Friday, April 30, 2010
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7:09 AM
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Though Newton had earlier tried to develop a Descartes mechanical physics, his major physics work seems to have involved combining laws of force and motion in mechanics with a Gilbert-like attraction theory, to develop laws of gravitational orbital motion around 'centres of force'. Newton saw gravity as governing the motions of the celestial bodies as well as of apples falling from trees. He used the 'force' terminology perhaps more readily associated with Galileo-Descartes mechanics AND the 'attraction' terminology associated often with William Gilbert attraction theory, and allowed that gravity might be due to unseen signals acting across empty space in line with Gilbert's theory OR might be caused by the impact force of unseen ether particles in line with Descartes theory.
Hence, in the Principia final Scholium to Book 1 Section 11, after showing that planet orbits can be explained by some centripetal force directed towards the sun, Newton concludes that the existence of gravity as a property of bodies can be deduced from the proven existance of magnetism as a property of bodies ;
"These propositions naturally lead us to the analogy there is between centripetal forces, and the central bodies to which those forces used to be directed ; for it is reasonable to suppose that forces that are directed to bodies should depend on the nature and quantity of those bodies, as we see they do in magnetical experiments."
Also in this scholium Newton states that he is not committing to any particular manner of operation of 'at-a-distance' forces or of 'contact' forces.
"I here use the word attraction in general for any endeavour, of what kind soever, made by bodies to approach each other ; whether (as Gilbert) that endeavour arise from the action of the bodies themselves as tending mutually to or agitating each other by spirits emitted ; or whether (as Descartes etc) it arises from the action of the aether or of the air or of any medium whatsoever whether corporeal or incorporeal any how impelling bodies placed therin towards each other. In the same sense I use the word impulse, not defining in this treatise the species or physical qualities of forces but investigating the quantities and mathematical proportions of them"
Clearly to Newton bodies moved, but experiment could not decide if they were actually moving themselves or were being pushed by others - there is no evidence to decide between active matter and dead matter or between 'A moves B', and 'B moves itself in response to A'.
Of course this was not accepted by many physicists (who Newton noted in Principia's introduction to Book 3, had "prejudices to which they had been many years accustomed"), and it was too difficult for Einstein or anyone else to address. But Newton saw his laws of science as correctly predicting natural events without needing to know why things happened, in the manner of 'black box' behaviour laws that relate only inputs or stimuli to outputs or responses without considering any mechanisms connecting them. Newton considered hypotheses regarding currently unseens as matters of philosophy or logic and not science, and not disprovable by science. Newton concluded that though he had disproven substantial elements of Galileo-Descartes mechanical physics, like ether vortex motion gravity and motion tides, some modification of a mechanical ether theory might correctly explain gravity, magnetism, electricity and light. But Newton himself seemingly prefered to use Gilbert-style attraction theory in thinking about physics, which he also thought might perhaps correctly explain gravity.
Newton's considerations on Descartes push-physics as against Gilbert response attraction physics is maybe best put in his Principia Book 3 Rule 3. Here he first shows how we can reason that matter has solidity and exclusive-space-occupancy Then how "we must universally allow that all bodies whatsoever are endowed with a principle of mutual gravitation." Then he concludes that the argument is stronger for the universal gravitation of all bodies than for their impenetrability. But in finding that Gilbert-like physics was somewhat more likely the true option, Newton concluded that the evidence did not exist to decide between the two theories and might well never exist, continuing with "In bodies we see only their figures and colours, we hear only the sounds, we touch only their outward surfaces, we smell only the smells, and taste the savours : but their inward substances are not to be known either by our senses or by any reflex act of our minds" - Newton could see no evidence for Descartes 'certain knowledge'.
