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) will be found to be of longer wavelength when received by an observer in a region of weaker gravitational field. If applied to optical wave-lengths this manifests itself as a change in the colour of the light as the wavelength is shifted toward the red (making it: less energetic,longer in wavelength, and lower in frequency) part of the spectrum. This effect is called gravitational redshift and other spectral lines found in the light will also be shifted towards the longer wavelength, or "red," end of the spectrum. This shift can be observed along the entire electromagnetic spectrum. Image File history File links Gravitational_redshift_neutron_star. ... Image File history File links Gravitational_redshift_neutron_star. ... For the Hugo Award-winning story by Larry Niven, see Neutron Star (story). ... This is a discussion of a present category of science. ... This article does not cite any references or sources. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... A gravity well is the scientific/science fictional term for the distortion in space-time caused by a massive body such as a planet. ... For other uses, see Gravitation (disambiguation). ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ...

Light that has passed "downhill" into a region of stronger gravity shows a corresponding increase in energy, and is said to be gravitationally blueshifted. Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ...

Definition

Redshift is often denoted with the variable . Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ...

Where:

is the wavelength of the electromagnetic radiation (photon) as measured by the observer. is the wavelength of the electromagnetic radiation (photon) when measured at the source of emission. Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

Gravitational redshift, the displacement of light towards the red, can (for the case of a star) be predicted using the formula provided in the theory of General Relativity (Albert Einstein: Relativity - Appendix - Appendix III - The Experimental Confirmation of the General Theory of Relativity): For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... “Einstein” redirects here. ...

Where:

is the displacement of spectral lines due to gravity as viewed by a far away observer in free space. is Newton's gravitational constant (the variable used by Einstein himself). is the mass of the body which the light is escaping. is the speed of light. is the radius of the star you consider. Gravity is a force of attraction that acts between bodies that have mass. ... In physics, free space is a concept of electromagnetic theory, corresponding roughly to the vacuum, the baseline state of the electromagnetic field, or the replacement for the electromagnetic aether. ... According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... This article or section is in need of attention from an expert on the subject. ... “Lightspeed” redirects here. ...

Using the energy-momentum equation relating energy and wavelength of a photon, the gravitational redshift is equivalent to a loss of energy of the photon.

History

The gravitational weakening of light from high-gravity stars was predicted by John Michell in 1783, using Isaac Newton's concept of light as being composed of ballistic light corpuscles (see: emission theory). The effect of gravity on light was then explored by Laplace and Johann Georg von Soldner (1801) before Einstein rederived the idea from scratch in his 1911 paper on light and gravitation. John Michell (1724 – April 29, 1793) was an English natural philosopher and geologist, whose work was rediscovered in the 1970s. ... Sir Isaac Newton FRS (4 January 1643 – 31 March 1727) [ OS: 25 December 1642 – 20 March 1727][1] was an English physicist, mathematician, astronomer, natural philosopher, and alchemist. ... Emission theory (a. ... Pierre-Simon Laplace Pierre-Simon Laplace (March 23, 1749 – March 5, 1827) was a French mathematician and astronomer, the discoverer of the Laplace transform and Laplaces equation. ... Johann Georg von Soldner (16 July 1776 - 13 May 1833) was a German physicist, mathematician and astronomer. ... “Einstein” redirects here. ...

Einstein was accused by Philipp Lenard of plagiarism for not citing Soldner's earlier work - however, given that the idea had fallen so far into obscurity before Einstein resurrected it, it is entirely possible that Einstein was unaware of all previous work on the subject. In any case, Einstein went further and pointed out that a key consequence of gravitational shifts was gravitational time dilation. This was a genuinely new and revolutionary idea. Philipp Eduard Anton von Lénárd, (June 7, 1862 in Preßburg, Austria-Hungary (today Bratislava, Slovakia)–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... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ...

Important things to stress

• The receiving end of the light transmission must be located at a higher gravitational potential in order for gravitational redshift to be observed. In other words, the observer must be standing "uphill" from the source. If the observer is at a lower gravitational potential than the source, a gravitational blueshift can be observed instead.

• Tests done by many universities continue to support the existence of gravitational redshift.^{[citation needed]}

• Gravitational redshift is not only predicted by general relativity. Other theories of gravitation support gravitational redshift, although their explanations for why it appears vary.^{[citation needed]}

• Gravitational redshift does not assume the Schwarzschild metric solution to Einstein's field equation - in which the variable cannot represent the mass of any rotating or charged body.

In physics, gravitational potential is the measure of potential energy an object possesses due to its position in a gravitational field. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In physics, the Einstein field equation or Einstein equation is a differential equation in Einsteins theory of general relativity. ...

