Few men have ever been catapulted to global superstardom with such suddenness as Albert Einstein. One moment, he was a professor in Berlin, known among his peers but pursuing ideas about the nature of gravity that were understood by only a handful; the next, he was the most famous scientist in the world, perhaps the most famous man in the world.

For this, he owed the discipleship of Arthur Eddington, the first and most loyal supporter of his General Theory of Relativity. The paradox is that before Einstein’s overnight introduction to fame in 1919, the two men had never met and were in many respects polar opposites: Einstein was a non-believer, a bohemian with an eye for the ladies; Eddington was a straitlaced Quaker who lived with his sister and constantly struggled to square science and God. One was a dreamer of genius; the other an experimentalist devoted to careful measurement and empirical truth.

Physics commonly advances through the union of these two castes of mind, often embodied in different people. But seldom has it done so when the two bodies are divided by a world war that made communication almost impossible. Not only was Einstein German, but he was proposing a theory that would dethrone Isaac Newton from his position as the master of the universe: two reasons for British scientists to decry him.

Einstein and Eddington, starring David Tennant as Eddington and Andy Serkis as Einstein, narrows the gap between the two men by showing that neither could swallow the patriotism of the warmongering blimps who surrounded them in Cambridge and Berlin. Einstein is horrified by stumbling across a demonstration in which poison gas is tested on pigeons. Eddington, a conscientious objector, is spat upon by a mob when he protects German shopkeepers from harm at the height of anti-German sentiment. Did this actually happen in Cambridge? Maybe.

For connoisseurs of documentary-dramas, Einstein and Eddington offers some delicious treats. A stranger approaches Einstein in Zurich in 1909, offering him a prestigious chair in Berlin. “Max!” exclaims Einstein, “Max Planck!” So that’s who he is. Thanks for telling us, Albert. When Einstein duly arrives in Berlin, Planck introduces him to another scientist with the words: “Fritz Haber you know, of course?” The answer is clearly not going to be “No, as a matter of fact I’ve never heard of him.” Haber then discloses that he is working on what we now know as the Haber Process for capturing atmospheric nitrogen. Handy for making explosives, Einstein responds. Nudge nudge, wink wink, say no more. But in the absence of a narrator, clunking dialogue is occasionally unavoidable.

A more serious objection might be to ask whether Einstein really was so unknown within science before Eddington came to his rescue. In 1905 he had written three papers of such originality and merit – one of them outlining the Special Theory of Relativity – that some perceptive scientists already realised his brilliance. Why else would Planck have sought him out, a German who had left Germany and taken Swiss nationality, and insisted he come back to Berlin?

At the heart of Einstein’s genius is gravity. His 1916 paper outlining his General Theory of Relativity – the name is a little confusing, but it’s about gravity – had been smuggled to Eddington at the height of the First World War. The drama makes Planck the reluctant go-between, though history has generally identified Willem de Sitter. Newton had identified that the same force was responsible for the movement of the planets and for apples falling from trees, but had left its nature undefined. His theory worked like a dream, and is still good enough for 99.9 per cent of human activity. But Eddington was nagged by the odd 0.1 per cent where it went wrong. Why couldn’t Newton’s Laws of Motion explain the orbit of Mercury with perfect accuracy? And how did the force of gravity act through interstellar space, with no intervening matter to propagate it?

Einstein responded to these challenges by ripping up the rulebook. Time became a variable, as did mass. Time and space were combined into spacetime, the warp and woof of the universe, whose shape was distorted by nearby masses such as planets so as to change the course of an object careering by. A marvellous moment in Einstein and Eddington comes when Eddington clears the dinner table, to the dismay of his long-suffering sister, and uses the tablecloth, a bread roll and an apple to demonstrate the principle. This is so beautifully done I raised a silent cheer.

Eventually, as students of astronomy already know, Eddington travelled to Principe in West Africa in 1919 to watch an eclipse of the Sun. If Einstein was right, the mass of the Sun would bend rays of light passing close to it. While the Sun was eclipsed, it should be possible to observe the light from stars in the same area of the heavens, which would normally be too faint to see. A photograph taken of these stars could then be compared with the same group taken when their light was not passing close to the Sun. If the position of the stars shifted between the two plates, Einstein was right: if not, Newton still ruled supreme.

This wonderful experiment ranks with the greatest ever undertaken. In fact, its results were not quite as clear-cut as Einstein and Eddington pretends, but we’ll let that pass. The conclusion drawn in London, at a meeting at the Royal Society, was that Eddington’s plates did prove Einstein right, and time has proved this conclusion justified.

Einstein, by then worn-out and ill, awakes to find the world on his doorstep. In a moment, everything has changed. Newtonian certainties have been replaced by a much more demanding theory that probes more deeply into nature and finds truth by turning common sense on its head. A century later, the General Theory of Relativity is still as avant garde as it was in 1919; still, for most people, a puzzle too far. What a man. And what a disciple.

General relativity: a guide

Newton showed that masses attract one another, but did not explain why. Einstein’s General Theory of Relativity argues that the attraction occurs because objects distort space, causing it to curve. Other objects are drawn inwards by this curvature, like a golf ball spiralling towards a pot-bunker.

His Special Theory, in 1905, had already suggested time was not invariant, but depended upon the speed of the observer relative to the clock – hence Relativity. The General Theory proposed that gravity, as well as motion, could affect both time and space.

General Relativity predicts the bending of starlight by gravity, the existence of black holes, and is the basis of the Big Bang theory of the origins of the Universe. However, E = mc2, the equation showing that mass and energy are equivalent, arises from the 1905 Special Theory.

— Einstein and Eddington, tonight, BBC Two, 9.10pm

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