Experimental Tests Of General Relativity Research Articles

A quantum view of photon gravity: The gravitational mass of photon and its implications on previous experimental tests of general relativity

General relativity (GR) is an important theory that requires very stringent tests. So far, its supporting evidence comes mainly from measurements of photon gravitational effects, including light bending near the Sun, gravitational lensing in some galaxies and gravitational redshift of light. These previous experiments were designed based on a hidden assumption, namely, the gravitational mass of a photon is zero; thus, light should not be bent in a gravitational field if there is no space-time curving. In this work, we showed that the gravitational mass of a photon is not zero. Instead, it is equal to its quantum mass, which can be determined from its momentum using the de Broglie relation. Based on this understanding, the gravitational effects of light can be explained more simply using quantum physics. Our findings suggest that, in order to fully evaluate the theory of GR, more stringent experimental tests are required. Some examples of future experiments for testing the principle of equivalence are proposed here.

Is gravity actually the curvature of spacetime?

The Einstein equations, apart from being the classical field equations of General Relativity, are also the classical field equations of two other theories of gravity. As the experimental tests of General Relativity are done using the Einstein equations, we do not really know if gravity is the curvature of a torsionless spacetime or torsion of a curvatureless spacetime or if it occurs due to the nonmetricity of a curvatureless and torsionless spacetime. However, as the classical actions of all these theories differ from each other by the boundary terms, and the Casimir effect is a boundary effect, we propose that a novel gravitational Casimir effect between superconductors can be used to test which of these theories actually describe gravity.

A hundred years of the first experimental test of general relativity

Einsteins general theory of relativity is one of the most important accomplishments in the history of science. Its experimental verification a century ago is therefore an essential milestone that is worth celebrating in full. We reassess the importance of one of the two expeditions that made these measurements possible, a story that involves a sense of adventure and scientific ingenuity in equal measure.

Cosmological self-tuning and local solutions in generalized Horndeski theories

We study both the cosmological self-tuning and the local predictions (inside the Solar system) of the most general shift-symmetric beyond Horndeski theory. We first show that the cosmological self-tuning is generic in this class of theories: By adjusting a mass parameter entering the action, a large bare cosmological constant can be effectively reduced to a small observed one. Requiring then that the metric should be close enough to the Schwarzschild solution in the Solar system, to pass the experimental tests of general relativity, and taking into account the renormalization of Newton's constant, we select a subclass of models which presents all desired properties: It is able to screen a big vacuum energy density, while predicting an exact Schwarzschild-de Sitter solution around a static and spherically symmetric source. As a by-product of our study, we identify a general subclass of beyond Horndeski theory for which regular self-tuning black hole solutions exist, in presence of a time-dependent scalar field. We discuss possible future development of the present work.

Torsion or not torsion, that is the question

A hypothesis of general relativity (GR) is that spacetime torsion vanishes identically. This assumption has no empirical support; in fact, a nonvanishing torsion is compatible with all the experimental tests of GR. The first part of this essay specifies the framework that is suitable to test the vanishing-torsion hypothesis, and an interesting relation with the gravitational degrees of freedom is suggested. In the second part, some original empirical tests are proposed based on the observation that torsion induces new interactions between different spin-polarized particles.

Experimental Test of General Relativity and the Physical Metric

The author will show that neither the Schwarzschild metric nor the metric introduced in 1916 by Schwarzschild describes the data produced by the time delay experiment by Shapiro et al. The author will describe the physical metric that will explain the time delay experiment data correctly as a solution to Einstein Equation of General Relativity. Other tests of General Relativity, the bending of light, the advancement of perihelia, gravitational red shift and gravitational lensing are satisfied by both the Schwarzschild metric and author’s physical metric.

The Physical Metric and Compact Objects

In the previous work, the author introduces the physical metric for spherically symmetric and static metric which satisfies all the experimental tests of general relativity. This metric changes the nature of gravity for compact objects, such as black holes and neutron stars. It introduces the extended horizon which is 2.60 times of the Schwarzschild radius and plays a determinant role in the size of compact objects. This provides the prediction that the gravitational red shift z on the surface of compact objects is universal value of . None of the observed neutron stars rotate fast enough to change this prediction significantly. The gravity inside the extended horizon is repulsive. The effect of this repulsive force causes supernova explosion, high energy cosmic ray generation from AGN and explains the acceleration of the universe expansion.

The Confrontation between General Relativity and Experiment.

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed and updated. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of local Lorentz invariance and clock experiments. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, the Nordtvedt effect in lunar motion, and frame-dragging. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and a growing family of other binary pulsar systems is yielding new tests, especially of strong-field effects. Current and future tests of relativity will center on strong gravity and gravitational waves.

