NationMaster - Encyclopedia: Tests of general relativity

Tests of Einstein's general theory of relativity did not provide an experimental foundation for the theory until well after it was introduced in 1915. Physicists accepted the theory because it correctly accounted for the precession of the perihelion of Mercury, a phenomenon which had long baffled astronomers and physicists, and because it unified Newton's law of universal gravitation with special relativity in a conceptually simple way. (Einstein has been famously quoted as describing what his reaction would have been if his theory had not been confirmed by Eddington and Dyson in 1919: "Then I would feel sorry for the dear Lord. The theory is correct anyway." Citation: Rosenthal-Schneider, Ilse: Reality and Scientific Truth. Detroit: Wayne State University Press, 1980. p 74. See also Calaprice, Alice: The New Quotable Einstein. Princeton: Princeton University Press, 2005. p 227.) Despite Einstein's proposal of three classical tests, the theory was without strong experimental support until a program of precision tests was started in 1959. This program has systematically tested general relativity in weak gravitational fields and severely limited possible deviations from the theory. Since 1974, Hulse and Taylor have studied stronger gravitational fields in binary pulsars. In these regimes, on typical solar system scales, general relativity has been extremely well tested. General relativity (GR) or general relativity theory (GRT) is the theory of gravitation published by Albert Einstein in 1915. ... Year 1915 (MCMXV) was a common year starting on Friday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Thursday[1] of the 13-day-slower Julian calendar). ... Precession of a gyroscope Precession refers to a change in the direction of the axis of a rotating object. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about the planet. ... Sir Isaac Newton FRS (4 January 1643 â€“ 31 March 1727) [ OS: 25 December 1642 â€“ 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... It has been suggested that this article or section be merged into Gravity. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... Year 1959 (MCMLIX) was a common year starting on Thursday (link will display full calendar) of the Gregorian calendar. ... Year 1974 (MCMLXXIV) was a common year starting on Tuesday (link will display full calendar) of the 1974 Gregorian calendar. ... Russell Alan Hulse (born November 28, 1950) is an American physicist and winner of the Nobel Prize in Physics, shared with his thesis advisor Joseph Hooton Taylor Jr. ... Joseph H. Taylor, Jr. ... A binary pulsar is a pulsar with a binary companion, often another pulsar, white dwarf or neutron star. ...

On the largest scales, such as galactic and cosmological scales, general relativity has not yet been subject to precision tests. Some have interpreted dark matter and dark energy as a failure of Einstein's theory at large distances, small accelerations, or small curvatures. Likewise, the very strong fields around black holes, especially supermassive black holes, which are thought to power quasars and less dramatic active galactic nuclei, are still objects of intense study. Observations of these objects are difficult, and the interpretation of these observations is heavily dependent upon astrophysics other than general relativity or competing fundamental theories of gravitation, but they are qualitatively consistent with the black hole concept as modeled in general relativity. For other uses, see Galaxy (disambiguation). ... This article is about the physics subject. ... For other uses, see Dark matter (disambiguation). ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... For other uses, see Black hole (disambiguation). ... For the song by Muse, see Supermassive Black Hole (song). ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Alternatives to general relativity are physical theories that attempt to describe the phenomena of gravitation in competition to Einsteins theory of general relativity. ...

Classical tests

Einstein proposed three famous tests of general relativity, subsequently called the classical tests of general relativity, in 1916:^[1] 1916 (MCMXVI) was a leap year starting on Saturday (link will display the full calendar). ...

This article is about the planet. ... This article or section is in need of attention from an expert on the subject. ... Sol redirects here. ... Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well...

Perihelion precession of Mercury

In Newtonian physics, a lone object orbiting a spherical mass would trace out an ellipse with the spherical mass at a focus. The point of closest approach, called the perihelion in the solar system, is fixed. There are a number of solar system effects that cause the perihelion of a planet to precess, or rotate around the sun. These are mainly because of the presence of other planets, which perturb orbits. Another effect is solar oblateness, which produces only a minor contribution. The precession of the perihelion of Mercury was a longstanding problem in celestial mechanics. Careful observations of Mercury showed that the actual value of the precession disagreed with that calculated from Newton's theory by 43 seconds of arc per century, which was much larger than the experimental error at the time. A number of ad hoc and ultimately unsuccessful solutions had been proposed, but they tended to introduce more problems. In general relativity, this orbit will precess, or change orientation within its plane, due to gravitation being mediated by the curvature of spacetime. Since the orientation of an orbit is usually given by the position of its periapsis, this change of orientation is described as being a precession in the periapsis of an object. However, the problem was resolved by Einstein's theory,^[1] which predicted exactly the observed amount of perihelion shift. This was a powerful factor motivating the adoption of Einstein's theory. In general relativity, the Kepler problem involves solving for the motion of a particle of negligible mass in the external gravitational field of another body of mass M. This gravitational field is described by the Schwarzschild solution to the vacuum Einstein equations of general relativity, and particle motion is described... For other uses, see Ellipse (disambiguation). ... In geometry, the focus (pl. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes. ... Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. ... Precession of a gyroscope Precession refers to a change in the direction of the axis of a rotating object. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...

