What happened to the man who verified Einstein's theory? asks Arthur Miller

When Albert Einstein's theory of the cosmos was verified on May 19, 1919, the German physicist became an icon of the 20th century almost overnight. His face became familiar to everyone, his name synonymous with genius. In this Year of Science, we celebrate the centenary of many of Einstein's achievements. Yet Arthur Stanley Eddington, the man who found the crucial evidence for the general theory of relativity and introduced the revolutionary ideas to the English-speaking world, has been virtually forgotten.

In his day, Eddington was known as the world's greatest astrophysicist, and he became renowned for helping usher in the age of relativity. Some years later, he bumped into the German physicist Ludwig Silberstein at a meeting in London.

Silberstein exclaimed in jocular tones: "You must be one of the three people in the world who understand relativity." Eddington enjoyed recounting the exchange that followed. "I said: 'Oh! I don't know,' to which he said: 'Don't be modest, Eddington.' To which I replied: 'On the contrary! I am wondering who the third person is!'"

ÖйúAƬ

The man was an enigma and to add to the mystery, shortly before his death, Eddington destroyed all his personal correspondence. He was born in 1882 into a Quaker family in Kendal in the Lake District. His father, a headmaster, died when Eddington was young, leaving his family in poverty.

Even as a child he was interested in astronomy and studied the night sky through a borrowed telescope. He was fascinated by large numbers and had a prodigious memory. His mother once returned home and asked how he had spent his time. "I've been counting all the words in the Bible," he replied. He succeeded in getting through the Book of Genesis. At night, he counted stars.

ÖйúAƬ

With the help of scholarships, he studied maths and physics at Owens College (which became Manchester University), then went to Trinity College, Cambridge. He was a brilliant and popular student, and colleagues recalled watching with awe as he filled in The Times crossword in the time it took to move his pen across the page. In 1906, Eddington became chief assistant at the Royal Observatory at Greenwich. In 1913, he was appointed Plumian professor of astronomy and experimental philosophy and director of the Cambridge Observatory. Eddington developed the field of modern astrophysics virtually single-handedly and went on to construct the first model of a star, enabling scientists to deduce its temperature, brightness, size and distance based on the light it emitted.

The following year, the world was at war. Across enemy lines in Berlin, a young man called Albert Einstein was turning out paper after paper. A colleague of Eddington's in neutral Holland forwarded some to him. He was gripped. The papers concerned Einstein's general theory of relativity. They were couched in abstruse mathematics, but Eddington immediately grasped their significance. His masterly report on the theory - the first in English - brought it to the attention of many British scientists.

The general theory of relativity was built on Einstein's special theory of relativity, which he had discovered in 1905, his annus mirabilis during which he wrote three papers that changed the course of science. He suggested that light could be represented as a particle as well as a wave; proposed a method to demonstrate that atoms existed; and, in the relativity paper, showed that measurements of space and time depend on the motion of the measuring rods and clocks relative to the laboratory. It also said that space and time were not separate entities but were linked in a space-time continuum.

Einstein's 1905 theory was called "special" because it considered measurements made for motion in a straight line at a constant speed. When he began to look for ways to generalise this to include measurements made in laboratories that were accelerating, he discovered that gravity played a key role. In turn, this revealed a fabric or structure to space-time, through which light travels. Gravity, Einstein concluded, was the effect of matter on space-time, the "well" created by a body, like a depression made in a sheet of rubber by an object resting on it. The deeper the well, the stronger the body's gravity - so the Sun would make a well far deeper than the Earth would because it is so much heavier.

If Einstein was right, light from a distant star that reached us after grazing the surface of the Sun would not travel in a straight line but would be deflected by the severe warping of space-time by the Sun's gravity. If observed from Earth, the star would not appear in its normal position in the sky. A stunning test of the general theory of relativity emerged from this - measure the difference between a star's observed, or apparent, position when it appeared close to the edge of the Sun and its usual one. The British scientific establishment started to make plans to do that. Eddington was at the forefront of the project.

But there was trouble ahead for the brilliant astrophysicist. In 1916, the British Army introduced conscription. Many young scientists were called up.

Many were killed. As a Quaker, Eddington could declare himself a conscientious objector, though it was considered a disgrace when youthful patriots were marching off to fight. At the first hearing on June 14, 1918, to decide whether he might be exempted from the call-up on the basis of his scientific achievements, Eddington did just that. He said he saw no shame in joining his Quaker friends in internment camps in Northern Ireland. The Astronomer Royal then intervened. He proposed that Eddington be exempt but on one condition - that he lead a British scientific team to observe the total eclipse of the Sun on May 29, 1919, to put Einstein's theory to the test. He was granted a year's reprieve to do so.

