ◽  
Relativity Theory ◽  
Theoretical Physics ◽  
Structure Theory ◽  
Field Equations ◽  
Subsequent Work ◽  
Dwarf Stars ◽  
The Stability ◽  
Chandrasekhar Limit

The Copley Medal is awarded to Professor Subrahmanyan Chandrasekhar, F. R. S., in recognition of his distinguished work in theoretical physics, including stellar structure, theory of radiation, hydrodynamic stability and relativity. Professor Chandrasekhar has been a major figure in astrophysical sciences since the 1930s. His earliest work, on dwarf stars, led to the concept of the Chandrasekhar limit of stability, which later proved to be a central concept in the origin of the natural elements. He subsequently worked on stellar dynamics and the processes of energy transfer through gaseous bodies. The latter work was followed by a detailed and intensive study of convection in buoyant, rotating and conducting systems which has been fundamental to subsequent work in the field. He also studied the stability of rotating fluid masses. His latest work concerns general relativity theory and solutions of the Einstein field equations, in particular singularities and black holes, where he has shown the importance of these solutions and elucidated their mathematical properties.

Address of the President Sir Andrew Huxley, O. M. at the Anniversary Meeting, 30 November 1984

1985 ◽  
Vol 223 (1233) ◽  
pp. 403-416 ◽  
Keyword(s):  
Stellar Dynamics ◽  
Stellar Structure ◽  
Relativity Theory ◽  
Theoretical Physics ◽  
Structure Theory ◽  
Field Equations ◽  
Subsequent Work ◽  
Dwarf Stars ◽  
The Stability ◽  
Chandrasekhar Limit

The Copley Medal is awarded to Professor Subrahmanyan Chandrasekhar, F. R. S., in recognition of his distinguished work in theoretical physics, including stellar structure, theory of radiation, hydrodynamic stability and relativity. Professor Chandrasekhar has been a major figure in astrophysical sciences since the 1930s. His earliest work, on dwarf stars, led to the concept of the Chandrasekhar limit of stability, which later proved to be a central concept in the origin of the natural elements. He subsequently worked on stellar dynamics and the processes of energy transfer through gaseous bodies. The latter work was followed by a detailed and intensive study of convection in buoyant, rotating and conducting systems which has been fundamental to subsequent work in the field. He also studied the stability of rotating fluid masses. His latest work concerns general relativity theory and solutions of the Einstein field equations, in particular singularities and black holes, where he has shown the importance of these solutions and elucidated their mathematical properties.

Phase space correspondence between Jordan and Einstein frames

2021 ◽  
pp. 2150087
Author(s):  
Amin Salehi
Keyword(s):  
Phase Space ◽  
Critical Point ◽  
Critical Points ◽  
Dynamical Behavior ◽  
Cosmological Parameters ◽  
Jordan Frame ◽  
Field Equations ◽  
Theories Of Gravity ◽  
The Stability ◽  
Jordan And Einstein Frames

Scalar–tensor theories of gravity can be formulated in the Einstein frame or in the Jordan frame (JF) which are related with each other by conformal transformations. Although the two frames describe the same physics and are equivalent, the stability of the field equations in the two frames is not the same. Here, we implement dynamical system and phase space approach as a robustness tool to investigate this issue. We concentrate on the Brans–Dicke theory in a Friedmann–Lemaitre–Robertson–Walker universe, but the results can easily be generalized. Our analysis shows that while there is a one-to-one correspondence between critical points in two frames and each critical point in one frame is mapped to its corresponds in another frame, however, stability of a critical point in one frame does not guarantee the stability in another frame. Hence, an unstable point in one frame may be mapped to a stable point in another frame. All trajectories between two critical points in phase space in one frame are different from their corresponding in other ones. This indicates that the dynamical behavior of variables and cosmological parameters is different in two frames. Hence, for those features of the study, which focus on observational measurements, we must use the JF where experimental data have their usual interpretation.

Impact of f(R,T) gravity in evolution of charged viscous fluids

2021 ◽  
Vol 30 (04) ◽  
pp. 2150027
Author(s):  
I. Noureen ◽  
Usman-ul-Haq ◽  
S. A. Mardan
Keyword(s):  
Stability Analysis ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Viscous Fluids ◽  
Fluid Distribution ◽  
Perturbation Scheme ◽  
Field Equations ◽  
Dynamical Equations ◽  
Stability Of Stars ◽  
The Stability

In this work, the evolution of spherically symmetric charged anisotropic viscous fluids is discussed in framework of [Formula: see text] gravity. In order to conduct the analysis, modified Einstein Maxwell field equations are constructed. Nonzero divergence of modified energy momentum tensor is taken that implicates dynamical equations. The perturbation scheme is applied to dynamical equations for stability analysis. The stability analysis is carried out in Newtonian and post-Newtonian limits. It is observed that charge, fluid distribution, electromagnetic field, viscosity and mass of the celestial objects greatly affect the collapsing process as well as stability of stars.