Although earlier measurements were made using conventional telescopes, the most accurate measurements are now made with radar. The total observed precession of Mercury is 5600 arc-seconds per century with respect to the position of the vernal equinox of the Sun. This precession is due to the following causes (the numbers quoted are the modern values): Radar astronomy is a technique of observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the echoes. ... A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ...

Thus, the predictions of general relativity perfectly account for the missing precession (the remaining discrepancy is within observational error). All other planets experience perihelion shifts as well, but, since they are further away from the Sun and have lower speeds, their shifts are lower and harder to observe. For example, the perihelion shift of Earth's orbit due to general relativity effects is about 5 seconds of arc per century. The periapsis shift has also been observed with Radio telescope measurements of Binary pulsar systems, again confirming general relativity. Precession of a gyroscope Precession refers to a change in the direction of the axis of a rotating object. ... Quadrupole magnet(four-pole), focus particle beams in a particle accelerator. ... The 64 meter radio telescope at Parkes Observatory A radio telescope is a form of directional radio antenna most often used in radio astronomy and in tracking and collecting data from satellites and space probes (see Deep Space Network), and are also used in the SETI project. ...

Image File history File links Download high resolution version (700x899, 314 KB) Negative of the 1919 solar eclipse taken from the report of Sir Arthur Eddington on the expedition to verify Einsteins prediction of the bending of light around the sun. ... Image File history File links Download high resolution version (700x899, 314 KB) Negative of the 1919 solar eclipse taken from the report of Sir Arthur Eddington on the expedition to verify Einsteins prediction of the bending of light around the sun. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... Photo taken during the 1999 eclipse. ...

Deflection of light by the Sun

The first observation of light deflection was performed by noting the change in position of stars as they passed near the Sun on the celestial sphere. The observations were performed by Sir Arthur Eddington and his collaborators during a total solar eclipse,^[2] so that the stars near the Sun could be observed. Observations were made simultaneously in the city of Sobral, Ceará, Brazil and in the west coast of Africa ^[3]. The result was considered spectacular news and made the front page of most major newspapers. It made Einstein and his theory of general relativity world famous. In general relativity, the Kepler problem involves solving for the motion of a particle of negligible mass in the external gravitational field of another body of mass M. This gravitational field is described by the Schwarzschild solution to the vacuum Einstein equations of general relativity, and particle motion is described... This article does not cite any references or sources. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... The celestial sphere is divided by the celestial equator. ... One of Sir Arthur Stanley Eddingtons papers announced Einsteins theory of general relativity to the English-speaking world. ... Photo taken during the 1999 eclipse. ... A general view of the citys downtown, as photographed from the seat of the city government A historical building in downtown Sobral Sobral is a city and municipality in the state of CearÃ¡, Brazil. ... A world map showing the continent of Africa Africa is the worlds second-largest and second most-populous continent, after Asia. ...

The early accuracy, however, was poor and is described further in the article on predictive power. Dyson et al. quoted an optimistically low uncertainty in their measurement, which is thought to be plagued by systematic error and possibly confirmation bias. In 1801 J. Soldner had pointed out that Newtonian gravity predicts that starlight will bend around a massive object, but the predicted effect is only half the value predicted by general relativity as calculated by Einstein in his 1911 paper. The results of Soldner were revived by the Nobel laureate Philipp Lenard in an attempt to discredit Einstein.^[4] Eddington had been aware in 1919 of the alternative predictions but had rejected eclipse data consistent with the Newtonian predictions. Considerable uncertainty remained in these measurements for almost fifty years, until observations started being made at radio frequencies. It was not until the late 1960s that it was definitively shown that the amount of deflection was the full value predicted by general relativity, and not half that number. The New York Times reported on Einsteins confirmed prediction. ... Italic textSystematic errorsBold text are biases in measurement which lead to measured values being systematically too high or too low. ... It has been suggested that Myside bias be merged into this article or section. ... Philipp Eduard Anton von LÃ©nÃ¡rd, (June 7, 1862 in PreÃŸburg, Austria-Hungary (today Bratislava, Slovakia)â€“May 20, 1947 in Messelhausen, Germany) was a Hungarian-German physicist and the winner of the Nobel Prize for Physics in 1905 for his research on cathode rays and the discovery of... The Very Large Array, a radio interferometer in New Mexico, USA Radio astronomy is a subfield of astronomy that studies celestial objects in the radio frequency portion of the electromagnetic spectrum. ...