Initial verification

A number of experimenters initially claimed to have identified the effect using astronomical measurements, and the effect was eventually considered to have been finally idintified in the spectral lines of the star Sirius B by W.S. Adams in 1925. However, attempted verifications of the effect much before 1960's are now considered to be unsafe (C.M. Will), and the effect is now considered to have first been properly verified by the experiments of Pound, Rebka and Snider. Sirius B redirects here. ... Walter Sydney Adams (December 20, 1876 – May 11, 1956) was an American astronomer. ...

The Pound-Rebka experiment of 1959 definitively measured the gravitational redshift in spectral lines. This was documented by scientists of the Lyman Laboratory of Physics at Harvard University. A commonly-cited experimental verification is the Pound-Snider experiment of 1965. The Pound-Rebka experiment is a well known experiment in general relativity. ...

More information can be seen at Tests of general relativity. Tests of Einsteins general theory of relativity did not provide an experimental foundation for the theory until well after it was introduced in 1915. ...

Application

Gravitational redshift is studied in many areas of astrophysical research. Spiral Galaxy ESO 269-57 Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature, and chemical composition) of celestial objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ...

Exact Solutions

A table of exact solutions of the Einstein field equations consists of the following: 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. ...

The more often used exact equation for gravitational redshift applies to the case outside of a non-rotating, uncharged mass which is spherically symmetric. The equation is: It has been suggested that Deriving the Schwarzschild solution be merged into this article or section. ... In general relativity, the Kerr metric (or Kerr vacuum) describes the geometry of spacetime around a rotating massive body, such as a rotating black hole. ... In physics and astronomy, a Reissner-Nordström black hole, discovered by Gunnar Nordström and Hans Reissner, is a black hole that carries electric charge , no angular momentum, and mass . ... The Kerr-Newman metric is a solution of Einsteins general relativity field equation that describes the spacetime geometry around a charged (), rotating () black hole of mass m. ...

, where

• is the gravitational constant,
• is the mass of the object creating the gravitational field,
• is the radial coordinate of the observer (which is analogous to the classical distance from the center of the object, but is actually a Schwarzschild coordinate), and
• is the speed of light.

According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... This article or section is in need of attention from an expert on the subject. ... In General Relativity, Schwarzschild coordinates refers to the coordinate system of the Schwarzschild metric. ... “Lightspeed” redirects here. ...

Gravitational Redshift vs. Gravitational Time Dilation

When using special relativity's relativistic Doppler relationships to calculate the change in energy and frequency (assuming no complicating route-dependent effects such as those caused by the frame-dragging of rotating black holes), then the Gravitational redshift and blueshift frequency ratios are the inverse of each other, suggesting that the "seen" frequency-change corresponds to the actual difference in underlying clockrate. Route-dependence due to frame-dragging may come into play, which would invalidate this idea and complicate the process of determining globally-agreed differences in underlying clock rate. For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... In physics, the relativistic Doppler effect is change in the observed frequency of light due to the relative motion of source and observer when taking into account the Special Theory of Relativity. ... This article is in need of attention from an expert on the subject. ... According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ... A rotating black hole (Kerr black hole or Kerr-Newman black hole) is a black hole that possesses angular momentum. ... Blue shift is the opposite of redshift, the latter being much more noted due to its importance to modern astronomy. ... Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ... According to Albert Einsteins theory of general relativity, space and time get pulled out of shape near a rotating body in a phenomenon referred to as frame-dragging. ...

While gravitational redshift refers to what is seen, gravitational time dilation refers to what is deduced to be "really" happening once observational effects are taken into account. Gravitational time dilation is a consequence of Albert Einsteins theories of relativity and related theories which causes time to pass at different rates in regions of a different gravitational potential; the higher the local distortion of spacetime due to gravity, the slower time passes. ...

Primary sources

• John Michell "On the means of discovering the distance, magnitude etc. of the fixed stars ..." Philosophical Transactions of the Royal Society (1784) 35-57, & Tab III

• Albert Einstein, "The effect of gravity on light" (1911)

• Albert Einstein, "Relativity: the Special and General Theory." (@Project Gutenberg).

• R.V. Pound and G.A. Rebka, Jr. "Gravitational Red-Shift in Nuclear Resonance" Phys. Rev. Lett. 3 439-441 (1959)

• R.V. Pound and J.L. Snider "Effect of gravity on gamma radiation" Phys. Rev. 140 B 788-803 (1965)

• R.V. Pound, "Weighing Photons" Classical and Quantum Gravity 17 2303-2311 (2000)

See also:

• Tests of general relativity
• Equivalence principle
• Gravitational time dilation
• redshift