Soon afterwards, the armistice was signed. But Eddington prepared for the journey nonetheless. It was a huge adventure. Early in March 1919, two expeditions sailed from the UK. One went to Sobral, northeast Brazil. The other, led by Eddington, headed for the tiny Portuguese island of Principe, off the west coast of Africa. By mid-May, the scientists had their instruments in place and took some test photographs. Then disaster struck.

ÖйúAƬ

The eclipse was due at 2pm but that morning the clouds were heavy and the rain poured. The team waited anxiously. "The rain stopped at noon," Eddington recorded, "and about 1.30 we began to get a glimpse of the Sun.

ÖйúAƬ

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 it had begun and another halfway through to see how much cloud there was."

Eddington made the critical micrometer measurements on the best photographs from both Principe and Sobral. To his and everyone's delight, the stars'

normal and apparent positions differed more or less by the amount predicted by the general theory of relativity. Einstein was ecstatic. Eddington wrote to him that "all England is talking about your theory. It has made a tremendous sensation".

In celebration, Eddington penned a small epic in a parody of Edward Fitzgerald's Rub¨¢iy¨¢t of Omar Khayy¨¢m . One verse reads: " And this I know; whether Einstein is right/ Or all his theories are exploded quite,/ One glimpse of stars amid the Darkness caught/ Better than hours of toil by Candle-light ."

Eddington said it was his greatest moment. The New York Times headlined the results: "Stars not where they seem or were calculated to be, but nobody need worry" - for Einstein knew where they were. The war-weary public appreciated the irony that a British scientist had verified a "German theory". Everyone was impressed by photographs of the wild-haired scientist who had divined the laws of the cosmos while looking as if he had witnessed creation itself.

The expedition also made Eddington's name. Throughout the 1920s, he was the world expert on relativity, the father of astrophysics and author of a succession of best-selling books on astronomy and the nature of the universe. At Cambridge, he was legendary for his sharp tongue, his pipe, his epic cycling expeditions and his habit of eating apples - core and all.

He lived with his mother and sister at the Cambridge Observatory and had no discernible private life.

Yet Eddington was heading for a fall. Having verified general relativity, he used that theory in a wrong-headed attempt to support his unswerving stance on the fate of the stars. In 1926, Eddington applied it to suggest that at the end of their lifespan certain stars might begin an eternal collapse, becoming infinitely tiny and infinitely dense. This would generate such an immense gravitational field that it would disappear into a deep well in space-time. Today, we call this a black hole. Eddington seemed to be way ahead of his time. But, in fact, he proposed it tongue-in-cheek, as an example of what unlikely scenarios might result if the theory was pushed to its logical conclusion. Four years later, a 19-year-old Indian prodigy, Subrahmanyan Chandrasekhar, came up with a mathematical proof for the proposal.

Eddington, the doyen of the astrophysical establishment and a supercilious old-school Englishman, refused to believe that the young colonial had anything to teach him. Instead of applauding Chandrasekhar, he dismissed as "absurd" the concept that something as huge as a star could disappear. At the time Eddington was engrossed in his life work - his "fundamental theory", which was an abstruse attempt to attain the Holy Grail of science, a theory that would encompass everything from atoms to stars. If Chandrasekhar's theory were true, it would destroy the basis of the professor's work. So Eddington brought the full weight of his prestige down on this challenge, using dubious arguments based on a questionable interpretation of general relativity in an attempt to undermine it. Most astrophysicists shared his view that the black-hole theory was implausible, though they looked askance at his arguments. Chandrasekhar failed to defeat Eddington in a series of debates and in the end he gave up studying the fate of stars. Ultimately, the feud seriously undermined Eddington's reputation. It stalled the quest to prove that black holes existed and was resolved only some four decades later, when Chandrasekhar revisited his great discovery.

Brilliant though he was, Eddington was seriously flawed as a human being.

Sadly, many of those who remember him tend to recall only this demeaning episode of his life. They forget Eddington's great moment on Principe, when, in May 1919, the stars spoke to him.

ÖйúAƬ

Arthur I. Miller is professor of history and philosophy of science at University College London and author of Empire of the Stars: Friendship, Obsession and Betrayal in the Quest for Black Holes , published by Little, Brown, ?17.99.