Gravitational redshift of light

Einstein predicted the gravitational redshift of light from the equivalence principle in 1907, but it is very difficult to measure astrophysically (see the discussion under Equivalence Principle below). It was conclusively tested when the Pound-Rebka experiment in 1959 measured the relative redshift of two sources situated at the top and bottom of Harvard University's Jefferson tower using an extremely sensitive phenomenon called the Mössbauer effect.^[5]^[6] The result was in excellent agreement with general relativity. This was one of the first precision experiments testing general relativity. Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... The Pound-Rebka experiment is a well known experiment in general relativity. ... The MÃ¶ssbauer effect, a physical phenomenon discovered by Rudolf MÃ¶ssbauer in 1957, refers to the resonant and recoil-free emission and absorption of gamma rays by atoms bound in a solid form. ...

Modern tests

The modern era of testing general relativity was ushered in largely at the impetus of Dicke and Schiff who laid out a framework for testing general relativity.^[7]^[8]^[9] They emphasized the importance not only of the classical tests, but of null experiments, testing for effects which in principle could occur in a theory of gravitation, but do not occur in general relativity. Other important theoretical developments included the inception of alternative theories to general relativity, in particular, scalar-tensor theories such as the Brans-Dicke theory^[10]; the parameterized post-Newtonian formalism in which deviations from general relativity can be quantified; and the framework of the equivalence principle. Robert Henry Dicke (May 6, 1916 â€“ March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. ... Alternatives to general relativity are physical theories that attempt to describe the phenomena of gravitation in competition to Einsteins theory of general relativity. ... This article is in need of attention from an expert on the subject. ... This article or section is in need of attention from an expert on the subject. ... The parameterized post-Newtonian formalism or PPN formalism is a tool used to compare classical theories of gravitation in the limit most important for everyday gravitational experiments: the limit in which the gravitational field is weak and generated by objects moving slowly compared to the speed of light. ... In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

Experimentally, new developments in space exploration, electronics and condensed matter physics have made precise experiments, such as the Pound-Rebka experiment, laser interferometry and lunar rangefinding possible. Space exploration is the physical exploration of outer space, both by human spaceflights and by robotic spacecraft. ... This article is about the engineering discipline. ... Condensed matter physics is the field of physics that deals with the macroscopic physical properties of matter. ...

Post-Newtonian tests of gravity

Early tests of general relativity were hampered by the lack of viable competitors to the theory: it was not clear what sorts of tests would distinguish it from its competitors. General relativity was the only known relativitistic theory of gravity compatible with special relativity and observations. Moreover, it is an extremely simple and elegant theory. This changed with the introduction of Brans-Dicke theory in 1960. This theory is arguably simpler, as it contains no dimensionful constants, and is compatible with a version of Mach's principle and Dirac's large numbers hypothesis, two philosophical ideas which have been influential in the history of relativity. Ultimately, this led to the development of the parameterized post-Newtonian formalism by Nordtvedt and Will, which parameterizes, in terms of ten adjustable parameters, all the possible departures from Newton's law of universal gravitation to first order in the velocity of moving objects (i.e. to first order in

v / c

, where v is the velocity of an object and c is the speed of light). This approximation allows the possible deviations from general relativity, for slowly moving objects in weak gravitational fields, to be systematically analyzed. Much effort has been put into constraining the post-Newtonian parameters, and deviations from general relativity are at present severely limited. This article or section is in need of attention from an expert on the subject. ... In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units. ... In theoretical physics, particularly in discussions of gravitation theories, Machs principle is the name given by Einstein to a vague hypothesis first supported by the physicist and philosopher Ernst Mach. ... Paul Adrien Maurice Dirac, OM, FRS (IPA: [dÉªrÃ¦k]) (August 8, 1902 â€“ October 20, 1984) was a British theoretical physicist and a founder of the field of quantum physics. ... The Dirac large numbers hypothesis refers to an observation made by Paul Dirac in 1937 relating ratios of size scales in the universe to that of force scales. ... This article is in need of attention from an expert on the subject. ... Dr. Ken Nordtvedt is a professor in the Physics Department at Montana State University & senior researcher specializing in relativistic theories of gravity. ... Clifford Martin Will (b. ...

