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Today’s research into fusion energy owes a huge debt of gratitude to Arthur Eddington – the English astronomer, physicist and mathematician.

For it was 100 years ago this August that Eddington delivered his momentous lecture about fusion and the Sun at the 1920 annual meeting of the British Association for the Advancement of Science in Cardiff.

Arthur Eddiington

Arthur Eddington – photo credit: George Grantham Bain Collection, Library of Congress Prints and Photographs Division Washington, D.C. / Public domain

Basing his conclusions on the then-recent formulation (and now world-famous equation) of E=mc2 by Albert Einstein, Eddington explained how the stars drew their endless energy from the fusion of hydrogen into helium.

It was ground-breaking as previously the answer to what made the sun endlessly shine was a matter of conjecture. From the Ancient Greeks – who believed the Sun was a flaming ball of metal – to 19th century scientists, who thought gravitational contraction was the explanation, the truth eluded everyone until Eddington stood up to deliver his lecture in Cardiff.

During the lecture Eddington declared: “A star is drawing on some vast reservoir of energy by means unknown to us. This reservoir can scarcely be other than the subatomic energy which, it is known exists abundantly in all matter; we sometimes dream that man will one day learn how to release it and use it for his service. The store is well nigh inexhaustible, if only it could be tapped.”

Bringing the Sun to Earth as an energy source has turned out to be one of the most difficult quests in science, but as researchers around the world vie to build fusion reactors to power the planet, Eddington’s dream finally looks like it could become a reality. Find out more about Eddington’s discovery and the story of fusion research in our video to mark the 100th anniversary of his famous lecture.


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