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29 May 2019

Arthur Eddington, the Man Who Invented Einstein

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A poll by the journal Physics World exalted Albert Einstein as the greatest physicist in history. But it is clear that German scientist is much more. It would really be necessary to have grown up in a deep cave not to recognize both his name and his classic image. However, beyond the immense value of his contributions to science, the fact that he has become an icon of popular culture is mainly due to a story that happened one hundred years ago, on May 29, 1919, whose main protagonist was the British astronomer Arthur Eddington.

In the second decade of the last century, Einstein had already achieved all the renown and recognition among his colleagues that any scientist could dream of. He would still have to wait until 1921 to receive the Nobel Prize, but from the beginning of the decade he was already a recurring name in the Nobel nominations. His great reputation was forged in 1905, which today is considered the annus mirabilis or miraculous year in the history of the German, when he published revolutionary papers on four topics: Brownian motion, the photoelectric effect, special relativity and the equivalence between mass and energy through the most famous equation in history: E = mc2.

But at that time, Einstein was nothing more than a highly prestigious scientist, like so many others. His leap to immortality began to take shape in 1911, when he was working on the generalisation of relativity to gravitational fields to build a theory of gravity that modified that of Newton. That year he published a study entitled “Über den Einfluß der Schwerkraft auf die Ausbreitung des Lichtes“, or “On the influence of gravitation on the propagation of light”. In this work he predicted that great masses were able to bend light. In fact, the effect was already suggested in Newton’s work, but Newton could not explain the enigma of gravity’s action at a distance. A few years later, Einstein would calculate a curvature twice as large as that predicted by Newtonian calculations.

A challenge to corroborate Einstein

Shortly thereafter, one of Einstein’s collaborators, the German astronomer Erwin Finlay-Freundlich, challenged his colleagues: if Einstein’s model was correct, it should be possible to detect the deflection of the starlight that reaches us after skimming past the enormous mass of the Sun. But since the intense light of the Sun blinds us to the glimmer of the stars, this could only be done during an eclipse, when the occultation of the Sun by the Moon would make it possible to make out the twinkling stars in the sky. If Einstein was right, the stars would appear in the sky slightly displaced from their expected position.

Portrait of Arthur Stanley Eddington. Source: Wikimedia

Finlay-Freundlich himself attempted to verify this prediction by taking advantage of a solar eclipse in 1914, but the outbreak of World War I prevented it. Fortunately, he was not alone in his endeavour. “Eddington had become the main supporter of Einstein’s general theory of relativity in the UK as soon as he read Einstein’s work, which had to be smuggled out of Germany via neutral Netherlands during WWI,” explains Ron Cowen, author of Gravity’s Century: From Einstein’s Eclipse to Images of Black Holes (Harvard University Press, 2019), to OpenMind.

Expeditions to photograph the eclipse

Eddington dedicated himself to promoting and publicising Einstein’s work among his colleagues. However, he was not satisfied with just this: the astronomer was also determined to test the prediction about the curvature of light. “Frank Dyson, the UK’s Astronomer Royal, realised that the 1919 solar eclipse would be a perfect time to test Einstein’s theory,” says Cowen. The eclipse of that year, adds the author, was not only going to be one of the longest of the 20th century, but the Sun would also be located near a very large group of stars.

In view of all this, Dyson proposed sending expeditions to photograph the eclipse from two places where it could be observed in its entirety. Eddington also had a personal reason to embark on the project. “As a lifelong Quaker, Eddington abhorred the war and saw the eclipse expedition, in which British astronomers would test the theory of a German-born scientist, just after World War I, as a way to heal the wounds of the war,” says Cowen.

Image of the 1919 eclipse. Credit: F. W. Dyson, A. S. Eddington, and C. Davidson

Eddington and Edwin Cottingham left for the island of Príncipe, on the west coast of Africa, while Andrew Crommelin and Charles Davidson travelled to Sobral, in Brazil. The double coverage of the eclipse increased the chances of enjoying a clear sky to photograph the phenomenon. Although bad weather on May 29 threatened the success of Eddington and Cottingham, in the end both expeditions managed to capture images.

The end of the Newtonian model

The results were presented in an atmosphere of great expectation at a joint meeting of the Royal Society and the Royal Astronomical Society held on November 6 of that year. The verdict was unequivocal: Einstein was right. But the implications of that discovery reached infinitely beyond an interesting astronomical phenomenon; the verification of a consequence of general relativity meant validating Einstein’s theory of gravity, overthrowing the Newtonian model that had remained in force for more than 230 years and unveiling the enigma of action at a distance: according to Einstein, the universe is formed by a fabric of space-time that is distorted by the mass of bodies, and this distortion also bends light.

Instruments to observe the eclipse in Sobral (1919). Credit: C. Davidson

Therefore, the impact of that finding was immensely profound, and the press knew just how to give it the right resonance. The day after the meeting, the front page of the Times of London published a headline with three columns: “Revolution in science: new theory of the universe: Newtonian ideas overthrown”. The newspaper quoted the then president of the Royal Society, physicist Joseph John Thomson, for whom Einstein’s theory was “One of the most momentous, if not the most momentous, pronouncements of human thought.” On the other side of the Atlantic, the New York Times echoed the sentiment on November 10, also on its front page, with the headline “Light all askew in the heavens: Einstein’s theory triumphs”.

“The news set off a chain reaction around the globe,” says Cowen. “Overnight, Einstein had become the first science superstar.” Interestingly, it was that media commotion that elevated Einstein to the status of an idol, rather than his own theory, which at the time not even many physicists could fully understand. According to the article in the Times that sowed the seed of the Einstein frenzy, Thomson himself, to whom the discovery of the electron is attributed, “had to confess that no one had really yet succeeded in stating in clear language just what Einstein’s theory is.” “Some said Eddington was one of the few people to understand the theory, perhaps the only one, in the UK,” Cowen concludes.

Javier Yanes

@yanes68

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