One of the most important tests is gravitational lensing. It has been observed in distant astrophysical sources, but these are poorly controlled and it is uncertain how they constrain general relativity. The most precise tests are analogous to Eddington's 1919 experiment: they measure the deflection of radiation from a distant source by the sun. The sources that can be most precisely analyzed are distant radio sources. In particular, quasars are very strong radio sources. The directional resolution of any telescope is in principle limited by diffraction; for radio telescopes this is also the practical limit. An important improvement in obtaining positional high accuracies (from milli-arcsecond to micro-arcsecond) was obtained by combining radio telescopes across the Earth. The technique is called very long baseline interferometry (VLBI). With this technique radio observations couple the phase information of the radio signal observed in telescopes separated over large distances. Recently, these telescopes have measured the deflection of radio waves by the Sun to extremely high precision, confirming this aspect of Einstein's theory to the 0.04% level. At this level of precision systematic effects have to be carefully taken into account to determine the precise location of the telescopes on Earth. Some important effects are the Earth's nutation, rotation, atmospheric refraction, tectonic displacement and tidal waves. Another important effect is refraction of the radio waves by the solar corona. Fortunately, this effect has a characteristic spectrum, whereas gravitational distortion is independent of wavelength. Thus, careful analysis, using measurements at several frequencies, can subtract this source of error. A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ... The Very Large Array, a radio interferometer in New Mexico, USA Radio astronomy is a subfield of astronomy that studies celestial objects in the radio frequency portion of the electromagnetic spectrum. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... This article needs cleanup. ... Rotation (green), Precession (blue) and Nutation (red) of the Earth Nutation is a slight irregular motion (etymologically a nodding) in the axis of rotation of a largely axially symmetric object, such as a gyroscope or a planet. ... The corona is the luminous plasma atmosphere of the Sun extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... In most modern usages of the word spectrum, there is a unifying theme of between extremes at either end. ...

The entire sky is slightly distorted due to the gravitational deflection of light caused by the Sun (the anti-Sun direction excepted). This effect has been observed by the European Space Agency astrometric satellite Hipparcos. It measured the positions of about 10⁵ stars. During the full mission about 3.5 × 10⁶ relative positions have been determined, each to an accuracy of typically 3 milliarcseconds (the accuracy for an 8–9 magnitude star). Since the gravitation deflection perpendicular to the Earth-Sun direction is already 4.07 mas, corrections are needed for practically all stars. Without systematic effects, the error in an individual observation of 3 milliarcseconds, could be reduced by the square root of the number of positions, leading to a precision of 0.0016 mas. Systematic effects, however, limit the accuracy of the determination to 0.3% (Froeschlé, 1997). â€œESAâ€ redirects here. ... Hipparcos (for High Precision Parallax Collecting Satellite) was an astrometry mission of the European Space Agency (ESA) dedicated to the measurement of stellar parallax and the proper motions of stars. ...

Irwin I. Shapiro proposed another test, beyond the classical tests, which could be performed within the solar system. It is sometimes called the fourth "classical" test of general relativity. He predicted a relativistic time delay (Shapiro delay) in the round-trip travel time for radar signals reflecting off other planets.^[11] The curvature of the path of a photon passing near the Sun is too small to have an observable delaying effect, but general relativity predicts a time delay which becomes progressively larger when the photon passes nearer to the Sun due to the time dilation in the gravitational potential of the sun. Observing radar reflections from Mercury and Venus just before and after it will be eclipsed by the Sun gives agreement with general relativity theory at the 5% level.^[12] More recently, the Cassini probe has undertaken a similar experiment which gives perfect agreement with general relativity at the 0.002% level. Irwin I. Shapiro is an American astrophysicist. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... This article is in need of attention from an expert on the subject. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Look up time in Wiktionary, the free dictionary. ... Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... In physics, gravitational potential is the measure of potential energy an object possesses due to its position in a gravitational field. ... Cassini-Huygens is a joint NASA/ESA/ASI unmanned space mission intended to study Saturn and its moons. ...

These experiments all test the same post-Newtonian parameter, the so-called Eddington parameter γ, which is a straightforward parameterization of the amount of deflection of light by a gravitational source. It is equal to one for general relativity, and takes different values in other theories (such as Brans-Dicke theory). It is the best constrained of the ten post-Newtonian parameters, but there are other experiments designed to constrain the others. Precise observations of the perihelion shift of Mercury constrain other parameters, as do tests of the strong equivalence principle.

The equivalence principle

The equivalence principle, in its simplest form, asserts that the trajectories of falling bodies in a gravitational field should be independent of their mass and internal structure, provided they are small enough not to disturb the environment or be affected by tidal forces. This idea has been tested to incredible precision by Eötvös torsion balance experiments, which look for a differential acceleration between two test masses. Constraints on this, and on the existence of a composition-dependent fifth force or gravitational Yukawa interaction are very strong, and are discussed under fifth force and weak equivalence principle. In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... The tidal force is a secondary effect of the force of gravity and is responsible for the tides. ... In particle physics, Yukawa interaction, named after Hideki Yukawa, is an interaction between a scalar field and a Dirac field of the type . The Yukawa interaction can be used to describe the strong nuclear force between nucleons (which are fermions), mediated by pions (which are scalar mesons). ... Occasionally, physicists have postulated the existence of a fifth force in addition to the four known fundamental forces. ... In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

