Abstract
In 1919, Sir Arthur Eddington conducted an experiment during a total solar eclipse to test a key prediction of Albert Einstein’s theory of general relativity. Einstein predicted that light from stars passing near the Sun would be bent due to the Sun’s gravitational field. Eddington’s experiment measured the apparent position of stars near the Sun’s edge, and the results supported Einstein’s prediction, marking a major milestone in the acceptance of general relativity and transforming Einstein into an international figure in science.
Introduction
Einstein’s theory of general relativity, introduced in 1915, suggested that massive objects, such as the Sun, cause curvature in spacetime, resulting in the bending of light. This was a stark departure from Newtonian physics, which did not account for gravitational effects on light. One of the critical predictions of general relativity was that starlight passing close to the Sun would bend by a specific angle. Testing this prediction required observations during a solar eclipse when the Sun’s light would be blocked, allowing stars near the Sun to be visible.
Experiment Details
Eddington and his team planned the 1919 eclipse experiment to measure the apparent positions of stars in the vicinity of the Sun during the eclipse. Two expeditions were organized: one to the island of Príncipe off the west coast of Africa and another to Sobral in Brazil. During the eclipse, the positions of stars were photographed, and these positions were compared with images taken when the Sun was not near those stars. The goal was to measure the angular displacement caused by the Sun’s gravitational influence on the starlight.
The key equipment included telescopes mounted with photographic plates. The positions of stars were recorded during the eclipse and later compared to their “normal” positions (observed when the Sun was not in the field of view) to detect any shift.
Results and Significance
The results from both locations confirmed that the starlight was indeed bent as it passed near the Sun, with an angular deflection close to 1.75 arcseconds—precisely what general relativity predicted. This finding was in contrast to Newtonian physics, which predicted only about half of this value. Eddington’s results were heralded as a triumph for Einstein’s theory, solidifying general relativity as a major advancement in physics and reshaping our understanding of gravity, spacetime, and the universe.
Follow-on Experiments
In the years following Eddington’s experiment, other eclipse observations and more advanced techniques, such as radio wave deflection measurements from distant galaxies, have been used to confirm the predictions of general relativity with greater accuracy. Modern space telescopes and radio interferometry have also contributed to more precise measurements of gravitational lensing, providing further confirmation of Einstein’s theory.
Conclusion
Eddington’s 1919 experiment was pivotal in validating Einstein’s theory of general relativity. By providing direct evidence of the bending of light by gravity, the experiment not only confirmed a critical prediction but also helped shift the scientific consensus away from Newtonian gravity. The success of the experiment marked a new era in physics and remains a cornerstone in the history of general relativity. Subsequent experiments have only reinforced Eddington’s findings, ensuring the theory’s lasting significance in both theoretical and observational physics.