Physics: Relativity And Gravitation

In this essay, the author

• Describes the key pillars of theoretical physics and its enormous success.
• Opines that gr is a highly successful theory which has not only radically modified the theory, but has also changed the world.
• Opines that while there is little doubt that gr embodies the spirit of gravitational physics in the summary.
• Explains that even cosmology suggests that gravity may not be described exactly by gr.
• Describes the complicated issues arising from gr, including the lack of a consistent explanation of the problem.
• Opines that the existence of the spiral arms of galaxies has placed considerable doubts on the validity of not only the theory.
• Opines that as the list of inconsistencies in einstein’s theory of gravitation increases, more and more physicists are interested.
• Analyzes how the general framework presented in modified theories of gravity has increased with each year.
• Explains that binary pulsars can be used as probes for some aspects of the strong-gravity regime of gr.
• Explains the times-of-emission of pulses, to their times of arrival on earth for a large class of metric theories.
• Explains that the dynamical but quasi-linear regime can be used to verify the motion of compact objects.
• Explains that the strong-field probes non-linear stellar-structural eects and are ineective.
• Opines that blackhole accretion discs, may probe gr in the non-linear regime in verification.
• Explains that only gravitational waves are capable of testing gr in the strong-field fully non-linear.
• Describes possible deviations from gr that may be as large as 10 orders of magnitude more stringent.
• Explains that tests of the theory within the solar system places a bound of! 40000, which implies that all its
• Explains how gravity into special relativity (sr) was successfully tested in the solar system and confirmed the predictions of the gravitational bending of sr.
• Explains how the theory gained credibility when it correctly explained the anomalous precession of the perihelion of mercury’s orbit.
• Explains that tools were used to detect radiowaves from sources under the gravitational influence of the sun up to a few parts of 104.
• Explains that the theory has passed with extraordinary precision, all the experimental and observational tests that it has been subjected to.
• Explains that weak-field tests only probe the post-newtonian range of the theory, implying that relativistic eects are still important in this regime.
• Explains that such terms significantly altered the theory leaving its field equations at fourth order rather than second.
• Explains that even string theory at the low-energy limit fails to reproduce gr but instead produces a scalar-tensor theory of gravity.
• Explains how a mysterious new field known as dark energy is introduced to explain the cosmic acceleration within the context of gr. its eects can best be described as anti-gravitation.
• Explains that spacetime around a blackhole is easier to describe than the physical nature of the actual black hole.
• Explains that evolution of a uniform and isotropic universe backward in time, results in the big bang.
• Explains that curiosity is unphysical in the classical sense although these pathologies are heuristic or physical.
• Explains that cosmologists have been forced to invoke yet another exotic and undetectable type of matter to explain galaxy dynamics.
• Opines that tests of the theory in the dynamical strong-field regime have not been available.
• Explains why direct strong-gravity measurements remain seemingly unattainable, citing the absence of an agreed consensus on the nature of the universe.
• Describes hulse and taylor's discovery of the binary pulsar psr b1913+16 in the constellation aquila (the eagle) in 1975.
• Explains that binary systems tend to have orbital periods of a few hours, including lightcrossing times, so that their orbitals velocities are of the order of
• Explains that velocity is much less than the speed of light where v=c 1. the parametrized post-keplerian (ppk) formalism was constructed in 1992.
• Explains that the strong gravitational field of relativistic compact objects such as blackholes, neutron stars or the early universe is subject to astrophysical observations.
• Explains that binary pulsars initially played a key role as the initiators of indirect detection of gravitational waves. this later helped eliminate alternate theories such as rosen's bimetric gravity.
• Explains that a binary system consisting of neutron stars and/or blackholes may merge, implying that direct gravitational wave detection is possible.
• Explains that scalar-tensor theories of gravity (stt) are the most well-tested contenders to gr. they were first proposed in 1969 by brans and dicke (bd).
• Opines that to construct an stt whose strong-field predictions deviate signicantly from gr while passing the stringent solar-system tests, it is necessary to generalize the bd theory by replacing the parameter!
• Explains that they constructed a two-parameter family of models t( 0 ; 00) that passes solar system tests while predicting deviations from gr in the strongfield regime.
• Explains that def constructed a quadratic extension of bd theory in 1993 to investigate stellar structure with one scalar field whose coupling to matter is determined by the
• Explains that gr in the strong-field regime were induced by an interaction between matter and scalar fields via the conformal factor a().
• Explains that spontaneous scalarization occurs in ferromagnets at low temperatures below the critical curie limit in gravitational physics.