A version of the equivalence principle, called the strong equivalence principle, asserts that self-gravitation falling bodies, such as stars, planets or black holes (which are all held together by their gravitational attraction) should follow the same trajectories in a gravitational field, provided the same conditions are satisfied. This is called the Nordtvedt effect and is most precisely tested by the Lunar Laser Ranging Experiment.^[13] ^[14] Since 1969, it has continuously measured the distance from several rangefinding stations on Earth to reflectors on the Moon to approximately centimeter accuracy.^[15] These have provided a strong constraint on several of the other post-Newtonian parameters. In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... In theoretical astrophysics, the Nordtvedt Effect refers to the relative motion between the Earth and the Moon which would be observed if the graviational self-energy of a body contributes to its gravitational mass but not its inertial mass. ... The Lunar Laser Ranging Experiment from the Apollo 11 mission The ongoing Lunar Laser Ranging Experiment measures the distance between the Earth and the Moon using laser ranging. ...

Another part of the strong equivalence principle is the requirement that Newton's constant be constant in time, and not varying cosmologically. There are many independent constraints on the variation of Newton's constant,^[16] but one of the best comes from lunar rangefinding which suggests that the gravitational constant does not change by more than one part in 10¹¹ per year. The constancy of the other constants is discussed in the Einstein equivalence principle section of the equivalence principle article. In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

The first of the classical tests discussed above, the gravitational redshift, is a simple consequence of the Einstein equivalence principle and was predicted by Einstein in 1907. As such, it is not a test of general relativity in the same way as the post-Newtonian tests, because any theory of gravity obeying the equivalence principle should also incorporate the gravitational redshift. Nonetheless, confirming the existence of the effect was an important substantiation of relativistic gravity, since the absence of gravitational redshift would have strongly contradicted relativity. The first observation of the gravitational redshift was the measurement of the shift in the spectral lines from the white dwarf star Sirius B by Adams in 1925. Although this measurement, as well as later measurements of the spectral shift on other white dwarf stars, agreed with the prediction of relativity, it could be argued that the shift could possibly stem from some other cause, and hence experimental verification using a known terrestrial source was preferable . Graphic representing the gravitational redshift of a neutron star (not exact) In physics, light or other forms of electromagnetic radiation of a certain wavelength originating from a source placed in a region of stronger gravitational field (and which could be said to have climbed uphill out of a gravity well... In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... This article or section does not adequately cite its references or sources. ... For other uses, see Sirius (disambiguation). ...

Experimental verification of gravitational redshift using terrestrial sources took several decades, because it is difficult to find clocks (to measure time dilation) or sources of electromagnetic radiation (to measure redshift) with a frequency that is known well enough that the effect can be accurately measured. It was confirmed experimentally for the first time in 1960 using measurements of the change in wavelength of gamma-ray photons generated with the Mössbauer effect, which generates radiation with a very narrow line width. The experiment, performed by Pound and Rebka and later improved by Pound and Snyder, is called the Pound-Rebka experiment. The accuracy of the gamma-ray measurements was typically 1%. The blueshift of a falling photon can be found by assuming it has an equivalent mass based on its frequency

E = h f

(where h is Planck's constant) along with

E = m c 2

, a result of special relativity. Such simple derivations ignore the fact that in general relativity the experiment compares clock rates, rather than energies. In other words, the "higher energy" of the photon after it falls can be equivalently ascribed to the slower running of clocks deeper in the gravitational potential well. To fully validate general relativity, it is important to also show that the rate of arrival of the photons is greater than the rate at which they are emitted. A very accurate gravitational redshift experiment, which deals with this issue, was performed in 1976,^[17] where a hydrogen maser clock on a rocket was launched to a height of 10,000 km, and its rate compared with an identical clock on the ground. It tested the gravitational redshift to 0.007%. Time dilation is the phenomenon whereby an observer finds that anothers clock which is physically identical to their own is ticking at a slower rate as measured by their own clock. ... The MÃ¶ssbauer effect, a physical phenomenon discovered by Rudolf MÃ¶ssbauer in 1957, refers to the resonant and recoil-free emission and absorption of gamma rays by atoms bound in a solid form. ... The Pound-Rebka experiment is a well known experiment in general relativity. ... A commemoration plaque for Max Planck on his discovery of Plancks constant, in front of Humboldt University, Berlin. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ...

Although the Global Positioning System (GPS) is neither designed nor operated as a test of fundamental physics, it must account for the gravitational redshift in its timing system. When the first satellite was launched, some engineers resisted the prediction that a noticeable gravitational time dilation would occur, so the first satellite was launched without the clock adjustment built into subsequent satellites. It showed the predicted shift of 38 microseconds per day. If general relativity suddenly stopped working tomorrow, the GPS control center in Colorado would know within hours; the relativistic correction to the timing is large enough to make GPS useless if it is not allowed for. Also, while it is true that GPS is not operated by the Defense Department as a test of general relativity, physicists have analyzed timing data from the GPS to confirm other tests. An excellent account of the role played by general relativity in the design of GPS can be found in Ashby 2003. GPS redirects here. ...