Newton also did useful work on light and sound, and produced a theory of fluids that solved problems of fluids in movement and of motion through fluids. This he applied to Descartes' supposed unseen universal fluid ether, in which many physicists came to believe, but Newton disproved substantial aspects of that and never conceded any kind of mediating ethers or signals as proven entities though granting that action-at-a-diatance needed some kind of mediation. He did in his 'Opticks' and elsewhere use both ether explanation and attraction explanation to help clarify his new physics ideas, especially for physicists who supported either one of such explanations and their 'unseens'. Many at the time saw Newton as developing Gilbert's theory which Galileo-Descartes supporters had made very unpopular by name-calling only, but one of Newton's great originalities was in his seeing particular explanations as unnecessary to science and hypotheses on unseens as being unscientific - and being the first clear proponent of a blackbox science simply predicting everything. Copernicus, Galileo and others had earlier done some black-box science, but excluded explanation only either as being more politic or as to be perhaps done later.
Mathematics was also advanced by Newton's work on calculus, which many of his peers falsely claimed was stolen from Leibnitz. But his science was presentationally mathematical and distinctly in the style of Euclid, though Newton always required that experimental facts must be decisive in science and not mere logical deduction or mathematics alone.
Newton was the chief proponent of defined mathematical behaviour laws with undefined-explanation 'black box science', maybe chiefly because he could see no way to decide between the alternative Gilbert and Descartes physics explanations ('Newton's Dilemma') or between alternative explanations of light. If different theories could fit the same mathematics then they were either really the same theory or were compatible image theories and descriptions that only appeared different. Newton did convince a few other scientists of his time into favouring black box physics that could predict everything without relying on explanations, as being the best physics possible as long as there were no proven physics theories without unseens. But explanation-theory retained its popularity among scientists and was even credited to Newton ironically. Black box theory was maybe fine while nature was seen as being relatively simple, but it perhaps looked less intelligible when nature became seen as being more complex - so it could be argued that defined explanation is then needed to help make a theory more understandable ? Or maybe some correct science theory cannot be understandable to many anyway ? Of course a science theory cannot be only a bare mathematics with no physical meaning, but it can be a mathematics whose physical meaning is not fully uniquely defined.
Newton knew how badly Gilbert's earlier physics theory had been treated, and correctly expected that his theory partly based on it would likely be equally badly received. He tried publishing one short paper on a part of his optics work submitted in 1672 to the Royal Society. Newton's first paper in 1672 was only a small correct non-theory technical paper on colours, colour abberation and Newton's new reflecting telescope - fully proving all that it said. But amazingly the eminent scientist peer Robert Hooke immediately tried to stop the Royal Society publishing this first paper of Newton, and himself published a ridiculous criticism of it. In response to Newton amplyfying/defending his light ideas in December 1675 an angry Robert Hooke threatened to form his own Royal Society. Yet most science historians expect people to believe that it was Newton who was unreasonable ! See Newton 1672. Then in 1684 Gottfried Leibniz began publishing some of Newton's key mathematics as his own and by 1690 many were claiming that Newton had stolen Leibniz maths. Newton decided against publishing further papers, and though he held a higher opinion of some earlier thinkers like Eucld, he was very wary of putting his ideas to most of his peers. With a few minor mostly anonamous exceptions and private letters to a few friends, Newton waited until he could publish his science himself complete in book form - his Principia in 1687 and his Opticks in 1704. And when they were very badly received by largely Descartes-supporter peers of whom Newton held a low opinion, Newton finished with science. Attraction physics was rubbished as being anthropomorphic, with silly claims that it required all matter to have eyes, minds and legs - ridiculous claims that themselves involve anthropomorphic thinking. (Gravity being simple can clearly need only the simplest response, and the relative nature of attraction theory really gave it more scientific power.) And Newton's blackbox theory was soon simply ignored as though it did not exist.
