Solar System Experiments Research Articles

The speed of gravity — What the experiments say

Laboratory, solar system, and astrophysical experiments for the “speed of gravity” yield a lower limit of 2 × 10 10 c. The link between relativity and the causality principle involves issues of the meaning of gravitational waves and curved space-time analogies. Apparently, Lorentzian relativity better describes nature than special relativity.

Tensor-scalar gravity and binary-pulsar experiments.

Some recently discovered nonperturbative strong-field effects in tensor-scalar theories of gravitation are interpreted as a scalar analog of ferromagnetism: "spontaneous scalarization". This phenomenon leads to very significant deviations from general relativity in conditions involving strong gravitational fields, notably binary-pulsar experiments. Contrary to solar-system experiments, these deviations do not necessarily vanish when the weak-field scalar coupling tends to zero. We compute the scalar "form factors" measuring these deviations, and notably a parameter entering the pulsar timing observable gamma through scalar-field-induced variations of the inertia moment of the pulsar. An exploratory investigation of the confrontation between tensor-scalar theories and binary-pulsar experiments shows that nonperturbative scalar field effects are already very tightly constrained by published data on three binary-pulsar systems. We contrast the probing power of pulsar experiments with that of solar-system ones by plotting the regions they exclude in a generic two-dimensional plane of tensor-scalar theories.

Constraints on the scalar-tensor theories of gravitation from primordial nucleosynthesis.

We present a detailed calculation of the light element production in the framework of Scalar-Tensor (ST) theories of gravitation. The coupling function \omega has been described by an appropriate form which reproduces all the possible asymptotic behaviors at early times of viable ST cosmological models with a monotonic \omega(\Phi). This form gives an exact representation for most of the particular theories proposed in the literature, but also a first-order approximation to many other theories. In most of ST theories, the nucleosynthesis bounds lead to cosmological models which do not significantly differ from the standard FRW ones. We have found however a particular class of ST theories where the expansion rate of the universe during nucleosynthesis can be very different from that found in GR, while the present value of \omega is high enough to ensure compatibility with solar-system experiments. In the framework of this class of theories, right primordial abundances can be obtained for a baryon density range much wider (2.8 \lesssim \eta_{10} \lesssim 58.7) than in GR. Consequently, the usual constraint on the baryon contribution to the density parameter of the universe can be drastically relaxed (0.01 \lesssim \Omega_{b0} \lesssim 1.38) by considering these gravity theories. This is the first time that a ST theory is found to be compatible both with primordial nucleosynthesis and solar-system experiments while implying cosmological models significantly different from the FRW ones.

Scalar-tensor cosmological models.

We analyze the qualitative behavior of scalar-tensor cosmologies with an arbitrary monotonic \ensuremath{\omega}(\ensuremath{\Phi}) function. In particular, we are interested in scalar-tensor theories distinguishable at early epochs from general relativity (GR) but leading to predictions compatible with solar-system experiments. After extending the method developed by Lorentz-Petzold and Barrow, we establish the conditions required for convergence towards GR at t\ensuremath{\rightarrow}\ensuremath{\infty}. Then, we obtain all the asymptotic analytical solutions at early times which are possible in the framework of these theories. The subsequent qualitative evolution, from these asymptotic solutions until their later convergence towards GR, is analyzed by means of numerical computations. From this analysis, we are able to establish a classification of the different qualitative behaviors of scalar-tensor cosmological models with an arbitrary monotonic \ensuremath{\omega}(\ensuremath{\Phi}) function. \textcopyright{} 1996 The American Physical Society.

Testing scalar-tensor gravity with gravitational-wave observations of inspiralling compact binaries.

Observations of gravitational waves from inspiralling compact binaries using laser-interferometric detectors can provide accurate measures of parameters of the source. They can also constrain alternative gravitation theories. We analyse inspiralling compact %binaries in the context of the scalar-tensor theory of Jordan, Fierz, Brans and Dicke, focussing on the effect on the inspiral of energy lost to dipole gravitational radiation, whose source is the gravitational self-binding energy of the inspiralling bodies. Using a matched-filter analysis we obtain a bound on the coupling constant $\omega_{\rm BD}$ of Brans-Dicke theory. For a neutron-star/black-hole binary, we find that the bound could exceed the current bound of $\omega_{\rm BD}>500$ from solar-system experiments, for sufficiently low-mass systems. For a $0.7 M_\odot$ neutron star and a $3 M_\odot$ black hole we find that a bound $\omega_{\rm BD} \approx 2000$ is achievable. The bound decreases with increasing black-hole mass. For binaries consisting of two neutron stars, the bound is less than 500 unless the stars' masses differ by more than about $0.5 M_\odot$. For two black holes, the behavior of the inspiralling binary is observationally indistinguishable from its behavior in general relativity. These bounds assume reasonable neutron-star equations of state and a detector signal-to-noise ratio of 10.