Testing the weak equivalence principle with macroscopic proof masses on ground and in space: A brief review

General relativity is founded on the experimental fact that in a gravitational field all bodies fall with the same acceleration regardless of their mass and composition. This is the weak equivalence principle, or universality of free fall. Experimental evidence of a violation would require either that general relativity is to be amended or that another force of nature is at play. In 1916 Einstein brought as evidence the torsion balance experiments by Eötvös, to 10-8–10-9. In the 1960s and early 70s, by exploiting the "passive" daily rotation of the Earth, torsion balance tests improved to 10-11 and 10-12. More recently, active rotation of the balance at higher frequencies has reached 10-13. No other experimental tests of general relativity are both so crucial for the theory and so precise and accurate. If a similar differential experiment is performed inside a spacecraft passively stabilized by 1 Hz rotation while orbiting the Earth at ≃ 600 km altitude the test would improve by 4 orders of magnitude, to 10-17, thus probing a totally unexplored field of physics. This is unique to weakly coupled concentric macroscopic test cylinders inside a rapidly rotating spacecraft.

Celestial ephemerides in an expanding universe

Post-Newtonian theory was instrumental in conducting the critical experimental tests of general relativity and in building the astronomical ephemerides of celestial bodies in the solar system with an unparalleled precision. The cornerstone of the theory is the postulate that the solar system is gravitationally isolated from the rest of the universe and the background spacetime is asymptotically flat. The present article extends this theoretical concept and formulates the principles of celestial dynamics of particles and light moving in gravitational field of a localized astronomical system embedded to the expanding Friedmann-Lemaitre-Robertson-Walker (FLRW) universe. We formulate the precise mathematical concept of the Newtonian limit of Einstein's field equations in the conformally-flat FLRW spacetime and analyze the geodesic motion of massive particles and light in this limit. We prove that by doing conformal spacetime transformations, one can reduce the equations of motion of particles and light to the classical form of the Newtonian theory. However, the time arguments in the equations of motion of particles and light differ from each other in terms being proportional to the Hubble constant, H. This leads to the important conclusion that the equations of light propagation used currently by Space Navigation Centers for fitting range and Doppler-tracking observations of celestial bodies are missing some terms of the cosmological origin that are proportional to the Hubble constant, H. We also prove that the Hubble expansion does not affect the atomic time scale used in creation of astronomical ephemerides. We derive the cosmological correction to the light travel time equation and argue that their measurement opens an exciting opportunity to determine the local value of the Hubble constant, H, in the solar system independently of cosmological observations.

Resource Letter PTG-1: Precision Tests of Gravity

This Resource Letter provides an introduction to some of the main current topics in experimental tests of general relativity as well as to some of the historical literature. It is intended to serve as a guide to the field for upper-division undergraduate and graduate students, both theoretical and experimental, and for workers in other fields of physics who wish learn about experimental gravity. The topics covered include alternative theories of gravity, tests of the principle of equivalence, solar-system and binary-pulsar tests, searches for new physics in gravitational arenas, and tests of gravity in new regimes, involving astrophysics and gravitational radiation.

Eksperimental'nye proverki obshchei teorii otnositel'nosti: nedavnie uspekhi i budushchie napravleniya issledovanii

Экспериментальные проверки общей теории относительности: недавние успехи и будущие направления исследований, Турышев С.Г.

Experimental Tests of General Relativity

Einstein's general theory of relativity is the standard theory of gravity, especially where the needs of astronomy, astrophysics, cosmology and fundamental physics are concerned. As such, this theory is used for many practical purposes involving spacecraft navigation, geodesy, and time transfer. Here I review the foundations of general relativity, discuss recent progress in the tests of relativistic gravity in the Solar System, and present motivations for the new generation of high-accuracy gravitational experiments. I discuss the advances in our understanding of fundamental physics that are anticipated in the near future and evaluate the discovery potential of the recently proposed gravitational experiments.

The Confrontation between General Relativity and Experiment.

The status of experimental tests of general relativity and of theoretical frameworks for analyzing them is reviewed. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of special relativity, and the gravitational redshift experiment. Ongoing tests of EEP and of the inverse square law are searching for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light deflection, the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational wave damping has been detected in an amount that agrees with general relativity to better than half a percent using the Hulse-Taylor binary pulsar, and other binary pulsar systems have yielded other tests, especially of strong-field effects. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.

A Possible Modification of Einstein's Theory of General Relativity

This article suggests a new metric theory of gravitation, in which metric field is determined not only by matter and nongravitational field but also by vector graviton field, and in principle there is no need to introduce the Einstein's tensor. In order to satisfy automatically the geodesic postulate, an additional coordinate condition is needed. For the spherically symmetric static field, it leads us to quite different conclusions from those of Einstein's general relativity in the interior region of the surface of infinite redshift. Accurate to the first order of , it obtains the same results about the four experimental tests of general relativity.

