Eddington experiment
The Eddington experiment was an observational test of
Background
One of the first considerations of gravitational deflection of light was published in 1801, when
In October 1911, responding to Einstein's encouragement, German astronomer
In 1914 three eclipse expeditions, from Argentina, Germany, and the US, were committed to testing Einstein's theory by observing for light deflection. The three directors were
A second attempt by American astronomers to measure the effect during the 1918 eclipse was foiled by clouds in one location[7] and by ambiguous results due to the lack of the correct equipment in another.[1][8]
Einstein's 1911 paper predicted deflection of star light on the limb of the Sun to be 0.83 seconds of arc and encouraged astronomers to test this prediction by observing stars near the Sun during a solar eclipse.[9] It is fortunate for Einstein that the weather precluded results by Perrine in 1912 and Perrine, Freundlich, and Campbell in 1914. If results had been obtained they may have disproved the 1911 prediction setting back Einstein's reputation. In any case, Einstein corrected his prediction in his 1915 paper on General Relativity to 1.75 seconds of arc for a star on the limb. Einstein and subsequent astronomers both benefitted from this correction.[10]
Eddington's interest in general relativity began in 1916, during
Wartime conscription in Britain was introduced in 1917. At the age of 34, Eddington was eligible to be drafted into the military, but his exemption from this was obtained by his university on the grounds of national interest. This exemption was later appealed by the War Ministry, and at a series of hearings in June and July 1918, Eddington, who was a
Theory
The theory behind the experiment concerns the predicted 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 approximate angular deflection δφ for a massless particle coming in from infinity and going back out to infinity is given by the following formula:[b]
Here, b can be interpreted as the distance of closest approach. Although this formula is approximate, it is accurate for most measurements of
Expeditions and observations
The aim of the expeditions was to take advantage of the shielding effect of the Moon during a total solar eclipse, and to use astrometry to measure the positions of the stars in the sky around the Sun during the eclipse. These stars, not normally visible in the daytime due to the brightness of the Sun, would become visible during the moment of totality when the Moon covered the solar disc. A difference in the observed position of the stars during the eclipse, compared to their normal position (measured some months earlier at night, when the Sun is not in the field of view), would indicate that the light from these stars had bent as it passed close to the Sun. Dyson, when planning the expedition in 1916, had chosen the 1919 eclipse because it would take place with the Sun in front of a bright group of stars called the Hyades. The brightness of these stars would make it easier to measure any changes in position.
Two teams of two people were to be sent to make observations of the eclipse at two locations: the West African island of Príncipe and the Brazilian town of Sobral.
The Príncipe expedition members were Eddington and Edwin Turner Cottingham, from the
The expeditions were organised by the Joint Permanent Eclipse Committee, a joint committee between the Royal Society and the Royal Astronomical Society, chaired by Dyson, the Astronomer Royal. The funding application for the expedition was made to the Government Grant Committee, asking for £100 for instruments and £1000 for travel and other costs.