To quote 'A Short Account of the History of Mathematics' (4th edition, 1908) by W. W. Rouse Ball, on Newton, from www.maths.tcd.ie -
" His theory of colours and his deductions from his optical experiments were at first attacked with considerable vehemence. The correspondence which this entailed on Newton occupied nearly all his leisure in the years 1672 to 1675, and proved extremely distasteful to him. Writing on December 9, 1675, he says, `I was so persecuted with discussions arising out of my theory of light, that I blamed my own imprudence for parting with so substantial a blessing as my quiet to run after a shadow.' Again, on November 18, 1676, he observes, `I see I have made myself a slave to philosophy; but if I get rid of Mr.Linus's business, I will resolutely bid adieu to it eternally, excepting what I do for my private satisfaction, or leave to come out after me; for I see a man must either resolve to put out nothing new, or to become a slave to defend it.' "
A majority of Newton's peers were strong Descartes physics supporters who would not consider alternative theories, and especially would not consider the old enemy Gilbert attraction theory. They saw Newton as an anti-Descartes Gilbert theorist and belived that Newton's blackbox position was a just a fraudulent cover to disguise his backing for the hated Gilbert theory. The minority of Newton's peers who would reasonably consider alternative theory ideas, mostly took Newton at face value as supporting blackbox theory and not attraction theory - and only few of them accepted black box theory. Nobody other than Newton gave any real consideration to attraction theory, not even to attempt disproofs of it. And Newton himself produced no disproofs of it, only disproofs of parts of Descartes mechanical physics which suffered from more rigid requirements as do many other physics theories. Newton firmly held to his blackbox-science line dividing scientific knowledge from non-scientific knowledge - with religion and explanations of gravity both being areas of great interest outside science. (Newton privately tried unsuccessfully to develop his physics to fit with his religious ideas, and to develop its effluvia/spirits and chemistry. But his religious ideas were much more specific and detailed than those of Descartes, his attraction theory ideas were less precise than those of Gilbert and chemistry was to need so much more experimenting that it was still being called alchemy.)
Newton like Gilbert became acclaimed as a great scientist, while the theories of both were rejected without disproof (much later Einstein did produce his 'disproof' of Newton which was eagerly accepted with nobody looking closely at exactly what theory was supposedly being disproved). The failure of Gilbert and Newton theory among physicists was not reflected among non-physicists, and even today most people see their signal attraction theory as correctly explaining magnetism and gravity. A caricature of part of Newton's physics theory became acclaimed somewhat slowly, with his real theory rejected with Gilbert's by the mob of scientific pigmy peers - and that process continues still now. Or maybe, being really generous, it could be said that the world was just not ready to look at a physics that was not some single mechanical push physics - and maybe the world is still not ready ?!
For comparison with other physics theories, Newtons three laws of motion were ;
1. Every body will remain at rest, or in a uniform state of motion unless acted upon by a force.
2. When a force acts upon a body, it imparts an acceleration proportional to the force and inversely proportional to the mass of the body and in the direction of the force.
3. Every action has an equal and opposite reaction.
Newton's view of 'a force acting' allowed of either some kind of Descartes 'dead-matter' push action or Gilbert 'robot-matter' signal attraction action.
For an overview of a 'Gilbert-Newton' view of gravity see The Attraction Theory of gravity and other forces.
MOTIONS.
The chief evidence of the operation of most physical laws of nature is found in different motions, as considered in the studies of many concerning physics such as Galileo, Gilbert, Kepler, Descartes, Newton and Einstein.
The perseverance of much natural motion like planet orbits and spins suggests to some space offering no resistance to, and having no effect on, motion - though not to Einstein.
The perseverance of natural planet orbits seems to require the force of gravity, but natural spins seem like rest and uniform straight line motion in requiring no force to maintain them.
Another basic type of natural motion is reflection, as where the path of motion of something moving is changed when it meets another object - eg when a moving ball meets a wall or when a light ray meets a mirror. One possible explanation of some or all reflections is contact collision, of two things being unable to occupy the same space so that the parts of any motions directed to occupying the same space have their direction reversed. A second possible explanation of some or all reflections is proximity repulsion, where things increasingly repel each other as the distance between them narrows. And interestingly for light reflection Newton suggested the further possible explanation of 'post-contact' proximity attraction, where a surface strongly attracts something passing it in close proximity.
Motions common in larger visible objects may also be common in less easily seen microscopic objects - or may not. Hence microscopic objects do commonly show one apparantly random motion called Brownian motion which may or may not have a real equivalent in larger object motion. And there is always the issue of the absoluteness and the relativity of any motion
Posted by
M.Hamza Ali
Labels:
Theories
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