Cosmological models in the Schmidt-Greiner-Heinz-Müller theory of gravitation.

An exhaustive study of homogeneous and isotropic cosmological models in the Schmidt-Greiner-Heinz-M\"uller (SGHM) theory of gravitation is performed, where present values of dynamical functions are consistent with astronomical observations and solar-system experiments. We find two types of SGHM models: a first class which is exactly equal to the standard general relativistic (GR) cosmological models, and a second class which never reduces to GR. Some analytical and numerical solutions for the second type of SGHM models are then obtained. The age of the Universe predicted by these models is compatible with the age of old globular clusters except for weak bounds on the ${\ensuremath{\Delta}}_{0}$ parameter defined in this paper.

A parity-violatingU 4-gravitation theory

The general structure of a metric-torsion theory of gravitation allows a parity-violating contribution to the complete action which is linear in the curvature tensor and vanishes identically in the absence of torsion. The resulting action involves, apart from the constant ¯K E =8pgr/c4, a coupling (B) which governs the strength of the parity interaction mediated by torsion. In this model the Brans-Dicke scalar field generates the torsion field, even though it has zero spin. The interesting consequence of the theory is that its results for the solar-system differ very little from those obtained from Brans-Dicke (BD) theory. Therefore the theory is indistinguishable from BD theory in solar-system experiments.

Gravitational Faraday effect in conformally stationary spacetimes

For conformally stationary spacetimes it is possible to formulate the geometric optics approximation of light propagation purely in terms of the geometry of the three-dimensional manifold M consisting of the integral curves of the conformal Killing vector field. In this framework they derive the transport law for the polarization plane in M. If the conformal Killing field has a non-vanishing twist, the polarization plane undergoes a rotation similar to the familiar Faraday rotation in a magnetic field. This so-called gravitational Faraday effect is of particular interest in the gravitational field of rotating matter where is is coupled to the angular momentum of this matter. Therefore, they illustrate their general results with three rotating matter examples, namely (i) an Ozsvath-Schucking spacetime; (ii) the gravitational field outside a rotating body and (iii) a Kerr black hole embedded into a Robertson-Walker cosmos. Thereby they roughly estimate the observability of the gravitational Faraday effect in solar system experiments and in connection with the gravitational lens effect.

Bounds on oscillating physics from solar system experiments

We show that the model based on oscillating atomic lines which has recently been proposed to explain the observed periodicity in the galaxy distribution in a pencil beam survey is in effect ruled out by the experiment of Braginskii and Panov.

Trapping the Kaluza-Klein scalar

The Kaluza-Klein unified theory predicts the existence of a Brans-Dicke type scalar field withω = 0. Solar system experiments do, however, imply that gravitational scalar fields must be suppressed either by a very weak coupling to matter (ω > 500) or a self-interaction. Here the consequences of a self-interaction potential of the Kaluza-Klein scalar are investigated. By suppressing the scalar field in this way, the one-body metric reduces to the Schwarzschild solution. The cosmologies of the scalar-tensor model are, however, very different from cosmologies of Einstein's theory, since here the time evolution of the cosmic scale-factor is determined only by the initial conditions. These may be chosen so that the theory is compatible with the hypothesis of primordial nucleosynthesis.

A Note on Lan's Generalised Theory of Gravitation

Lau has recently proposed a generalised theory of gravitation incorporating time-dependent cosmological and gravitational terms which is consistent with Dirac's large numbers hypothesis. It is shown that all vacuum solutions in this theory are identical to those of Einstein's theory with a cosmological constant. In particular, solar system experiments cannot be used to test the theory.

Cosmological models in Barker's theory of gravitation.

A systematic and exhaustive study of homogeneous and isotropic cosmological models in Barker's theory of gravitation is reported, where present values of dynamical functions are consistent with astronomical observations and solar-system experiments. Except in the special case where ${q}_{0}$=${\ensuremath{\Omega}}_{0}$/2, which constitutes a region of zero measure in the allowed zone of the (${q}_{0}$,${\ensuremath{\Omega}}_{0}$) plane, the age of the Universe in these cosmological models is less than the age of old globular clusters. Other specific features of Barker's cosmologies are also presented.

