Isaac Newton Biography

World of Physics on Isaac Newton

Born in Woolsthorpe, Lincolnshire, England, Newton was a premature baby who was not expected to live. His father had died three months previous to the birth, and his mother remarried three years later, leaving Newton in the care of his grandparents.

Newton did not distinguish himself in school, and he was removed by his mother in the late 1650s to work on the family farm, but Newton proved a worse farmer than scholar. His uncle, however, encouraged the boy to go to Cambridge in 1660. Five years later Newton graduated, even though he had failed a scholarship exam in 1663 due to his lack of knowledge concerning geometry.

Newton returned to the farm shortly thereafter to escape the Bubonic plague, which at the time was decimating London. While at the farm in 1666, Newton saw an apple fall to the ground, and he began to ponder the force that was responsible for the action. While this story has often been considered to be the stuff of legends, Newton confirmed that it did indeed happen.

He first surmised that the apple fell because all matter attracts other matter. He then further theorized that the rate of the apple's fall was directly proportional to the attractive force which Earth exerted upon it. In addition, he suggested the inverse square law; force decreases according to the square of the distance from the center of Earth. Then he made a daring hypothesis, suggesting the force that pulled the apple was also responsible for keeping the moon in orbit around Earth.

When Newton made calculations of what the rate of fall for the moon should be, he came up short of what was actually observed and was quite disappointed. The problem was twofold; first, the radius of the Earth was not known with precision and the size Newton used was too small. Second, he was not absolutely certain he was correct in making his calculations based on the gravitational force at the center of Earth, as opposed to the surface. Because of these issues, he set aside his work on gravity for 15 years.

During this same time, Newton began to experiment with light, a book written by Robert Boyle having prompted his interest. Newton passed a beam of sunlight through a prism of glass and observed it was refracted into a spectrum. He passed the spectrum through a second prism, and the light was recombined into a white spot. For an unexplained reason, Newton did not notice any of the visible dark lines in the spectrum of the sun. It was not until over 150 years later that William Hyde Wollaston and Joseph Fraunhofer noticed the lines, and Gustav Kirchhoff realized they revealed the composition of heavenly bodies. Newton's experiments led him to conclude that light was comprised of a stream of particles that moved through an ether. Although this theory was later disproved, it was kept alive by Newton's influence for nearly a century.

In 1672 Newton was elected to the Royal Society where he reported on his experiments with light and its spectrum. While most members were impressed by his findings, physicist Robert Hooke, who had performed similar experiments and drawn different conclusions, dismissed Newton's findings as irrelevant. In response, Newton sent a scathing letter to Hooke, which was later published in the Royal Society's periodical. The feud between Hooke and Newton escalated, though the latter's increasing reputation in the British scientific community forced them to act cordially--at least in public. The two scientists' dislike for one another culminated in 1686 when Newton published his theory of universal gravitation. Hooke, who had outlined a similar theory in a letter seven years earlier, insisted that Newton had plagiarized his idea. In all fairness to Newton, it is possible he was unaware of Hooke's work, which was in any event fundamentally flawed. However, modern scientists now credit Hooke with the ideas that inspired Newton to develop his own, more accurate, theory of gravitation.

Newton became involved in yet another controversy, this time with the German mathematician Gottfried Leibniz. Both men had independently developed calculus, although each used different symbols and notations. Leibniz's notation, however, was considered superior and came to be preferred over that of Newton, causing a bitter controversy between the two. Their conflict quickly became a matter of national pride, and English scientists refused to accept Leibniz's version. Unfortunately this stubbornness kept them from significantly contributing to mathematics for nearly a century.

In the 1680s English astronomer Edmond Halley, a good friend of Newton, told him of Hooke's claim that he had discovered the laws concerning the motion of celestial objects. When Newton replied that he had made the calculations 15 years earlier but had lost interest, Halley convinced him to make the calculations again. With his friend's financial help, Newton published the results of his second effort in Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), which outlined the laws of gravity and motion. Though he now had calculus at his disposal, he apparently thought it more elegant to prove his deductions using only geometry.

In the Principia MathematicaPrincipia Mathematica, which appeared in 1687, Newton arranged Galileo's findings into three basic laws of motion: a body at rest remains at rest, and a body in motion remains in motion; force is equal to mass times acceleration; for every action, there is an equal and opposite reaction. These three laws allowed Newton to calculate the gravitational force between Earth and the moon. He asserted these laws acted upon any two objects in the universe, establishing the law of universal gravitation, and proceeded to estimate, quite accurately, the masses of Jupiter and Saturn. The Principia Mathematica not only explained Johannes Kepler's laws of planetary motion, it elegantly showed how celestial bodies and earthly objects followed a single law; the unity of heaven and Earth were at last grasped by reason.

The book was written in only 18 months and apparently exerted an enormous strain on Newton. Coupled with the continual controversy surrounding him, Newton suffered a nervous breakdown in 1692. Although he recovered, he was never the same. He went on to write another book, Opticks, which covered his work on light; however, he waited until after Hooke's death before printing it in 1704. In 1705 Queen Anne knighted him.

Newton died on March 20, 1727, at the age of 84, and his vast influence upon science continued, later rivaled only by that of Charles Darwin and Albert Einstein. In a letter written to Hooke, Newton stated, "if I have seen further than other men, it is because I stood on the shoulders of giants."