Relativity Made Relatively Easy Volume 2

2021 ◽  
Author(s):  
Andrew M. Steane
Keyword(s):  
General Relativity ◽  
Classical Field Theory ◽  
Weak Field ◽  
Stellar Structure ◽  
Field Equations ◽  
Graduate Course ◽  
Entry Level ◽  
Introductory Course ◽  
Penrose Process ◽  
Low Amplitude

This is a textbook on general relativity and cosmology for a physics undergraduate or an entry-level graduate course. General relativity is the main subject; cosmology is also discussed in considerable detail (enough for a complete introductory course). Part 1 introduces concepts and deals with weak-field applications such as gravitation around ordinary stars, gravimagnetic effects and low-amplitude gravitational waves. The theory is derived in detail and the physical meaning explained. Sources, energy and detection of gravitational radiation are discussed. Part 2 develops the mathematics of differential geometry, along with physical applications, and discusses the exact treatment of curvature and the field equations. The electromagnetic field and fluid flow are treated, as well as geodesics, redshift, and so on. Part 3 then shows how the field equation is solved in standard cases such as Schwarzschild-Droste, Reissner-Nordstrom, Kerr, and internal stellar structure. Orbits and related phenomena are obtained. Black holes are described in detail, including horizons, wormholes, Penrose process and Hawking radiation. Part 4 covers cosmology, first in terms of metric, then dynamics, structure formation and observational methods. The meaning of cosmic expansion is explained at length. Recombination and last scattering are calculated, and the quantitative analysis of the CMB is sketched. Inflation is introduced briefly but quantitatively. Part 5 is a brief introduction to classical field theory, including spinors and the Dirac equation, proceeding as far as the Einstein-Hilbert action. Throughout the book the emphasis is on making the mathematics as clear as possible, and keeping in touch with physical observations.

scholarly journals On the stability of Einstein universe in f(R, T, Rμν Tμν) gravity

2018 ◽  
Vol 33 (36) ◽  
pp. 1850216 ◽  
Author(s):  
M. Sharif ◽  
Arfa Waseem
Keyword(s):  
State Parameter ◽  
Big Bang ◽  
Graphical Analysis ◽  
Momentum Tensor ◽  
Field Equations ◽  
Einstein Universe ◽  
Existence And Stability ◽  
The Stability ◽  
The Big Bang ◽  
Big Bang Singularity

This paper investigates the existence and stability of Einstein universe in the context of f(R, T, Q) gravity, where Q = R[Formula: see text] T[Formula: see text]. Considering linear homogeneous perturbations around scale factor and energy density, we formulate static as well as perturbed field equations. We parametrize the stability regions corresponding to conserved as well as non-conserved energy–momentum tensor using linear equation of state parameter for particular models of this gravity. The graphical analysis concludes that for a suitable choice of parameters, stable regions of the Einstein universe are obtained which indicates that the big bang singularity can be avoided successfully by the emergent mechanism in non-minimal matter-curvature coupled gravity.

scholarly journals MATHEMATICAL MODELS IN THEORETICAL PHYSICS

Metaphysics ◽  
2020 ◽  
pp. 64-68
Author(s):  
M. L Fil’chenkov ◽  
Yu. P Laptev
Keyword(s):  
Quantum Theory ◽  
Mathematical Models ◽  
Relativity Theory ◽  
Theoretical Physics

Quantum theory and relativity theory as well as possible reconciliation have been analyzed from the viewpoint of mathematical models being used in them, experimental affirmation, interpretations and their association with dualistic paradigms.

scholarly journals NEGOSIASI HETERONORMATIVITAS PADA PERFORMATIVITAS TRANSGENDER DALAM FILM LOVELY MAN

2019 ◽  
Vol 19 (1) ◽  
Author(s):  
Nadya Afdholy
Keyword(s):  
Data Collection ◽  
Narrative Analysis ◽  
Qualitative Method ◽  
Narrative Structure ◽  
Judith Butler ◽  
Structure Theory ◽  
Literature Study ◽  
Using Data ◽  
The Stability ◽  
Tzvetan Todorov

This study aims to reveal heteronormativity in the Lovely Man movie by director Teddy Soeriaatmadja by using narrative structure theory from Tzvetan Todorov and the concept initiated by Judith Butler. Heteronormative values that appear in the film directed by Teddy Soeriaatmadja are seen through dialogue between characters in each scene that are divided into three; (1) equilibrium/plenitude, (2) disruption, disequilibrium/disrupting force, and (3) opposing force. This research uses qualitative method by using approach of narrative analysis of model Tzvetan Todorov. The data used for this research is the film of Lovely Man by director Teddy Soeriaatmadja itself. This study uses data collection techniques with observation and literature study, as well as using data collection techniques with data reduction, interpretation, and conclusions. The results of this study indicate that there is a concept of heteronormative values reflected through heterosexuals who are considered to damage the stability of transvestite life, so that heterosexuals are considered as 'the other' heteronormative. Keywords: Film, Lovely Man, Heteronormativity, Other.

