an apple falls from isaac newton's tree -- 3/6/17

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Today's selection -- from 1666: Plague, War and Hellfire by Rebecca Rideal. In 1666, a bubonic plague had forced University of Cambridge to close its doors and send all of its students back to their homes. One especially precocious 23-year-old student used this free time to redouble his studies, which included the world-changing reflections he made one afternoon while resting under an apple tree:

"[On a farmstead known as Woolsthorpe Manor], during the spring [English] trees [known as the Flower of Kent] would be covered in flushed pink-white blossom and by late summer and early autumn their branches would be heavy with large sweet apples, used for cooking. The farmstead ... was about a mile to the west of the Great North Road and located in an area of agricultural richness. Up until 1642, the limestone building and working fields had been owned by a prosperous yeoman farmer who had died just two months before the birth of his only child. This child was now a twenty-three-year-old man named Isaac Newton and, on a hazy autumn day in 1666, he sat beneath one of the apple trees in, as he later described, 'a contem­plative mood'.

"For all its rural beauty, Woolsthorpe was not where Newton wanted to be. He had in fact attempted to return to his university studies earlier that year, but the plague in Cambridge had proved to be far too virulent. Instead, he had new shelves constructed at his family home to accommodate the books he had brought back from Cambridge, and made frequent trips to the library at the nearby parsonage in Boothby Pagnell. Newton might have been in exile, but he did not spend his time idly. Filling the pages of his notebooks with the results of experiments and observations, his time at Woolsthorpe resulted in some of the most significant scientific and mathematical discoveries of the entire century. As he later reflected, 'in those days I was in the prime of my age for invention'.

"Despite having no formal training in mathematics, Newton had created the first thorough work on calculus and geometry, by form­ing equations to measure integration (areas bound to curves) and differentiation (tangents to curves); a genre of mathematics that he referred to as 'the calculus of fluxions'. He had also experimented with optics, using a triangular glass prism to unravel 'the celebrated Phaenomena of colours'. Darkening his chamber except for a thin slice of light through his window, Newton placed the glass prism at the light's entrance so 'that it might be thereby refracted to the opposite wall'. In doing so, he discovered that white light consisted of integral composite colours, which revealed themselves when split. This discovery ran contrary to Robert Hooke's musings in his book Micrographia, which suggested that the colours were a result of, rather than revealed by, the prism. Individually, these were signifi­cant advances. Combined, they represented a remarkable achieve­ment. Grouped with his final discovery of 1666, they marked Newton out as a scientific great.

"Whatever he was contemplating as he sat under the apple tree on this autumnal day was brought to a sudden halt when, above him, a stem holding one of the plump apples strained and snapped. The speckled red fruit thumped to the ground and, in a flash, Newton had a groundbreaking epiphany. It became clear to him that the fruit had been drawn to the ground because gravitation worked to pull things together and hold everything onto the Earth, and that its gravitation must extend beyond the sky, into space, and to the moon itself. Following where Galileo and Kepler had led, and Einstein would later follow, in 1666, Newton had started:

'... to think of gravity extending to the orb of the Moon ... and deduced that the forces which keep the Planets in their Orbs must be reciprocally as the squares of their distances from the centres about which they revolve ...'

"At least, that is how the incident was told to, and recorded by, at least four different people during the course of Newton's long and illustrious life. With its echoes of the tree of knowledge in the Garden of Eden, the strong image of a maverick genius unrav­elling the mysteries of the universe in isolation from wider soci­ety is difficult to shake. While there is no reason to doubt that Newton had something of an epiphany in his garden that year, his initial leap of understanding was followed by painstaking work to develop the mathematical equations and models that got to the crux of his understanding of gravitation. In fact, Newton's contribution was significant not for its eureka moment (others, including Robert Hooke, had made and would continue to make passing theories about the pull of objects and gravity), but for the fact that it moved away from, as the French scientist Alexis Clairaut wrote in 1727, 'a truth that is glimpsed' to 'a truth that is demonstrated'. Through the scrupulous use of calculus, Newton would demonstrate in his seminal text Philosophae Naturalis Principia Mathematica (1687) that gravitation and the movement of objects was demonstrable by mathematical connections."