The Homogeneous, Isotropic Universe in New General Relativity

The standard model of the universe is based on the cosmological principle, namely on the assumption that the universe is homogeneous and isotropic in the large scale. This principle determines the metric structure of the universe uniquely, exc.ept for the radius of the universe the time evolution of which is described by the gravitational field equation. l ) It is usually assumed that the law of gravity is described by general relativity and that the evolution of the universe is governed by the Einstein equation. 2 ) This standard model of the universe is known to provide us with a theoretical framework of cosmology consistent with all the observational data. 3 ) The Riemann space-time underlying general relativity is characterized by the cur­ vature tensor alone with the torsion tensor being identically vanishing. Therefore the Riemann space-time is regarded as the vanishing-torsion limit of the Riemann-Cartan space-time: The latter space-time is characterized by the curvature tensor and the torsion tensor. 4 ) Another interesting, limiting case of the Riemann-Cartan space-time is the Weitzenbock space-time in which the curvature tensor is identically vanishing. The Weitzenbock space-time admits absolute parallelism by definition, and its basic entity is a quadruplet of linearly independent parallel vector fields (or simply, parallel vector fields). New general relativity is a gravitational theory based on the Weitzenbock space-time, attributing gravitation to the torsion of space-time.*)'S)-S) It has been shown that this theory is compatible with all the solar system experiments. S ) The purpose of this paper is to apply new general relativity to cosmology. We shall obtain the general expression for the parallel vector fields by requiring the cosmological principle, and then use the gravitational field equation to get the expansion equation of the homogeneous, isotropic universe.

Equations of motion of test bodies in a spherically symmetric, static gravitational field

We consider a class of theories of gravity in which the motion of test particles is governed by the path equation (with respect to a general affine connection Г). When we restrict attention to a spherically symmetric, static gravitational field, the path equation is characterized by three arbitrary functions of the gravitational field (as opposed to two in the case of metric theories where Г={ }). We find that there are essentially only two constraints on the three functions by appealing to solar system experiments. Therefore, we must supplement the equation of motion with other physical laws to obtain a value for the third arbitrary function (this, of course, is not necessary in the case of metric theories). If we consider theories in which both Г andg play a physical role we find in certain circumstances that this “third” condition is sufficient to prove that the theories under investigation reduce to their “metric” form.

Production of primordial helium and deuterium as a strong-field test of gravitation theory

view Abstract Citations (2) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Production of primordial helium and deuterium as a strong-field test of gravitation theory Falik, D. ; Opher, R. Abstract It is noted that a fundamental weak-field test of a theory of gravitation is that it satisfies the Parameterized Post-Newtonian (PPN) parameters determined by solar system experiments. The production of primordial helium and deuterium in the big bang is seen as a test of a gravitational theory in the strong-field approximation, and it is suggested that this test be used along with the PPN parameters. The test is applied to Rosen's bi-metric theory of gravitation, and for a wide class of models of this theory it is shown that essentially no primordial helium or deuterium is produced. Publication: The Astrophysical Journal Pub Date: January 1981 DOI: 10.1086/158560 Bibcode: 1981ApJ...243....8F Keywords: Big Bang Cosmology; Deuterium; Gravitation Theory; Helium; Nuclear Fusion; Relativity; Astronomical Models; Bimetric Theories; Field Strength; Gravitational Fields; Astrophysics full text sources ADS |

Scalar tensor theories and variable rest masses

Considers a large class of scalar tensor theories which are derivable from a certain parametrised Lagrangian. The field equations are found and solved exactly for spherical symmetry. The author identifies the parameters appearing in this solution and use it to calculate the experimental predictions of this class of theories. This class contains a large variety of theories including general relativity, the Brans-Dicke theory, and theories with variable rest masses. Particular attention is paid to whether or not variable rest-mass effects are observable. It is found that such effects are observable even if the theory is transformed back to laboratory units and cannot be ruled out by the standard solar system experiments.