General relativity experiments in space

Space technology has led to increased accuracy in the measurements of the gravitational redshift and the Shapiro time delay, has permitted the first measurements of the Nordtvedt effect and geodetic (or de Sitter) effect to be made, and has further constrained the parameters in the Parameterized Post Newtonian formalism. These important made, and has further constrained the parameters in the Parameterized Post Newtonian formalism. These important experimental tests of the general of relativity would not have been possible without the capability of launching instruments into space, accurately tracking spacecraft with dual frequency transponders, landing spacecraft on Mars, placing retroreflectors on the surface of the moon, and making precise range measurements to those retroreflectors. The reasons why this technology has been essential are examined. In light of this experience, a number of planned and proposed experimental tests of general relativity are discussed. Increased accuracy in measurements of the geodetic effect and tests of the weak equivalence principle, the first measurements of the Lense-Thrrring effect, and detection of gravitational radiation in space are expected in the next decade.

Testing the Relativistic Effect of the Propagation of Gravity by Very Long Baseline Interferometry

It is shown that the finite speed of gravity affects very-long baseline interferometric observations of quasars during the time of their line-of-sight close angular encounter with Jupiter. The next such event will take place in 2002, September 8. The present Letter suggests a new experimental test of general relativity in which the effect of propagation of gravity can be directly measured by very-long baseline interferometry as an excess time delay in addition to the logarithmic Shapiro time delay (Shapiro, I. I., 1964, Phys. Rev. Lett., 13, 789).

The Confrontation between General Relativity and Experiment

The status of experimental tests of general relativity and of theoretical frameworks for analysing them are reviewed. Einstein’s equivalence principle (EEP) is well supported by experiments such as the Eötvös experiment, tests of special relativity, and the gravitational redshift experiment. Future tests of EEP and of the inverse square law will search for new interactions arising from unification or quantum gravity. Tests of general relativity at the post-Newtonian level have reached high precision, including the light defl ection the Shapiro time delay, the perihelion advance of Mercury, and the Nordtvedt effect in lunar motion. Gravitational wave damping has been detected in an amount that agrees with general relativity to half a percent using the Hulse-Taylor binary pulsar, and new binary pulsar systems may yield further improvements. When direct observation of gravitational radiation from astrophysical sources begins, new tests of general relativity will be possible.

A simple derivation of the Schwarzschild solution from the field equations

A simple method is presented for deriving the Schwarzschild metric in the weak-field limit of the field equations of general relativity. The solution is derived in spherical coordinates natural to the problem, but to which standard weak-field theory does not apply. It is shown that the partial differential equations encountered in the exact analysis decouple, thus eliminating much of the computational labour. The derivation can be used in an undergraduate presentation, where this metric is frequently used to desrcibe the key experimental tests of general relativity, all of which require first-order results.Rezyume. Predlagaetsya prostoi metod vyvoda metriki Schwarzchilda v predele slabykh polei teorii otnositel'nosti. Reshenie predstavlyaetsya v sfericheskikh koordinatakh, estestvennykh dlya problemy, dlya kotorykh standartnaya teoriya slabykh polei neprimenima. Pokazano, chto chastnye differentsial'nye uravneniya, vstrechayushchiesya v tochnom analize, rassoedinyayutsya, isklyuchaya gromozdkie vychisleniya. Etot vyvod mozhet byt' ispol'zovan dlya obucheniya studentov, gde nastoyashchaya metrika chasto ispol'zuetsya dlya opisaniya klyuchevykh eksperimental'nykh proverok teorii otnositel'nosti, trebuyushchikh resul'tatov pervogo poryadka.

Infrared Regularization in Quantum Gravity

Infrared regularization of Feynman amplitudes in perturbative quantum gravity is discussed. Two familiar strategies, momentum cutoff and massification, are critically reviewed. Both methods rely on cancellations (in cross sections) between infrared divergences in individual Feynman diagrams on the one hand, and the contributions of soft gravitons on the other. Cutoffs at the low end of momentum integration have been widely accepted in the context of quantum gravity, though long abandoned in QED; this method is highly ambiguous. The paper is therefore mostly concerned with the alternative strategy of introducing a regulating graviton mass. Difficulties of several kinds arise. Conflicts with the experimental tests of general relativity have been known for a long time, but this is not an absolute deterrent since the experimental uncertainties are considerable. More serious are internal inconsistencies that are reported here, we believe, for the first time. We insist that the massified theory must be internally consistent and find that this modest requirement leads to conflict with the equivalence principle. Earlier work has shown that all mass singularities can be eliminated from the free theory by a change of variables (in the mass theory); the massless limit necessarily involves five degrees of freedom and massless linearized gravity is accompanied by a vector field and a scalar field, so that it has five degrees of freedom. The calculations have been completed to first order in the Newtonian coupling constant only, but this is enough to get us into a difficulty with the equivalence principle, and this in turn suggests that the theory is inconsistent in the next higher order. There are strong indications that additional fields are needed, most likely an antisymmetric tensor field that could be identified with the antisymmetric part of the vierbein.