Mythconception: Newton's Apple

09 May 2017

APPLE-TREE

A red apple in a tree

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Each week, The Naked Scientists get to the bottom of some suspicious science. Kat Arney has been getting her teeth into a fruity legend with this mythconception...

Kat - The history of science is peppered with fascinating and funny anecdotes explaining how great minds hit upon their brightest ideas. One of them is the image of Sir Isaac Newton sitting quietly under an apple tree, only to be bonked on the head by a falling fruit and inspired to come up with the theory of gravity. It’s a wonderful and well-loved image that tells a simple story, but sadly it’s simply not true.

The legend starts in the late 1660s, when Newton had been sent back to his childhood home at Woolsthorpe Manor near Grantham in Lincolnshire due to an outbreak of bubonic plague at Cambridge University where he was studying.

According to William Stukeley, who wrote a biography of Newton in 1752, Newton himself recounted that “After dinner, the weather being warm, we went into the garden, & drank tea under the shade of some apple trees… he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind…. occasion’d by the fall of an apple, as he sat in a contemplative mood.

“'Why should that apple always descend perpendicularly to the ground,' thought he to himself. 'Why should it not go sideways, or upwards? But constantly to the earth's centre? Assuredly, the reason is, that the earth draws it. There must be a drawing power in nature.'"

Nice as it is, something doesn’t quite add up here. Newton only told Stukeley the story in 1726, a year before his death in 1727 and a full 60 years after the alleged ‘apple incident’. The French writer Voltaire also mentioned the story in an essay penned in 1727, saying "Sir Isaac Newton walking in his gardens, had the first thought of his system of gravitation, upon seeing an apple falling from a tree."

It seems strange that Newton wouldn’t have mentioned such a key moment sooner - although maybe he was embarrassed about something so humble leading to such a great idea. As a clincher, Newton’s own notes show that he was grappling with ideas about gravity before he went back to Woolsthorpe.

Like all good legends, the story of Newton’s apple tree probably has a root in the truth - watching the apples falling from the trees might have helped to focus his mind on the nature of gravity and shape his theory, we can certainly say that it probably wasn’t an instant inspiration - and definitely not a bonk on the head.

But even if it’s a bit of scientific fabrication, the story of Newton’s Apple is still a great piece of scientific communication - it’s certainly a handy and easily-understandable example of gravity that most people would have witnessed, which doubtless Newton used when explaining his theory.

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