General relativity without general relativity

Recently one of us proposed a general theory of variable rest masses (VMT) compatible with post-Newtonian solar-system experiments for a wide range of its two parameters $r$ and $q$, provided the asymptotic value of its fundamental field $f$ is in a certain narrow range. Here we show that the stationary matter-free black-hole solutions of the VMT are identical to those of general relativity. In addition, for $r<0$ and $q>0$ (part of the range mentioned), relativistic neutron-star models in the VMT are very similar to their general-relativistic counterparts. Thus experimental discrimination between the two theories in the strong-field limit seems unfeasible. We show that in all isotropic cosmological models of the VMT capable of describing the present epoch, the Newtonian gravitational constant ${G}_{N}$ is positive throughout the cosmological expansion. There exist nonsingular VMT cosmological solutions; this is an advantage the VMT has over general relativity. For $r<0$ and $q>0$ all VMT cosmological models converge to their general-relativistic analogs at late times. As a consequence the asymptotic $f$ attains just the required values to guarantee agreement of the VMT with post-Newtonian experiments. The VMT with $r<0$ and $q>0$ predicts a positive Nordtvedt-effect coefficient. It also predicts that ${G}_{N}$ is currently decreasing on a time scale which could be long compared to the Hubble time. Verification of these predictions would rule out general relativity; its most natural replacement would be the VMT with $r<0$ and $q>0$, and not a generic scalar-tensor theory. The success of general relativity in most respects could then be understood because the VMT with $r<0$ and $q>0$ mimics it. Because of this, general relativity could still be used, for most purposes, as a good approximation to the correct gravitational theory.

Possible test of the strong principle of equivalence

view Abstract Citations (5) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Possible test of the strong principle of equivalence. Brecher, K. Abstract It is suggested that redshift determinations of X-ray and gamma-ray lines produced near the surface of neutron stars which arise from different physical processes could provide a significant test of the strong principle of equivalence for strong gravitational fields. As a complement to both the high-precision weak-field solar-system experiments and the cosmological time-variation searches, such observations could further test the hypothesis that physics is locally the same at all times and in all places. Publication: The Astrophysical Journal Pub Date: February 1978 DOI: 10.1086/182619 Bibcode: 1978ApJ...219L.117B Keywords: Equivalence; Gravitational Effects; Neutron Stars; Red Shift; Relativity; Stellar Gravitation; Field Theory (Physics); Gamma Ray Astronomy; Gravitational Fields; Theoretical Physics; X Ray Astronomy; X Ray Spectra; Astrophysics; Neutron Stars; Relativity Theory: Tests full text sources ADS | data products SIMBAD (2)

Are particle rest masses variable? Theory and constraints from solar system experiments

We consider the possibility that particle rest masses may vary in spacetime. According to arguments originated by Dicke, if this is the case various null experiments indicate that all masses vary in the same way. Their variation relative to the Planck-Wheeler mass defines a universal scalar rest-mass field. We construct the relativistic dynamics for this field based on very general assumptions. In addition, we assume Einstein's equations to be valid in Planck-Wheeler units. A special case of the theory coincides with Dicke's reformulation of Brans-Dicke theory as general relativity with variable rest masses. In the general case the rest-mass field is some power $r$ of a scalar field which obeys an ordinary scalar equation with coupling to the curvature of strength $q$. The $r$ and $q$ are the only parameters of the theory. Comparison with experiment is facilitated by recasting the theory into units in which rest masses are constant, the Planck-Wheeler mass varies, and the metric satisfies the equations of a small subset of the scalar-tensor theories of gravitation. The results of solar system experiments, usually used to test general relativity, are here used to delimit the acceptable values of $r$ and $q$. We conclude that if cosmological considerations are not invoked, then the solar-system experiments do not rule out the possibility of rest-mass variability. That is, there are theories which agree with all null and solar-system experiments, and yet contradict the strong equivalence principle by allowing rest masses to vary relative to the Planck-Wheeler mass. We show that the field theory of the rest-mass field can be quantized and interpreted in terms of massless scalar quanta which interact very weakly with matter. This explains why they have not turned up in high-energy experiments. In future reports we shall investigate the implications of various cosmological and astrophysical data for the theory of variable rest masses. The ultimate goal is a firm decision on whether rest masses vary or not.

Dipole gravitational radiation in Rosen's theory of gravity - Observable effects in the binary system PSR 1913+16

It is shown that Rosen's (1973) bimetric theory of gravity predicts the emission of dipole gravitational radiation from binary systems containing neutron stars, such as the binary pulsar PSR 1913+16, which causes rapid changes in orbital period. The theory also predicts sizable corrections to masses inferred from orbital data and periastron-shift data. It is demonstrated that this prediction is inconsistent with the observed upper limit on period changes unless the system consists of two neutron stars whose masses differ by less than 0.3 solar mass, or a neutron star of mass less than 0.4 solar mass and a companion which must be a rapidly rotating white dwarf or a helium main-sequence star. Because Rosen's theory is in agreement with all solar-system experiments to date, this represents a feasible test of its viability.