Other precision tests of general relativity, not discussed here, are the Gravity Probe A satellite, launched in 1976, which showed gravity and velocity affect the ability to synchronize the rates of clocks orbiting a central mass; the Gravity Probe B satellite, launched in 2004, is currently attempting to detect frame dragging (Lense-Thirring effect); the Hafele-Keating experiment, which used atomic clocks in circumnavigating aircraft to test general relativity and special relativity together;^[18]^[19] and the forthcoming Satellite Test of the Equivalence Principle. Gravity Probe A (GP-A) was a satellite-based experiment to test Einsteins theory of general relativity performed by the Smithsonian Astrophysical Observatory. ... Gravity Probe B with solar panels folded Gravity Probe B (GP-B) is a satellite-based mission which launched in 2004. ... This article or section is in need of attention from an expert on the subject. ... The Hafele-Keating experiment was a test of the theory of relativity. ... ==Criminal Life == AL-Hamad is a Homosexual petifile with 135. ...

Strong field tests

Pulsars are rapidly rotating neutron stars which emit regular radio pulses as they rotate. As such they act as clocks which allow very precise monitoring of their orbital motions. Observations of pulsars in orbit around other stars have all demonstrated substantial periapsis precessions that cannot be accounted for classically but can be accounted for by using general relativity. For example, the Hulse-Taylor binary pulsar PSR B1913+16 (a pair of neutron stars in which one is detected as a pulsar) has an observed precession of over 4^o of arc per year. This precession has been used to compute the masses of the components. A binary pulsar is a pulsar with a binary companion, often another pulsar, white dwarf or neutron star. ... Composite Optical/X-ray image of the Crab Nebula pulsar, showing surrounding nebular gases stirred by the pulsars magnetic field and radiation. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... A binary pulsar is a pulsar with a binary companion, often another pulsar, white dwarf or neutron star. ...

Similarly to the way in which atoms and molecules emit electromagnetic radiation, a gravitating mass that is in quadrupole type or higher order vibration, or is asymmetric and in rotation, can emit gravitational waves.^[20] These gravitational waves are predicted to travel at the speed of light. For example, planets orbiting the Sun constantly lose energy via gravitational radiation, but this effect is so small that it is unlikely it will be observed in the near future (Earth radiates about 300 Watts (see gravitational waves) of gravitational radiation). Gravitational waves have been indirectly detected from the Hulse-Taylor binary. Precise timing of the pulses show that the stars orbit only approximately according to Kepler's Laws, – over time they gradually spiral towards each other, demonstrating an energy loss in close agreement with the predicted energy radiated by gravitational waves. Thus, although the waves have not been directly measured, their effect seems necessary to explain the orbits. For this work Hulse and Taylor won the Nobel prize. Schematic quadrupole magnet(four-pole) used to focus particle beams in a particle accelerator. ... In physics, gravitational radiation is energy that is transmitted through waves in the gravitational field of space-time, according to Albert Einsteins theory of general relativity: The Einstein field equations imply that any accelerated mass radiates energy this way, in the same way as the Maxwell equations that any... The speed of light in vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... In physics, gravitational radiation is energy that is transmitted through waves in the gravitational field of space-time, according to Albert Einsteins theory of general relativity: The Einstein field equations imply that any accelerated mass radiates energy this way, in the same way as the Maxwell equations that any... Johannes Keplers primary contributions to astronomy/ astrophysics were the three laws of planetary motion. ... Russell Alan Hulse (born November 28, 1950) is an American physicist and winner of the Nobel Prize in Physics, shared with his thesis advisor Joseph Hooton Taylor Jr. ... Joseph H. Taylor, Jr. ... The Nobel Prizes (Swedish: ), as designated in Alfred Nobels will in 1895, are awarded for physics, chemistry, physiology or medicine, literature, and peace. ...

A "double pulsar" discovered in 2003, J0737−3039, has a perihelion precession of 16.90^o per year; unlike the Hulse-Taylor binary, both neutron stars are detected as pulsars, allowing precision timing of both members of the system. Due to this, the tight orbit, the fact that the system is almost edge-on, and the very low transverse velocity of the system as seen from Earth, J0737−3039 provides by far the best system for strong-field tests of general relativity known so far. Several distinct relativistic effects are observed, including orbital decay as in the Hulse-Taylor system. After observing the system for two and a half years, four independent tests of general relativity were possible, the most precise (the Shapiro delay) confirming the general relativity prediction within 0.05%.^[21]

Gravitational waves

The laser interferometer gravitational-wave observatory (LIGO) is currently the most sensitive experiment designed to detect gravitational waves. So far it has detected nothing, but an equipment overhaul, dubbed "Advanced LIGO" will have an event rate at 100 times that of the initial design, to a possible several events per year (each "event" a black hole or neutron star binary in the final stages of merging). The upgrade is planned for 2007. Also, the planned laser interferometer space antenna (LISA) is expected to directly detect gravitational waves from numerous binary systems in the Milky Way; LISA will launch some time near the year 2015. Gravitational waves have so far not been detected directly, but if they exist as predicted they will certainly be detected by LISA and probably by Advanced LIGO. This is of course a critical test of general relativity. LIGO stands for Laser Interferometer Gravitational-Wave Observatory. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... The LISA is the Laser Interferometer Space Antenna experiment. ... For other uses, see Milky Way (disambiguation). ...