Sobral
In mid-1918, researchers from the Brazilian National Observatory, determined that the city of Sobral, Ceará, was the best geographical position to observe the Solar Eclipse. Its director, Henrique Charles Morize , sent a report to worldwide scientific institutions on the subject, including the Royal Astronomical Society, London.[13]
The
The gear was made by two astrographic telescopes coupled to mirror systems known as coelostats; a main telescope from the
At April 30 the team arrived at Sobral. The eclipse day started cloudy, but the sky cleared and the Moon's disk began to obscure the Sun shortly before 8:56 am, and the eclipse lasted 5m13s. The team remained at Sobral until July, to photograph the same star field at night.[13][15]
The main telescope recorded twelve stars, while the backup one recorded seven. The main telescope had blurred images, which were discarded from the final conclusion, while the smaller one had the clearest images and was the most trustworthy.[13][14][15] Daniel Kennefick defends that without the Sobral photographs, the results of the 1919 eclipse would have been inconclusive and that the expeditions during future eclipses failed to improve the data.[14]
The British team was joined by the Brazilian team led by Henrique Charles Morize and the astronomers Lélio Gama , Domingos Fernandes da Costa, Allyrio Hugueney de Mattos and Teófilo Lee with the objective of producing spectroscopic observations of the Sun’s corona.[16]
The team set its gear at a plaza in front of the church of Patrocínio, where today is the Eclipse Museum. The team took several 24 by 18 and 9 by 12 cm plates capturing the Sun and the stars' positions near its edge, but unfortunately, no meaningful conclusions were drawn from the data produced by the Brazilian team, and its contribution was defined as just logistical support for the British team and climate observations.[16] Its plates were restored by the National Observatory in 2015,[16] while the British team plates were lost after 1979.[14]
The third expedition from that day was formed by Daniel Maynard Wise and Andrew Thomson, from the Carnegie Institution. Their goal was to study the eclipse effects on the magnetic field and atmospheric electricity.[16]
In 1925, Einstein stated to the Brazilian press about the results: "The problem conceived by my brain was solved by the bright Brazilian sky".[15][17]
Príncipe
The equipment used for the Príncipe expedition was an astrographic lens borrowed from the Radcliffe Observatory in Oxford. Eddington sailed from England in March 1919. By mid-May he had his equipment set up on Príncipe, an island in the Gulf of Guinea off the coast of West Africa, near what was then Spanish Guinea. The eclipse was due to take place in the early afternoon of 29 May, at 2pm, but that morning there was a storm with heavy rain. Eddington wrote:
The rain stopped about noon and about 1.30 ... we began to get a glimpse of the sun. We had to carry out our photographs in faith. I did not see the eclipse, being too busy changing plates, except for one glance to make sure that it had begun and another half-way through to see how much cloud there was. We took sixteen photographs. They are all good of the sun, showing a very remarkable prominence; but the cloud has interfered with the star images. The last few photographs show a few images which I hope will give us what we need ...
Eddington developed the photographs on Príncipe, and attempted to measure the change in the stellar positions during the eclipse. On 3 June, despite the clouds that had reduced the quality of the plates, Eddington recorded in his notebook: "... one plate I measured gave a result agreeing with Einstein."
British future astronomer and astrophysicist Cecilia Payne-Gaposchkin attended the expedition and Eddington's lecture and later related how strongly the voyage had affected her.[18]
Results and publication
The results were announced at a meeting of the Royal Society in November 1919,[19] and published in the Philosophical Transactions of the Royal Society in 1920.[2] Following the return of the expedition, Eddington was addressing a dinner held by the Royal Astronomical Society, and, showing his more light-hearted side, recited the following verse that he had composed in a style parodying the Rubaiyat of Omar Khayyam:[20]
Oh leave the Wise our measures to collate
One thing at least is certain, light has weight
One thing is certain and the rest debate
Light rays, when near the Sun, do not go straight.—Arthur Stanley Eddington, RAS dinner[21]
Later replications
The light deflection measurements were repeated by expeditions that observed the total solar eclipse of 21 September 1922 in Australia. An important role in this was played by the Lick Observatory[c] and the Mount Wilson Observatory, both in California, USA.[8] On April 12, 1923, William Wallace Campbell announced that the preliminary new results confirmed Einstein’s theory of relativity and prediction of the amount of light deflection with measurements from over 200 stars.[23] Final results published in 1928 used measurements of over 3,000 star images.[24]
Reception
The presentation of the results at the joint November 6, 1919 session of Royal Society and Royal Astronomical Society led to intensive press coverage first in Great Britain and a few days later in the US press, notably in The New York Times, and some days later still in the German press. While Einstein had been a moderately famous public figure in Germany for a few years by that time, the articles in question marked the beginning of his international celebrity status.[25] A notable exception was Belgium, where the Eddington results were given the cold shoulder – partly because Einstein was seen as representing Germany, with the suffering of Belgium in World War I still very present in the country.[26] The sudden popularity of Einstein's theories led to an "Einstein boom" of popular science books.[27]
While there is a later anecdote describing Einstein as unimpressed about the experimental results, and sure of his theory even in the absence of evidence (stating, when asked what he would have said if the results had been otherwise, "Then I would feel sorry for the dear Lord. The theory is correct anyway."[28]) the evidence of Einstein's letters to other scientists indicates, on the contrary, that he was both impressed and moved by the new results, and regarded them as an important success.[29]
The 1919 results were also used as part of the systematic efforts by the Nobel laureate Philipp Lenard to discredit Einstein, whom Lenard, himself an avid national socialist and exponent of what he saw as "German physics," saw as a dangerous exponent of unnatural "Jewish physics".[30] Lenard pointed to the 1801 prediction that Johann Georg von Soldner had derived from Newtonian gravity for starlight bending around a massive object,[31] which corresponds to half the general-relativistic prediction derived by Einstein in 1915, and thus to Einstein's own earlier derivation of 1911, and claimed that it proved Einstein to be a plagiarist, and that von Soldner deserved to be given credit for the 1919 result.
