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add more on his physics
Newton never married, but he brought his niece to London as his hostess and lived in upper class style.
Newton never married, but he brought his niece to London as his hostess and lived in upper class style.
==annus mirabilis==
The year 1666 is known as Newton's ''annus mirabilis'' (miraculous year--more precisely the two years 1665-1666), about twenty-four years of age. He latter recalled, "For in those days I was in the prime of my age for invention & minded Mathematicks & Philosophy more than at any time since." (By "philosophy" he meant physics.)
===Calculus===
Critical to his work on calculus was discovering the binomial theorem which expresses areas under curves as infinite series; when the curve is expressed as algebraic formula, he had invented integration. He followed that with a method for differentiation, and came upon the fundamental theorem of the calculus, that of the inverse relation of differentiation and integration. Having invented the calculus, he put aside mathematics for two years and turned to physics.
Although Newton had communicated his discoveries in the calculus privately, he did not publish anything formal about it until finally, in 1704, he published ''Opticks''. In the meantime the German mathematician [[Gottfried Wilhelm Leibniz]] had developed his own very similar version of the calculus. Although he acknowledged that Newton was earlier, a nasty priority conflict broke out in the 1710s. Newton and his (mainly English) followers accused Leibniz of plagiarism, and the Germans retaliated in kind. The modern view is that both mathematicians discovered the calculus independently. The symbolism in modern use comes from Leibnitz and 18th century French mathematicians.
===Optics===
While waiting out the plague he began to investigate the nature of light. White light, according to the prevailing theories, was homogeneous. His first experiments with a prism provided the true explanation of color. Passing a beam of sunlight through a prism, he observed that the beam spread out into a colored band of light (spectrum). While others had undoubtedly performed similar experiments, it was Newton who showed that the differences in color were caused by differing degrees of refrangibility. A ray of violet light, for example, when passed through a refracting medium, was refracted through a greater angle than a ray of red light. His conclusions, checked by ingenious experiments, were that sunlight was a combination of all the colors and that the colors themselves were monochromatic (his term was "homogeneal"), and separated merely because they were of differing refrangibility.
[[Image:Opticks.jpg|thumb|left|280px]]
== Gravity ==
== Gravity ==
Newton developed the [[Theory of Universal Gravitation]], more commonly known as gravity, when, according to legend, a falling apple struck him on the head. He realized that the same force that pulled the apple to the ground could be what keeps [[Jupiter]]'s moons in orbit. His theory stated that all matter is attracted to matter by a force, whose strength increases proportionally to the mass of the objects involved, and inversely proportional to the squared distance between them. Newton's theory is based on action-at-a-distance which has always been opposed by some scientists, and now most physicists endorse the very different [[theory of relativity]]. Both theories predict identical results at small scales, similar results at the scale of the [[solar system]] and very different results at [[Cosmology|cosmological]] scales beyond the [[solar system]].
Newton developed the [[Theory of Universal Gravitation]], more commonly known as gravity, when, according to legend, a falling apple struck him on the head. He realized that the same force that pulled the apple to the ground could be what keeps [[Jupiter]]'s moons in orbit. His theory stated that all matter is attracted to matter by a force, whose strength increases proportionally to the mass of the objects involved, and inversely proportional to the squared distance between them. Newton's theory is based on action-at-a-distance which has always been opposed by some scientists, and now most physicists endorse the very different [[theory of relativity]]. Both theories predict identical results at small scales, similar results at the scale of the [[solar system]] and very different results at [[Cosmology|cosmological]] scales beyond the [[solar system]].
Newton had already made great progress in his devising "method of fluxions" (the infinitesimal calculus). During the plague years he recorded his first thoughts on gravitation, inspired by watching an apple fall. It fell straight down--why was that? He was trying at that time to determine what type of force could hold the moon in its path. The fall of the apple led him to think that it might be the same gravitational force, suitably diminished by distance, that had acted on the apple. Thereby he discovered the law of [[gravitation]] (attraction is proportional with [[inverse-square law|inverse distance squared]]). He verified his conjecture approximately by a numerical calculation. He did not, at the time, pursue the matter, because the problem of calculating the combined attraction of the whole earth on a small body near its surface was obviously one of great difficulty.<ref> The problem was enormously simplified when he later used his calculus to prove that, for purposes of gravity, a uniform sphere of any size can be considered as a single mass located at one point, the center.</ref>
Newton struggled with how to conceptualize gravity. He had early rejected Descartes's vortex account of the cause of the motion of the planets. Descartes had argued that forces were transmitted through contact and that this required that matter be continuous and that hence there could be no vacuums. As early as 1665 Newton attempted to find a physical explanation of the cause of gravity but never found a suitable answer. As Newton said later in his ''Principia,'' "I have not as yet been able to deduce from phenomena the reason for these properties of gravity, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy". Thus Newton offers no explanation of gravity but shows through his mathematics that it "acts" in accordance to the mathematical laws he offers us in the ''Principia''. This was a difficult approach for his contemporaries to accept. [[Robert Hooke]], in particular, saw experimentation as the heart of science and disapproved of Newton's focus on theory and mathematics.
