Dairy

STS 112 Newton

David Mercer 2013

Portrait of Sir Isaac Newton

Newton (1642-1727)

• Newton’s work in many texts interpreted as the triumph/ pinnacle of the Scientific Revolution

• Most importantly his work the ‘Principia’

short for ‘Philosophiae Naturalis Principia Mathematica’ (The Mathematical Principles of Natural Philosophy) published in 1687 often taken as the single most important book published in the history of scientific thought.

Newton’s contributions • Contributed to theories of optics, helped develop various forms of calculus, helped

develop new ways of doing experiments • Provided a coherent set of mathematical explanations to synthesise the work of

Galileo and Kepler and others • Solved most of outstanding problems of physics of the time, unifying celestial and

terrestrial physics this included a decisive solution to the problems of planetary motion. • Famous in his own time. • Newtons variation on the mechanical philosophy ( with its Neo-Platonist throwbacks,

of action at a distance, immaterial forces etc) influenced new theories of electricity, early chemistry and other ‘emerging’ sciences of 18th Century

• Many of the generation of scholars that followed Newton suggested that his contributions to Natural Philosophy could be applied to understanding all phenomena including society (even if they didn’t really understand the maths)

• This image of the power of Newton’s methods would be an influence on the so called Enlightenment Philosophers who became important in the generation after Newton’s death.

Universal Gravitation

• At the centre of many of these contributions was Newton’s theory of universal gravitation and 3 laws of motion.

Universal Gravitation • Imagine a simple universe, in an infinite empty space there are 2

mathematical points that have mass. The masses will attract each other with equal and opposite forces, this force can be measured by multiplying the masses of the two bodies together and then dividing the result by the square of the distance between the two bodies.

• This force does not need to be explained by atoms or corpuscles or some kind of mechanism it is an intrinsic quality of matter that has been there since the matter came into existence.

• Matter exerts an attraction instantaneously and at a distance.

3 Laws of Motion

• 1. Law of inertia: a body in motion in straight line at a constant speed will remain in that motion, in that line at a constant speed unless acted on by an outside force.

• 2. Force equals mass, times acceleration , ie: if you apply force to a body it accelerates.

• 3. Every action corresponds with an equal and opposite reaction.

(see J.Schuster, The Scientific Revolution chapter 21)

Universal Gravitation and 3 Laws: using approximations and mathematical calculation explain:

• Kepler’s laws of planetary motion, earth and other planets orbits

can be explained largely in terms of their gravitational attraction to the Sun. We can even speculate on the earth’s mass.

• Galileo’s terrestrial law of free falling objects accelerating at a mathematically describable rate.

• Problems like the tides can be addressed by thinking in terms of the gravitational attraction between the earth, moon and sun.

• Problems of the earth’s very slow (1 x every 25,000 year wobble on its axis) precession of the equinoxes. The Earth was like a spinning top slowly falling over.

• Why the earth is a little fatter at the equators than the poles ( actually a prediction ) was confirmed.

Example: these ideas applied to Planetary Motion

• Planetary motion is a mixture of inertial straight line motion and centripetal force or attraction to the centre.

• Imagine a ball tied to string with if its straight line inertial motion is balanced by it being drawn back by the string (gravity) the observed effect is a rotational motion

• Newton asked readers to imagine a cannon ball being shot off a tall mountain if it had enough straight line motion imparted on it to compensate for its attraction back to earth it would become a satellite orbiting the earth. Newton suggested we could think of the motion of the moon in similar terms.

Apples

• As an older man Newton recounted the story that some of these ideas came to him in his youth when he was hit on the head by an apple and reasoned that the same force that drove the apple towards the earth must also be the same force that drove the moon to in a sense fall towards the earth.

• Unlikely as a youth, even as a genius, he had actually got the maths and theory worked out for universal gravitation and his 3 Laws.

• A feature of Newton’s academic life was to take significant periods of time out from doing ‘physics’ and astronomy to do alchemy numerology, theology and other intellectual pursuits and withdraw from social interactions

• Most historians argue that the actual detailed formulations of Newton’s ideas occurred much later released in dribs and drabs and finally in the Principia partially in response to Newton disdain for and rivalry with another Natural Philosopher Robert Hooke.

• Hooke had been exploring and publicising some similar ideas to Newton but didn’t have the same level of mathematical skill or theoretical imagination

Newton in Context

• Universal gravitation was in its own time and even today a rather strange and challenging concept

• We need to remember mechanical philosophy is taking over and popular figures such as Descartes are arguing very strongly for causes and effects to be able to explained in terms of (atoms)corpuscles.

• Many mechanists preferred to explain planetary motion in terms of the interactions of swirling vortices of matter

• They expressly opposed theories like universal gravitation which relied on ‘action at distance’ and was an intrinsic quality of matter. They thought much of Newton’s work was a throw back to Magic and Neo- Platonism (just Kepler mark 2!)

• What actually was universal gravitation was it just an occult magical

quality?

Newton’s Post Mechanical Philosophy

• Newton sometimes like a mechanical philosopher ie: famous experiments with light exposing light made up of many colours challenged the idea of light as a pure divine force… but….