Both the 1919 results themselves and Eddington's text book on general relativity, whose second edition including the results saw numerous translations as interest in Einstein's theory grew, played important roles in the reception of Einstein's theory in the scientific community.[32] It is notable that while the Eddington results were seen as a confirmation of Einstein's prediction, and in that capacity soon found their way into general relativity text books,[33] among observers followed a decade-long discussion of the quantitative values of light deflection, with the precise results in contention even after several expeditions had repeated Eddington's observations on the occasion of subsequent eclipses.[34] The discussion concerned both the data analysis – such as the different weight assigned to different stars in the 1922 and 1929 eclipse expeditions – and the question of specific systematic effects that could skew the results.[35][36]
All in all, eclipse measurements of this kind, using visible light, retained considerable uncertainty, and it was only radio-astronomical measurements in the late 1960s that definitively showed that the amount of deflection was the full value predicted by general relativity, and not half that number as predicted by a "Newtonian" calculation.
At about the time of the last serious photo-plate eclipse measurements, by a University of Texas expedition observing in Mauritania in 1973, doubts began to surface about whether or not the original Eddington measurements were sufficient to vindicate Einstein's prediction, or whether biased analysis by Eddington and his colleagues had skewed the results.
In popular culture
The experiment was central to the plot of the 2008 BBC television film Einstein and Eddington, with David Tennant in the role of Eddington.
See also
Notes
- ^ Following the eclipse expedition in 1919, Eddington published Space Time and Gravitation (1920), and his university lectures would form the basis for his magnum opus on the subject, Mathematical Theory of Relativity (1923), said by Einstein to be "... the finest presentation of the subject in any language".[11]
- ^ For the derivation of this formula, see the article on the Two-body problem in general relativity.
- ^ For a historical review emphasizing the role of the Lick team in the confirmation of light's bending, see Jeffrey Crelisnsten's 1983 article in Historical Studies in the Physical Sciences.[22]
References
- ^ JSTOR 27757471.
- ^ .
- ^ . Retrieved 2 November 2021.
- ^ Gates & Pelletier (2019), p. 52.
- ^ Gates & Pelletier (2019).
- S2CID 120712519.
- Bibcode:1918PA.....26R.447W.
- ^ a b Burgess, A. (11 August 2017). "The 1922 Eclipse Adventure That Sought to Confirm the Theory of Relativity", Atlas Obscura. Retrieved 2 November 2020.
- .
- ^ Gates & Pelletier (2019), pp. 120–121.
- ISSN 0035-872X.
- ^
Stanley, Matthew (2003). "'An Expedition to Heal the Wounds of War': The 1919 Eclipse and Eddington as Quaker Adventurer". Isis. 94 (1): 57–89. S2CID 25615643.
- ^ a b c d e Pivetta, Marcos; Andrade, Rodrigo de Oliveira (December 2019). "When light bent". revistapesquisa.fapesp.br. Retrieved 11 April 2023.
- ^ a b c d "Daniel Kennefick: The importance of Sobral". revistapesquisa.fapesp.br. December 2019. Retrieved 11 April 2023.
- ^ S2CID 202138019. Retrieved 11 April 2023.
