Download to read offline
Uploaded byPeter Coles
Revolution in the Skies: The Experiment that made Einstein famous
1) In 1919, expeditions led by Eddington to Principe and Crommelin to Sobral measured the bending of starlight by the Sun during a solar eclipse to test Einstein's theory of general relativity, which predicted light bending would be twice that of Newton's prediction. 2) The measurements found light bending of 1.61 ± 0.40 seconds of arc in Principe and 1.98 ± 0.16 seconds of arc in Sobral, consistent with Einstein's prediction of 1.74 seconds of arc. 3) This confirmed Einstein's theory of general relativity and made him famous worldwide, revolutionizing our understanding of space, time, gravity and the universe.
More Related Content
Similar to Revolution in the Skies: The Experiment that made Einstein famous
More from Peter Coles
Revolution in the Skies: The Experiment that made Einstein famous
- 1. `Revolution in theSkies’ The Story of the 1919 Eclipse Expeditions Peter Coles Department of Theoretical Physics
- 4. Newton’s Laws ofMotion • I. Every body continues in a state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed upon it. • II. Rate of change of momentum is proportional to the impressed force, and is in the direction in which this force acts • III. To every action, there is always opposed an equal reaction.
- 5. “..the Supreme Godis a Being eternal, infinite, absolutely perfect…He endures forever and is everywhere present; and by existing always and everywhere, he constitutes duration and space..” Newton, Principia (General Scholium). Absolute Space, Absolute Time
- 6. Universal Gravitation • “theattractive force between any two bodies depends on the product of the masses of the bodies and on the square of the distance between them” • “the attraction always is in a duplicate proportion to the Distance from the Center Reciprocall”
- 7. The Mystery ofMass • Mass can represent the resistance of a body to being accelerated (inertial) • ..or the strength of gravity produced (active) • ..or the tendency to feel gravity (passive) • Are these masses the same?
- 8. The Principle ofEquivalence maF 2 r GMm F Why should these masses be the same? Perhaps this Equivalence is because of a some sort of Principle?
- 10. The Einstein (R)evolution •Albert Einstein was born in Ulm on 14 March 1879 • After failing the entrance exam the previous year, he entered the Institute of Technology (Zurich) in 1896. • “Too lazy” to continue as a scientist, he left in 1902 to become a patent clerk in Bern. • In 1905, he revolutionized science with the special theory of relativity. “E=mc2” and all that. • In 1915, he went even further, with the general theory of relativity.
- 11. General Relativity • The“Principle of Equivalence” • Acceleration and Gravity • The curving of space • ..and the bending of light!
- 15. Light Bending..a comedyof errors. • Newton 1704 “Do not Bodies act upon Light at a distance, and by their action bend its Rays?” • 1802 Johann Georg von Soldner, calculates bending of light by the Sun: 0.87 seconds of arc • 1907 Einstein thinks about light bending, but then shelves the idea. • 1911 Einstein tries again using “E=mc2”; gets Soldner’s answer: 0.87 seconds of arc. • 1915 Einstein tries again, and finds a mistake - a factor of two. The new value is 1.74 seconds of arc.
- 17. The Factor Two 222222 drdrdtcds 222 1 2 22 2 2 2 1 2 1 drdr rc GM dtc rc GM ds Flat Space: Schwarzschild: Energy Momentum
- 18. Eddington and theExpeditions • Arthur Stanley Eddington was born in 1882. • In 1912 becomes Plumian Professor of Astronomy and Experimental Philosophy at Cambridge. • Earlier in 1912 Eddington had been involved in an Eclipse expedition to Argentina. It rained. • 1916 de Sitter tells him about Einstein’s prediction and suggests the idea of light bending measurements during an eclipse. • 1917, Frank Watson Dyson, the Astronomer Royal realises the eclipse of 29 May 1919 would be perfect.
- 20. The Eclipse of1919 • Date: 29 May 1919 • Path of Totality is across the South Atlantic from Sobral to Principe • Duration is long…7 minutes or so at Principe. • Near the Sun during totality was not just one star, but a cluster of stars: The Hyades
- 22. War and Peace •BUT Eddington was a Quaker, and therefore a pacifist. • The First World War had started in 1914, but conscription was not introduced in the British Army until 1916. • Eddington refused to be drafted… • He was saved by a deal by Dyson, which protected him on condition he agreed to lead an expedition in 1919 if the war was over.
- 23. The Equipment • Funding:£100 for equipment, £1000 for travel and labour costs • Two “astrographic” object glasses, one to Principe (Oxford), Sobral (Greenwich), both stopped down to 8 inches. • A 4 inch telescope taken to Sobral as a backup • All were equipped with coelostats • The two astrographic object glasses were mounted in stainless steel tubes
- 25. The Irish Connection •All the optical equipment was made by Grubb in Dublin. • The Oxford astrographic moved to Keele University in 1962 • The RGO moved to Herstmonceux • The 4-inch telescope and coelostat are on display at Dunsink Observatory
- 32. Some Data Analysis… DyEfeydx DxEcbyax y x Coordinatesof stars Measured deflections Gravitational deflections at star positions
- 33. The Results • Eddingtonwent to Principe, off the coast of (then) Spanish Guinea • Crommelin went to Sobral (Northern Brazil). • Eddington was nearly rained out “THROUGH CLOUD. HOPEFUL” • Crommelin was luckier “ECLIPSE SPLENDID” • In the end Eddington got 1.610.40 seconds, Crommelin 1.980.16 • After some controversy, Einstein was declared the winner!
- 35. The Controversy • Principeastrographic: 2 “poor” plates. ( =1.62 ± 0.45) • Sobral astrographic: 18 “poor” plates ( = 0.86 ± 0.48) • Sobral 4”: 8 “good” plates: ( = 1.98 ± 0.18) • Eddington included the Principe results, despite not really getting enough measurements for an astrometric solution • The Sobral astrographic suffered from serious optical problems but plates were remeasured in 1979: =1.55 ± 0.34
- 37. The Aftermath • Thismade Einstein more famous than any scientist before or since. • Reconciliation of Britain and Germany • What might have been…the two expeditions of 1912 and 1914 failed to take measurements when the prediction was wrong! • Much better measurements were made in 1922, and later using radio observations.
- 38. Curiosities • Einstein becamethe most famous scientist ever - it was not 1905, but 1919, that made Einstein a household name. • What would have happened if the measurement had been made when Einstein had the wrong answer?