• At the same time in a rather Kepleresque fashion suggested things like light, magnetism, gravity, chemical force, behaved according to beautiful harmonious mathematical principles, were immaterial causal agents and were created by God as things operating at a superior level to Corpuscles.

Explanations for Newton arriving at his Post Mechanical Philosophy of Nature

• Newton sufficiently unusual and famous has inspired a variety of interpretations

• Psycho-History ! Historian Frank Manual ‘Portait of Isaac Newton’ Psychoanalysis of Newton. His biographical details important.

• Newton born on Christmas day 1642( same year as Galileo’s death) Newton’s father died a number of months before he was born. Mother remarried when he was three years of age and left him to brought up by his maternal grandmother has little contact with his mother. His mother was there but ‘acted at a distance’

• In later life never married spent periods as a recluse possibility he never had sexual relations very few proper friendships.

Psycho- Newton ?

• Newton believed it was significant he had been born on Christmas Day , he considered he was superior to his colleagues even gifted with divine insight. Never knowing his father but being a gifted son of God.

• Despite being immensely respected by them academically Newton was brutal and dismissive of his peers

• Newton himself was powerful but considered himself to be acting at a distance from his peers.

More substantial context

• First generation of scholars growing up academically where Copernicanism and different versions of mechanical philosophy were widely accepted. There were therefore opportunities to reflect on possible strengths/ weaknesses in mechanical philosophy without having to provide continuous reference back to Aristotelian concepts.

• The emergence in the 1650’s -1660’s of new (non-Aristotelian ) formal academic institutions such as the Royal Society (influenced by Bacon’s rhetoric of developing new knowledge for human betterment ) where learned gentleman could critique, promote, debate and develop their new experimental, mechanical influenced versions of natural philosophy.

Cambridge Neo-Platonism

• Whilst studying at Cambridge University Newton came under some of the influence Cudworth and Moore who held Neo- Platonist views and were critics of various aspects of Mechanical Philosophy

• Uncomfortable with Descartes strict dualism between Humans and other forms of life for example.

Religious conflicts

• Still period of intense religious and political debate eg: Newton working in decades after 20 years of civil war and political/religious turmoil, eg Cromwell and the ultimate restoration of the Stuart Monarchy in England.

• Newton himself held unusual religious viewpoints • He was pre-occupied with the religious significance of the

mechanical philosophy

• Whilst in many places Newton said that he hoped mechanistic principles could ultimately explain all of nature… in others he suggested that mere mechanical causes were inadequate to understand the beauty of the universe which indicated the existence of God.

The need for an Intelligent and Powerful Being

• “ This most beautiful system of sun, planets and comets could only proceed from the counsel and dominion of an intelligent and powerful Being”

Newton in Preface to the Principia, quoted in Kearney ‘Science and Change 1500-1700’ p188 Things like the actual distribution of the stars ie: they’d been placed

far enough from each other so gravity wouldn’t make them collapse into each other, and the distribution of the planets in the solar system, including things like the earth having just the right distance from the sun to allow us to live comfortably, and the continuous operation of gravity as an immaterial force all suggested an

intelligent designer constantly present in the universe.

Also Neo-Platonic musings

• In other drafts of the Principia Newton sounds distinctly Kepler like in suggesting that universal gravitation and his laws build on Pythagorean traditions of revealing divine mathematical harmonies:

“ To some such laws the ancient philosophers seem to have alluded when they called God Harmony and signified his actuating power harmonically by the God Pan’s playing upon a Pipe and attributing musick to the spheres, made the distances and the motions of the heavenly bodies to be harmonical and represented the Planets by the seven strings of Apollo’s Harp.”

Newton quoted in Kearney Science and Change 1500-1700, p191.

Technical Limits on Mechanical Philosophy

• Certain Phenomena such as light seemed to not quite follow mechanical philosophy as put forward by Descartes.

• Newton observed that light bouncing off a mirror obeys mathematical / geometric laws eg the angle of incidence equals the angle of reflection for example.

• Newton suggests that if we assume that light and the mirror were made up from corpuscles light should in fact be scattered

• Newtons answer was that the light particles don’t actually hit the mirror but must give off a short-range repulsive force acting at a distance which creates a thin ‘force field’ which allows the light particles to be repelled as a coherent beam from the imperfect surface of the mirror .

Overview

• Newton adopts many of the attitudes of the mechanical philosophy eg: he talks in terms of corpuscles, he is a Copernican, he believes the universe can largely be explained by mechanical and mathematical principles, he is interested in doing experiments and further developing experimental methods, he is interested in unpacking nature, believes in the value of natural philosophy to better the world. But….

• He talks in terms of the need for God as not only the creator of the universe but working in the universe through immaterial forces such as gravity

• Gravity doesn’t need a mechanical explanation it is one of a small number of important immaterial forces which need to be added to the Mechanistic world picture

• In some of his work he talks in mystical Neo-platonic terms reminiscent of Kepler including that he is divinely inspired.

• Spends considerable periods of life engaging in Alchemy, Numerology and Theological speculation.