- ^ a b c d Andrade, Rodrigo de Oliveira (December 2019). "In the British expedition's shadow". revistapesquisa.fapesp.br. Retrieved 11 April 2023.
- ^ "O céo do Brasil". O Jornal (in Brazilian Portuguese). Vol. VII, no. 1918. 22 March 1925. p. 2. Retrieved 11 April 2023.
- ISSN 1366-8781.
- ^ McKie, Robin (12 May 2019). "100 years on: The pictures that changed our view of the universe". The Observer. Guardian Media Group. Retrieved 27 September 2019.
- ^ O'Connor, J. J.; Robertson, E. F. (October 2003), "Arthur Eddington - Biography", The MacTutor History of Mathematics, School of Mathematics and Statistics, University of St Andrews, retrieved 27 May 2019
- ^ Douglas, A. V. (1956). The Life of Arthur Stanley Eddington.
- JSTOR 27757525.
- S2CID 117968484.
- S2CID 122860175.
- ISBN 978-3518404898.
- ^ Sjang ten Hagen (10 October 2016). "The Belgian reception of relativity theory". Shells and Pebbles Blog. Retrieved 21 September 2022.
- ISBN 978-0-7546-5850-4.
- ISBN 9780814316504.
- . See: Section 7
- ^ Ball, Philip (13 February 2015). "How 2 Pro-Nazi Nobelists Attacked Einstein's 'Jewish Science'". Scientific American. [Excerpt]. Retrieved 30 January 2021.
- .
- ISBN 978-94-009-3875-5.
- ^ Notably:
- Weyl, Hermann (1921). Raum, Zeit, Materie (4th extended ed.). Springer. p. 223. and
- Eddington, Arthur S. (1921). "Chapter 7". Space, Time and Gravitation. Cambridge University Press.
- ISBN 978-3-0348-9967-3.
- .
- ^ Kennefick (2019), Ch. 13; Ch.14.
- S2CID 1385516.
- ^ Kennefick (2019), p. 214.
- JSTOR 27757471.
- ^ Collins & Pinch (1993).
- S2CID 120524925.
Sources and further reading
- Gates, Sylvester J. Jr; Pelletier, Cathie (2019). Proving Einstein right: The daring expeditions that changed how we look at the universe (First ed.). New York: PublicAffairs. ISBN 978-1541762251.
- Kennefick, Daniel (2019). No Shadow of a Doubt: The 1919 Eclipse That Confirmed Einstein's Theory of Relativity. Princeton: Princeton University Press. ISBN 9780691183862.
- ISBN 0521477360.
- Cowen, Ron (May 2019). Gravity's Century: From Einstein's Eclipse to Images of Black Holes (Illustrated ed.). Harvard University Press. ISBN 978-0-674-97496-8.
- Crelinsten, Jeffrey (May 2006). Einstein's Jury: The Race to Test Relativity. Princeton University Press. ISBN 978-0-691-12310-3.
- Stanley, Matthew (2019). Einstein's War: How Relativity Triumphed Amid the Vicious Nationalism of World War I. Dutton. ISBN 978-1-5247-4541-7.
External links
- Eclipse 1919, website about the eclipse, the expeditions and centenary events
- "Eddington's Eclipse and Einstein's Celebrity" Discovery (audio) episode (from BBC World Service)
- "The man who made Einstein world-famous" (BBC News, 24 May 2019)
- "Matthew Stanley and Einstein's War". Archived 2020-07-30 at the Wayback Machine (Clarke Center for Human Imagination, UCSD podcast)
- "100 years on: the pictures that changed our view of the universe" (The Observer, 12 May 2019)
- "How the 1919 Solar Eclipse Made Einstein the World's Most Famous Scientist" (Discover magazine, May 2019)
- "A Total Solar Eclipse 100 Years Ago Proved Einstein's General Relativity" (Smithsonian Magazine, 24 May 2019)
- "Einstein, Eddington and the 1919 eclipse" (Nature, April 2019)
- "Arthur S. Eddington: From Physics to Philosophy and Back Again" (Eddington Conference, 27–29 May 2019, Paris)