scholarly journals Dynamics of f(R) gravity models and asymmetry of time

2018 ◽  
Vol 27 (02) ◽  
pp. 1850002 ◽  
Author(s):  
Murli Manohar Verma ◽  
Bal Krishna Yadav
Keyword(s):  
Fixed Points ◽  
Quadratic Forms ◽  
Scale Factor ◽  
Gravity Models ◽  
Field Equations ◽  
Classical Level ◽  
The Matrix ◽  
The Stability ◽  
Effects Of Radiation ◽  
Linear And Quadratic Forms

We solve the field equations of modified gravity for [Formula: see text] model in metric formalism. Further, we obtain the fixed points of the dynamical system in phase-space analysis of [Formula: see text] models, both with and without the effects of radiation. The stability of these points is studied against the perturbations in a smooth spatial background by applying the conditions on the eigenvalues of the matrix obtained in the linearized first-order differential equations. Following this, these fixed points are used for analyzing the dynamics of the system during the radiation, matter and acceleration-dominated phases of the universe. Certain linear and quadratic forms of [Formula: see text] are determined from the geometrical and physical considerations and the behavior of the scale factor is found for those forms. Further, we also determine the Hubble parameter [Formula: see text], the Ricci scalar [Formula: see text] and the scale factor [Formula: see text] for these cosmic phases. We show the emergence of an asymmetry of time from the dynamics of the scalar field exclusively owing to the [Formula: see text] gravity in the Einstein frame that may lead to an arrow of time at a classical level.

Randomness in modified general relativity theory: The stochastic f(R) gravity model

2018 ◽  
Vol 96 (11) ◽  
pp. 1173-1177
Author(s):  
Tomer Shushi
Keyword(s):  
Gravity Field ◽  
Gravity Model ◽  
Gravity Models ◽  
Relativity Theory ◽  
Field Equations ◽  
Important Special Case ◽  
Proposed Model ◽  
Stochastic Space ◽  
Wavefunction Collapse ◽  
New Interpretation

We consider a stochastic modification of the f(R) gravity models, and provide its important properties, including the gravity field equations for the model. We show a prediction in which particles are localized by a system of random gravitational potentials. As an important special case, we investigate a gravity model in the presence of a small stochastic space–time perturbation and provide its gravity field equations. Using the proposed model we examine the stochastic quantum mechanics interpretation, and obtain a novel Schrödinger equation with gravitational potential that is based on diffusion in a gravitational field. Furthermore, we provide a new interpretation to the wavefunction collapse. It seems that the stochastic f(R) gravity model causes decoherence of the spatial superposition state of particles.

Langevin's influence on relativity theories

2020 ◽  
Vol 33 (4) ◽  
pp. 380-386
Author(s):  
Douglas A. Staley
Keyword(s):  
Thought Experiment ◽  
Relativity Theory ◽  
Theoretical Physics ◽  
Theory Of Relativity ◽  
Speed Test ◽  
Starting Position ◽  
The Past ◽  
Eclipse Observations ◽  
Stop Watch ◽  
Light Beams

A century ago, Paul Langevin [C. R. 173, 831 (1921)], through his influence, convinced the scientific community that Einstein's theories of relativity were correct and could explain the Sagnac effect. A simple note in Comptes Rendus was all it took to silence many prominent skeptical scientists. The relativity skeptics had pointed to Sagnac's experiment [C. R. 157, 1410 (1913)] with the interference of counter rotating light beams as proof that the speed of light was not the same in both directions, contrary to the key postulate in Einstein's theory. Langevin showed that the result was also explained by relativity. The rest is history, and relativity has remained a center piece of theoretical physics ever since. Langevin had been captivated by solar eclipse observations of a shifted star pattern near the sun as reported by Eddington [Report on the Relativity Theory of Gravitation (Fleetway Press, Ltd., London, 1920)]. This was taken as proof positive for Einstein's General Theory of Relativity. The case of a light beam split into two beams, which propagate in opposite directions around a circuit, has an analog in a simple thought experiment—a speed test for runners. Two runners can be timed on a running track with the runners going around the track in opposite directions. Two stop watches will display the time for each runner's return to the starting position. The arithmetic difference in time shown on each stop watch will provide the differences in speed between the two runners. If the two speeds are the same, the time difference will be zero. It would not make any sense for one of the stop watches to measure a negative time, that is, time moving into the past. In fact, the idea is absurd! However, Langevin did just that, assigned the time for light to travel in one direction as positive while the time for the light to traverse in the opposite direction as negative, moving into the past! By so doing, Langevin reproduced Sagnac's expression and declared that relativity explains Sagnac's experiment. Langevin was wrong!

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