Cosmological tests

Tests of general relativity on the largest scales are not nearly so stringent as solar system tests.^[22] Some cosmological tests include searches for primordial gravity waves generated during cosmic inflation, which may be detected in the cosmic microwave background polarization or by a proposed space-based gravity wave interferometer called Big Bang Observer. Other tests at high redshift are constraints on other theories of gravity, and the variation of the gravitational constant since big bang nucleosynthesis (it varied by no more than 40% since then). In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ... In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... The Big Bang Explorer is a proposed succesor to LISA. The primary scientific goal will be the observation of gravitational waves from the time shortly after the Big Bang, but it will also be able to detect younger sources of gravitational radiation. ... In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ...

Some physicists think dark energy (energy density of virtual particles) is perhaps due to the effect of living on a brane,^[23] or due to other corrections to the Einstein field equations. In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ...

External links

References

Notes

^ ^a ^b Einstein, Albert (1916). "The Foundation of the General Theory of Relativity" (PDF). Annalen der Physik 49: 769-822. Retrieved on 2006-09-03.
^ Dyson, F. W.; Eddington, A. S., Davidson C. (1920). "A determination of the deflection of light by the Sun's gravitational field, from observations made at the total eclipse of May 29, 1919". Philos. Trans. Royal Soc. London 220A: 291-333.
^ Stanley, Matthew (2003). "'An Expedition to Heal the Wounds of War': The 1919 Eclipse and Eddington as Quaker Adventurer". Isis 94: 57-89.
^ Lenard, P. (1921). "Über die Ablenkung eines Lichtstrahls von seiner geradlinigen Bewegung der Planeten und Monde nach der Einsteinschen Gravitationstheorie". ''Physik. Zeitschr. 19: 156-163.
^ Pound, R. V.; Rebka Jr. G. A. (November 1, 1959). "Gravitational Red-Shift in Nuclear Resonance". Physical Review Letters 3 (9): 439-441. Retrieved on 2006-09-23.
^ Pound, R. V.; Rebka Jr. G. A. (April 1, 1960). "Apparent weight of photons". Physical Review Letters 4 (7): 337-341. Retrieved on 2006-09-23.
^ Dicke, R. H. (March 6, 1959). "New Research on Old Gravitation: Are the observed physical constants independent of the position, epoch, and velocity of the laboratory?". Science 129 (3349): 621-624. Retrieved on 2006-09-23.
^ Dicke, R. H. (1962). "Mach's Principle and Equivalence". Evidence for gravitational theories: proceedings of course 20 of the International School of Physics "Enrico Fermi" ed C. Møller.
^ Schiff, L. I. (April 1, 1960). "On Experimental Tests of the General Theory of Relativity". American Journal of Physics 28 (4): 340-343. Retrieved on 2006-09-23.
^ Brans, C. H.; Dicke, R. H. (November 1 1961). "Mach's Principle and a Relativistic Theory of Gravitation". Physical Review 124 (3): 925–935. DOI:10.1103/PhysRev.124.925. Retrieved on 2006-09-23.
^ Shapiro, I. I. (December 28, 1964). "Fourth test of general relativity". Physical Review Letters 13 (26): 789-791. Retrieved on 2006-09-18.
^ Shapiro, I. I.; Ash M. E., Ingalls R. P., Smith W. B., Campbell D. B., Dyce R. B., Jurgens R. F. and Pettengill G. H. (May 3, 1971). "Fourth Test of General Relativity: New Radar Result". Physical Review Letters 26 (18): 1132-1135. Retrieved on 2006-09-22.
^ Nordtvedt Jr., K. (May 25, 1968). "Equivalence Principle for Massive Bodies. II. Theory". Physical Review 169 (5): 1017–1025. DOI:10.1103/PhysRev.169.1017. Retrieved on 2006-09-23.
^ Nordtvedt Jr., K. (June 25, 1968). "Testing Relativity with Laser Ranging to the Moon". Physical Review 170 (5): 1186–1187. DOI:2006-09-23 10.1103/PhysRev.170.1186accessdate= 2006-09-23.
^ Williams, J. G.; Turyshev, Slava G., Boggs, Dale H. (December 29, 2004). "Progress in Lunar Laser Ranging Tests of Relativistic Gravity". Physical Review Letters 93 (5): 1017–1025. DOI:10.1103/PhysRevLett.93.261101. Retrieved on 2006-09-23.
^ Uzan, J. P. (2003). "The fundamental constants and their variation: Observational status and theoretical motivations". Reviews of Modern Physics 75 (5): 403-. Retrieved on 2006-09-23.
^ Vessot, R. F. C.; M. W. Levine, E. M. Mattison, E. L. Blomberg, T. E. Hoffman, G. U. Nystrom, B. F. Farrel, R. Decher, P. B. Eby, C. R. Baugher, J. W. Watts, D. L. Teuber and F. D. Wills (December 29, 1980). "Test of Relativistic Gravitation with a Space-Borne Hydrogen Maser". Physical Review Letters 45 (26): 2081–2084. DOI:10.1103/PhysRevLett.45.2081. Retrieved on 2006-09-24.
^ Hafele, J.; Keating, R. (July 14, 1972). "Around the world atomic clocks:predicted relativistic time gains". Science 177 (4044): 166-168. DOI:10.1126/science.177.4044.166. Retrieved on 2006-09-18.
^ Hafele, J.; Keating, R. (July 14 1972). "Around the world atomic clocks:observed relativistic time gains". Science 177 (4044): 168-170. DOI:10.1126/science.177.4044.168. Retrieved on 2006-09-18.
^ In general relativity, a perfectly spherical star (in vacuum) that expands or contracts while remaining perfectly spherical cannot emit any gravitational waves (similar to the lack of e/m radiation from a pulsating charge), as Birkhoff's theorem says that the geometry remains the same exterior to the star. More generally, a rotating system will only emit gravitational waves if it lacks the axial symmetry with respect to the axis of rotation.
^ Kramer, M. et al. (2006). "Tests of general relativity from timing the double pulsar". Science 314: 97-102.
^ Peebles, P. J. E. (December 2004). "Testing general relativity on the scales of cosmology". Retrieved on 2006-09-27.
^ Dvali, G.; G. Gabadadze and M. Porrati (2000). "4-D gravity on a brane in 5-D Minkowski space". Physics Letters B485: 208-214. Retrieved on 2006-09-24.