==Three laws==
see [[Classical mechanics]]
Later in life, as a holder of the Cambridge [[Lucasian chair]] of mathematics, Newton worked out his initial ideas into a set of mechanical laws, with his second and most important law: Force is mass times acceleration (<math>\scriptstyle F = m a~</math>). Newton was the first to understand the concept of [[inertial force]]s, notably the [[centrifugal force]], although [[Christian Huyghens]] was close to understanding this effect. In 1684 Newton proved that [[Kepler's laws]] follow from his own second law in conjunction with his gravitational law. This proof completed the astronomical revolution initiated by [[Copernicus]].
==Principia Mathematica==
Newton avoided publishing his results, preferring to communicate them to close colleagues. It took [[Edmond Halley]] great efforts to convince Newton to write his opus magnum ''Philosophiae Naturalis Principia Mathematica'' ("Mathematical Principles of Natural Philosophy" written in Latin, it was called the ''Principia'') that appeared in 1687. A second expanded edition appeared in 1713. It was a work on [[Classical mechanics|mechanics]] that used Newton's new principle of universal gravitation to explain falling bodies on the earth and the motions of planets and comets in the heavens. The first part covers dynamics and includes Newton’s three famous laws of motion. The second part concerns fluid motion; the third part deals with "the system of the world" ("De mundi systemate"), that is, the unification of terrestrial and celestial mechanics under the principle of gravitation and the explanation of Kepler’s laws of planetary motion. the material was very advanced and difficult, especially since the underlying calculus was deliberately hidden from view. Scientists across Europe immediately recognized its importance and tried to read it.
==Newtonianism==
Feingold (2004) explains the rapid dissemination of Newton's science came first via the members of the Royal Society, both British and Continental. The scientists, mathematicians, and philosophers of Germany, Holland, France, and Italy read the editions of the ''Principia'' and the ''Opticks'' and taught the ideas to their students. Newton's work was widely accepted, except in Italy, where the Catholic Church, having silenced Galileo, tried as well to suppress Newton's ideas. Despite the importance of Descartes to the French, Newton carried the day in France. [[Voltaire]] in particular made Newton the great hero of the modern world of ideas. Voltaire's ''Elemens de la philosophie de Neuton,'' (1737), was a success that rendered Newton intelligible and his work accessible, to the nonspecialists and amateurs who flourished in the [[Enlightenment]]. In Germany [[Leibniz]] praised Newton's ''Principia'', but was uncomfortable with Newton's position regarding gravity. It was philosophically untenable to merely dismiss the problem of its cause. French scientists, especially [[Pierre Simon Laplace]] (1749-1827) developed and systemized Newton's ideas into modern [[Classical mechanics]] in the late 18th century.<ref>Roger Hahn, ''Pierre Simon Laplace, 1749-1827: A Determined Scientist.'' (2005). 310 pp. </ref>
Newton's science dominated science and educated thought throughout the 18th century, being seen as the highest achievement of pure reason and classical culture.<ref>Feingold, ''The Newtonian Moment'' (2004); Larry Stewart, ''The Rise of Public Science: Rhetoric, Technology, and Natural Philosophy in Newtonian Britain, 1660-1750.'' (1992)</ref> In the 19th century, however, Romantic scientists went in entirely new directions, exploring non-Newtonian topics in electricity, magnetism and thermodynamics, and in mathematics turning to topics unrelated to calculus, like group theory. The leading German Romantic, [[Wolfgang von Goethe]], even tried to challenge Newton's optics.
== Religious Beliefs ==
== Religious Beliefs ==