Jennifer Bishop November 6, 2007 ILS Homework Notes: Newtonianism Course Reader: Pgs. 221-226 (Newton’s The System of the World) “The System of the World” was Newton’s first attempt to write about centripetal forces at work in the natural world Introduction to the book Newton says he will address mathematical principles, not philosophical principles Originally composed the third book in the “popular method” Decided to make his book into mathematical proofs He wants his books to be read only by those who have first mastered the material in the preceding books, so they aren’t so judgmental From “The System of the World” All the ancients agreed that the motions of the celestial bodies took place in a space free of resistance (solid orbits) Comets can’t be explained by solid orbits- can only be viewed once every revolution This led Newton to question what forces were at stake The Principle of circular motion in free spaces Motion must come from the action of some force This force is called centripetal force- a force directed towards some center The Action of Centripetal Forces Newton explains that when a stone is projected, it is made to curve The greater the velocity when it is projected, the farther it goes before falling Newton thought that a moving body tends to move in a straight line unless something forces it to move otherwise All celestial bodies are influenced by the same centripetal force “moon test”- the moon’s curved motion around the earth follows the same motion pattern as an apple at the surface of the earth Newtonian gravity- a universal attractive force that affects the motion of all material bodies, whether terrestrial or celestial From “Opticks”- Query 31 The variety of motion in the world is always decreasing There is little motion in the world besides motion that are the result of a will God set the motions in order If this is true, we shouldn’t seek any other origin of the world If this is true, we shouldn’t pretend the universe grew out of chaos “blind fate” could never make the planets move the same way in concentric orbs- God must be the reason D: Pgs. 149-167 (Cartesians and Newtonians) Cartesian Natural Philosophy in France Christian Huygens One of the leading figures of the Royal Academy of Sciences in Paris Cared about what both mathematical and mechanistic approaches could be used for, AND what practical results they yielded Thought gravity resulted from the “steady, uniform acceleration of a falling body” Wrote On the Motion of Colliding Bodies (on collisions) Wrote On Centrifugal Force (analyzed outward-motion tendencies of bodies) His writings were mostly hypothetical Sought explanations that were “intelligible”, or that made perfect sense Only size, shape, and motion are considered when discussing gravity Huygens saw what he was doing as a continuation of Descartes’ Cartesiansim BUT Huygens disregarded key points of Descartes’ Cartesianism Huygens took Descartes’ metaphysical arguments regarding the nature of matter to describe only the limits of the human mind He said human beings couldn’t understand explanations in terms other than the behavior of matter in motion there could be truer explanations of phenomena that won’t serve humans as explanations because we can’t make sense of them treated light as a form of motion justifies the use of nothing but mechanical motions interpreted light as longitudinal waves the speed of the waves and the way in which they combine are most important Huygens treated parts of phenomena individually, not as a whole Jacques Rohault Promoted the ideas of Descartes with mathematical and experimental demonstrations of phenomena Wrote Treatise of Physics Both reason and experience are important in creating knowledge about nature Mocked the obscurity of Aristotelian philosophy Didn’t like the separation of math and philosophy Includes constituents of physics, cosmography, earth, and the human body Rohault wanted to provide plausible explanations of phenomena The Salons of Paris Upper-class retreats for intellectuals Presided over by women Both women and men participated in their activities Elite “open houses” each week took place at a gentleman’s house, presided over by his wife; prestigious figures always present Salons allowed women to discourse with men about otherwise-restricted matters Women weren’t allowed university education Women took Descartes’ position: “the mind is distinct from the body” there is no difference between the female and male mind the mind has no sex Newtonian Alternatives Gottfried Wilhelm Leibniz Proposed a “pre-established harmony” between mind and body God arranged the world so that whatever the mind experiences is matched by the physical/material world Isaac Newton His “wonderful year”- invented calculus, published his work on lights and colors, began his work on gravitation Wanted to know what the centrifugal force at the earth’s surface would be Convinced by Edmund Halley to publish his Mathematical Principles of Natural Philosophy Huygen’s results on centrifugal force played a key role in this work Newton wrote in geometrical form Never identified the source of gravity by doing this, Newton avoided the issue of whether gravity is an attractive or repulsive force BUT, Newton treated gravity as an attraction towards earth Newton attributed the idea of force to GOD God makes bodies move according to gravitational laws There is no intermediate physical cause, only GOD God necessarily exists….he is always and everywhere Force is the cause of “nothing else than the Wisdon and Skill of a powerful ever-living agent” (Newton) Newton was supported by the Boyle Lectureship People in this society made use of Newton’s views on nature and on God’s relationship to it Nearly all the lectures were published in book form Newtonianism Newton became President of the Royal Society, and ruled the Society until his death People in the society supported Newton’s work because most owed their positions to him Personal patronage within the Royal Society bred loyalty Other philosophers had problems with Newton’s book They thought he hadn’t really presented a work of natural philosophy He had presented a mathematical description “dressed up” as natural philosophy There was no physical explanation of gravity The Leibniz-Newton debate Both men