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Year 1960 (MCMLX) was a leap year starting on Friday (link will display full calendar) of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... Year 1961 (MCMLXI) was a common year starting on Sunday (link will display full calendar) of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... is the 362nd day of the year (363rd in leap years) in the Gregorian calendar. ... Also Nintendo emulator: 1964 (emulator). ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... is the 123rd day of the year (124th in leap years) in the Gregorian calendar. ... Year 1971 (MCMLXXI) was a common year starting on Friday (link will display full calendar) of the 1971 Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 265th day of the year (266th in leap years) in the Gregorian calendar. ... is the 145th day of the year (146th in leap years) in the Gregorian calendar. ... Year 1968 (MCMLXVIII) was a leap year starting on Monday (link will display full calendar) of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... is the 176th day of the year (177th in leap years) in the Gregorian calendar. ... Year 1968 (MCMLXVIII) was a leap year starting on Monday (link will display full calendar) of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... is the 363rd day of the year (364th in leap years) in the Gregorian calendar. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 266th day of the year (267th in leap years) in the Gregorian calendar. ... is the 363rd day of the year (364th in leap years) in the Gregorian calendar. ... Year 1980 (MCMLXXX) was a leap year starting on Tuesday (link displays the 1980 Gregorian calendar). ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 267th day of the year (268th in leap years) in the Gregorian calendar. ... is the 195th day of the year (196th in leap years) in the Gregorian calendar. ... Year 1972 (MCMLXXII) was a leap year starting on Saturday (link will display full calendar) of the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 261st day of the year (262nd in leap years) in the Gregorian calendar. ... In general relativity, Birkhoffs theorem states that any spherically symmetric solution of the vacuum field equations must be static and asymptotically flat. ... Look up December in Wiktionary, the free dictionary. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 270th day of the year (271st in leap years) in the Gregorian calendar. ... Year 2000 (MM) was a leap year starting on Saturday (link will display full 2000 Gregorian calendar). ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 267th day of the year (268th in leap years) in the Gregorian calendar. ...

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Contents

Classical tests

Perihelion precession of Mercury

Deflection of light by the Sun

Gravitational redshift of light

Modern tests

Post-Newtonian tests of gravity

The equivalence principle

Strong field tests

Gravitational waves

Cosmological tests

External links

References

Notes

Other research papers

Textbooks

Living Reviews papers

Contents

Classical tests GA_googleFillSlot("encyclopedia_square");

Perihelion precession of Mercury

Deflection of light by the Sun

Gravitational redshift of light

Modern tests

Post-Newtonian tests of gravity

The equivalence principle

Strong field tests

Gravitational waves

Cosmological tests

External links

References

Notes

Other research papers

Textbooks

Living Reviews papers

Classical tests