Arthur Stanley Eddington

English astrophysicist

• Born: December 28, 1882; Kendal, England
• Died: November 22, 1944; Cambridge, England

Twentieth-century English astrophysicist Arthur Stanley Eddington was knighted in 1930 for his foundational contributions to astrophysics—particularly our understanding of the structure of stars—and for his work assisting Albert Einstein with his theory of general relativity.

Primary fields: Astronomy; physics; mathematics

Specialties: Astrophysics; relativity

Early Life

Arthur Stanley Eddington was born on December 28, 1882, in Kendal, England, to Arthur Henry and Sarah Ann Shout Eddington. His father died of typhoid two years later, so Stanley moved with his mother and sister, Winifred, to live with his paternal grandmother in Weston-super-Mare, Somerset.

Even when very young, Stanley showed a facility with numbers, a powerful memory, and a fascination in the stars. He had memorized multiplication tables up to 24 × 24 before he even learned to read. At age ten, he was loaned a three-inch telescope, and his passion for observational astronomy blossomed. He would give lectures on astronomical matters to the household servant.

He attended the Brynmelyn School in Weston, where he furthered his academic and athletic ambitions, playing on cricket and soccer teams, and in 1898 at the age of sixteen, he was awarded a scholarship to attend Victoria University (now Manchester University). By his second year, he was top of his class in Latin, English history, mathematics, and mechanics. By the age of nineteen, he had earned a bachelor’s degree in physics and entered Trinity College, Cambridge.

Cambridge University at the time was a worldwide center for mathematics. It was not at all unusual for students to arrive there with years spent at “lesser” schools. The mathematics exams, called the Tripos, were so competitive and difficult that students would hire coaches and train for the exams like Olympic athletes. The top performers were part of an elite group known as wranglers. Eddington was the first person in history to become the senior (first) wrangler after only two years, taking the Tripos and this ultimate honor in 1904.

In 1906, Eddington was appointed chief assistant to the astronomer royal at Royal Greenwich Observatory. A year later, he won a fellowship at Trinity College, Cambridge. In 1913, he was given the post of Plumian Professor of Astronomy and Experimental Philosophy at Cambridge and, by 1914, the thirty-two-year-old Eddington had become the director of the Cambridge Observatory.

Life’s Work

The main thrust of Eddington’s work in the first half of his life focused on stars. By his time, stars were understood as balls of gas. However, it was thought that the internal thermal pressure within stars was enough to counterbalance the effects of gravity and prevent collapse. Eddington demonstrated that this was not so and that there must be outward pressure exerted by the electromagnetic radiation produced inside stars to keep them from collapsing. He also determined that the ionized state of matter (plasma) in stars allows it to be compressed to densities far in excess of a solid.

Eddington was prone to making bold theoretical leaps, based on his extreme facility with and faith in mathematics. By his calculations, he predicted that stars require a source of nuclear energy, even predicting hydrogen as the most likely fuel, some fifteen years before nuclear reactions were discovered.

In parallel to his work on astrophysics, Eddington contributed greatly to the development of the general theory of relativity. Almost immediately after the publication of Einstein’s theory in 1915, Eddington grasped its significance and became the English voice of relativity. His status as its proponent was cemented with the publication of two popular books on relativity, Space, Time and Gravitation (1920) and Mathematical Theory of Relativity (1923).

His ultimate contribution to relativity, undoubtedly, occurred in May 1919. Relativity, to this point, was lacking in any observational evidence. Eddington led an expedition to the island of Príncipe, off the west coast of Africa, to photograph a total solar eclipse. One prediction of relativity is that light can be bent by sufficient gravity, and the sun is just the sort of object to provide enough gravity to bend light by a measurable amount. The sun, however, also produces so much light of its own that it makes it difficult to measure the light from stars around it.

By photographing the eclipse, Eddington was able to capture the apparent positions of stars around the sun that would normally be invisible if not for the moon blocking the sun’s rays. By comparing their apparent position in the eclipse to where they would, based on previous observations, be expected to be, Eddington was able to provide evidence that the sun’s gravity had bent the rays of light traveling from distant stars to the Earth. There has since been much discussion over whether Eddington’s experiment was corrupted by confirmation bias.

In 1924, Eddington pinned down the mass-luminosity relationship for stars. In essence, he determined that there is a strong and direct relationship between a star’s mass and its luminosity, or brightness—the higher the mass, the higher the luminosity. By 1926, Eddington’s work on the composition of stars had matured, and his book The Internal Constitution of the Stars(1926) collected much of what he had done.

Later in his life, Eddington’s efforts took on a tinge of mysticism. He had always been a devout Quaker and unflappable idealist, but in his later years, he became fixated on attempts to bring together everything known at the time about quantum theory, relativity, cosmology, and gravitation. He called this project “Fundamental Theory.” Eddington was obsessed with dimensionless fundamental constants. He went so far as to claim that he had found a basis for all of physics in algebra and that he had calculated the exact number of protons in the universe. (This number, known as the Eddington number, was not taken very seriously at its time and is not accepted today.)

Eddington died in Cambridge in 1944 and was buried in the Parish of the Ascension Burial Ground in Cambridge. He never completed his work on fundamental theory before his death, but his book on the matter, Fundamental Theory, was published after his death, in 1946.

Impact

Eddington’s work was foundational to astrophysics’ understanding of the structure of stars. His extreme skill in mathematics, coupled with his interest in astronomy,led him to father the field of theoretical astrophysics. He, for instance, devised an equation for radiation equilibrium in stars that was used in nearly all stellar structure calculations thereafter. His 1926 book, The Internal Constitution of the Stars, collected his mature work on stellar structure and remained a vital text in the field of astrophysics for decades after its publication.

Eddington is most famous, however, for his connection to Albert Einstein and relativity. He was the chief proponent and popularizer of the new theory in England, and his 1919 expedition is still—despite concerns over confirmation bias—touted as the first empirical evidence for Einstein’s theory. Knowing and understanding Eddington’s importance to the development of relativity is essential in combating the popular myth that the relativity theory emerged, fully formed and proven, from Einstein’s head.

In keeping with his Quaker beliefs, Eddington was a paragon of scientific cooperation in a world that saw itself embroiled in two global conflicts. Beyond his important contributions to basic science, Eddington’s life and work highlighted the interplay between science and society that has shaped history.

Bibliography

Eddington, Arthur Stanley. Space, Time and Gravitation: An Outline of the General Relativity Theory. Cambridge: Cambridge UP, 1920. Print. Eddington’s major book popularizing relativity theory. Provides insight into Eddington’s intellect and his importance to the dissemination of relativity theory.

Kennefick, Daniel. “Testing Relativity from the 1919 Eclipse—A Question of Bias.” Physics Today 62.3 (2009): 37–42. Print. Focuses on the doubts that have arisen since the 1919 expedition as to whether confirmation bias may have entered into Eddington’s findings. Also tracks the development of scientific opinion (new analysis, modern interpretations) with regard to Eddington’s seminal work.

Stanley, Matthew. “‘An Expedition to Heal the Wounds of War’: The 1919 Eclipse and Eddington as Quaker Adventurer.” Isis 94.1 (2003): 57–89. Print. Places Eddington’s 1919 expedition into social, political, and religious contexts and offers a record of the expedition.

---. Practical Mystic: Religion, Science, and A. S. Eddington. Chicago: U of Chicago P, 2007. Print. An examination of the intersection between Eddington’s lifelong Quaker faith and his work as a scientist.