debated about gravity through a published correspondence between Leibniz and Newton’s surrogate, Samuel Clarke Leibniz had a problem with Newton’s view of God as an “imperfect clockmaker” the perfection of the solar system is compromised by mutual gravitational attraction between planets Newton liked this imperfection God’s intervention is needed once in a while, God fixes the system before it gets out of control this shows that he really exists Jennifer Bishop November 6, 2007 ILS Lecture Notes: Newtonianism Newton is seen as a “hero” now, but at his time, he wasn’t recognized Why was he received in this way? Social context Philosophical context (mechanical philosophy) Theological context (the role of God in Newton’s cosmos) Newton and the Color Controversy Isaac Newton (1642-1727) “A New Theory about Light and Colors” (1672) Student at Cambridge Received traditional education- Aristotelian Exposed to different ways of explaining nature Chose to read works by Gassendi and Descartes outside of school Deep interest in mechanical perspective Unsure about which version is the best- Descartes or Gassendi No answers seem plausible to him Professor of Mathematics at Cambridge Teachings focused on light and color Published “A new theory about light and colors” in Philosophical Transactions Asked how we should understand light and color Newton sets up 2 glass prisms, and makes a rainbow with light What causes us to see color? Crucial experiment- meant to be a crossroads; makes it possible to propose many mechanical explanations for any phenomenon Descartes’ explanation: what we see as light is transmitted pressure; small, fast-moving matter creates pressure that is transmitted to our eyes when light hits a transparent material (glass/water), the light changes in pressure this change creates “pressure waves” we see as a rainbow Newton’s explanation says if Descartes is right, every time light goes through a prism, it will be changed in pressure Newton sets up 2 prisms, thinking the rainbow will change through the second prism the red and purple rays are the same A light ray will stay the same color no matter how many times you send it through a prism Light consists of moving corpuscles (bodies of matter) corpuscles are sent through space from the sun the prism changes the speed of the corpuscles the ones that are slow look purple; the ones that are fast look red by the second prism, the fast/slow corpuscles have already been sorted, so the color stays the same This experiment showed that mechanical explanation was wrong Newton gets criticized We can “make the model fit” Newton is sorting the rays according to speed, but maybe it’s a question of size The larger corpuscles could be red, the smaller ones could be purple Newton’s reaction/strategy in responding The experiment shows us something about the nature of light and color We see that light has certain properties Color-Red light always looks red Refraction- red light bent a little, violet is bent more Only wants to describe the behavior of what we see Does NOT try to explain why the behaviors are the way they are Skeptical Crisis Relation Newton can’t pick which explanation is the best Did Newton care about what was real? – YES Newton “backs off” from the mechanical philosophy; goes into seclusion Newton and Gravity Emmett Halle convinces Newton to publish his work on celestial motion (Mathematical Principles of Natural Philosophy 1687) Newton tried writing his ideas, and published a different version later In the draft version, Newton asks what the ancients thought about celestial motion They noticed it was circular Decline started with Aristotle/predecessors What did Aristotle do wrong? Thought celestial objects were made of aether, being carried around be aether Explaining the behavior of celestial motion is where the ancients went wrong Newton doesn’t like the physical explanations Newton liked Tycho, but didn’t like Keplar’s magnetism or Descartes’ vortexes Newton didn’t want others to easily understand his book; thought their “prejudices” would prevent them from being interested People who want mechanical explanations would be disappointed Newton decided to limit his audience Re-writes his book in a mathematical style Writes in the form of proofs Limits it to those who can follow his mathematical reasoning If people can follow his reasoning, they will understand he is only giving descriptions What does Newton write about? The paths the planets take Things continue to move unless something makes them change How much centripetal force (center-seeking) force does it take to keep something moving in a circle? relationship between force and speed relationship between force and distance develops mathematical descriptions about the relationships of force, speed, etc. he discovers that his formula is universal- GRAVITY (“heavy”) What causes Gravity? Newton doesn’t answer this question Christiaan Huygens- “can’t accept the core of what Newton is doing” Huygene likes Descartes, and doesn’t like Newton’s disagreement Newton has given a universal force, but can’t explain its cause Newton is shifting from explanation to description- why? Had to do with his religious beliefs Newton was secretive about his religious views The Opticks About light and color At the end, Newton lists queries (asks questions) In the queries, Newton shows what he believes about God He thought God created atoms that interacted by collision He didn’t think motion was constant motion is decreasing (friction, etc.) the world will eventually stop moving there must be another source of motion active principles- source for keeping/adding motion divine omnipotence- decisions by something/somebody to add more motion (God is playing a role in the cosmos) if there was only a mechanical cosmos, everything would stop, but God can add motion Newton says God has the power to intervene in motion- controversial Conflicts with God’s divine omniscience (being all-knowing) Gottfried Wilhelm Leibniz Engages Newton in debate about God Newton’s god has to “wind up the clock” and add motion; didn’t agree Newton asks what kind of God Leibniz imagines Where do we see God working as part of the world? He can’t “start the clock ticking” and do nothing What kind of respect can we give God unless he has divine power?