Читать книгу Isaac Newton: The Last Sorcerer - Michael White - Страница 7

If God created the world, where was he before the Creation? … Know that the world is uncreated, as time itself is, without beginning and end. Mahapurana (India, ninth century)

What is matter, and how does it move? These are questions that have occupied the thoughts of physicists from ancient times to the present day, and they were fundamental queries for Isaac Newton.

Our modern view is based upon the rather exotic world of quantum theory, but for most everyday purposes the way in which we manipulate matter and energy relies upon rules and systems discovered between Newton’s lifetime and the present century. For many historians of science, Newton’s ideas about how matter behaves and how energies and forces operate can be seen as a watershed in the development of physics. Indeed, some perceive his work as making possible the Industrial Revolution. Newton provided a focus: he was an individual scientist who drew together the many threads that led from ancient times to his fathering of modern empirical science (a study based upon mathematical analysis as well as experimental evidence). Behind Newton lay some 2,000 years of changing ideas about the nature of the universe; his great achievement was to clarify and to bring together the individual breakthroughs of men like Galileo, Descartes and Kepler and to produce a general overview – a set of laws and rules that has given modern physics a definite structure.

The ancient Greeks were the first to record their ideas about the nature of matter, and we know of several different schools of reasoning. The two most important for our purposes are the teachings of Aristotle and the ideas of a rival theory – the atomic hypothesis of Democritus.

The Greek philosophy that prevailed up to Newton’s time was that traditionally attributed to Aristotle – the notion of the four elements: earth, water, air and fire. The alternative was the ideas of Democritus, born some seventy-five years before Aristotle, in 460 BC, who taught that matter is made up of tiny invisible parts, or atoms. Because Aristotle and Plato both largely disapproved of Democritus’s atomic theory, however, it was almost completely ignored from Aristotle’s day until its partial revival during the seventeenth century.

The first person to formulate the idea of the four elements was actually a Sicilian philosopher named Empedocles, some half-century before Aristotle’s birth, but the idea was refined and made popular by Aristotle. It is thought that the concept first arose from watching the action of burning. For example, when green wood is burned, the fire is visible by its own light, the smoke vanishes into air, water boils from the wood, and the remaining ashes are clearly earth-like. This gave rise to the idea that everything in the universe is composed of different proportions of these four fundamental elements – an idea which became the foundation of Aristotle’s work in natural philosophy that was handed down to future generations.

Aristotle was born in 384 BC at Stagira in Chalcidice. The son of the physician to Philip, King of Macedon, he later became the pupil of Plato and, in middle age, the teacher of Alexander the Great. He wrote a collection of tracts that were not only influential in his own time but whose rediscovery in an incomplete form by European scholars during the thirteenth century heralded a return to learning and the earliest emergence of the Renaissance. Those most relevant to his thoughts on natural philosophy (what by the eighteenth century had become known as physics) were On Generation and Corruption and Physical Discourse, which concentrated upon ideas concerning matter, form, motion, time and the heavenly and earthly realms.

To Aristotle, the earthly realm was composed of a blend of the four elements which, if left to settle, would form layers: water falling through air (or air moving up through water, as do bubbles), solid earth falling through water and air, and fire existing in the top layer because it moves up through air. Using this model, Aristotle would have explained the fall of an apple as being due to the earthy and watery parts of the solid apple trying to find their natural place in the universe, falling through air to reach the ground. As well as popularising the idea of the four elements, Aristotle also pioneered the concept of the Unmoved Mover – the name he gave to the omnipotent being who maintained the movement of the heavens, keeping the Sun and the planets travelling around the Earth.

Aristotle’s work was encyclopedic in range, and he wrote on almost all subjects known at the time, covering logic, philosophy, biology, astronomy and physics. His strongest subjects were logic and, of the sciences, biology; his weakest was physics. Most significant for how Aristotle arrived at many of his scientific ideas was his creation of syllogistic logic: the principle that a conclusion can be reached as a logical consequence of two preceding premisses. An example of this is the collection of statements ‘All elephants are animals; all animals are living things; therefore all elephants are living things.’

Syllogisms are powerful tools in the study of logic, and were used as a fundamental mathematical procedure until the nineteenth century, when they were superseded by more versatile ideas, but their use is a rather superficial way to conduct science, because syllogistic logic does not contain an element of experiment: syllogisms consist merely of two statements and a conclusion based upon superficial observation or deductive reasoning.

Plato, Aristotle’s teacher (and the man who established the school at the Academy in Athens which lasted nine centuries), actively disliked experiment and so it was never established as a guiding principle for Greek natural philosophy. Instead, Aristotle and the generations of Greek thinkers who followed him created a rigid set of rules based upon syllogistic logic only, producing a distorted picture of reality. But, because of Aristotle’s stature, this limited approach became endowed with an aura of infallibility which persisted until the beginning of the modern era. The historian Charles Singer has said of this unfortunate process:

The whole theory of science was so interpreted, and the whole of logic was so constructed, as to lead up to the ideal of demonstrative science [i.e. conclusions reached through reasoning alone], which in its turn rested on a false analogy which assimilated it to the dialectics of proof. Does not this mistake go far to account for the neglect of experience and the unprogressiveness of science for nearly 2,000 years after Aristotle?¹

In the same vein, the writer and historian Sir William Dampier pointed out that:

Aristotle, while dealing skilfully with the theory of the passage from particular instances to general propositions, in practice often failed lamentably. Taking the available facts, he would rush at once to the wildest generalisations. Naturally he failed. Enough facts were not available, and there was no adequate scientific background into which they could be fitted.²

The modern scientific method involves reasoning and experiment. To give a simple example: early on in a scientific investigation an idea is postulated – often based upon an inspired insight. This is then developed into a tentative hypothesis by means of pure reasoning – a process called the inductive method. The practical consequences of this hypothesis must then be deduced mathematically and the idea is tested experimentally. If there are discrepancies between the hypothesis and the experimental results or observations, the hypothesis must be altered and the experiments be repeated until there is either agreement between reasoning and observation or the original idea is discarded. If the reasoning and the practical verification eventually agree, the hypothesis is promoted to the status of a theory. This can then be used to attempt to explain a more generalised scenario than the original concept and may hold for many years. But, crucially, it is still never considered to be the only theory that could fit the facts, and good science allows for new ideas to be introduced that may destroy the old theory or demand radical changes.^*

Aristotle’s dominance left no room for alternative ideas. Democritus, the father of the atomic theory, believed that ‘According to convention there is a sweet and a bitter, a hot and a cold, and according to convention there is colour. In truth there are atoms and void.’ Aristotle dismissed this notion by relying upon syllogisms that were founded upon inadequate knowledge. For example, he claimed that, if the atomic theory were true, matter would be heavy by nature and nothing would be light enough in itself to rise. A large mass of air or fire would then be heavier than a small mass of earth or water, so the earth or water would not sink (or the air and fire rise) and therefore the elements would not find their natural positions. This argument illustrates how Aristotle was not approaching the problem in the way a modern objective scientist would – he was not able to consider questioning his own cherished beliefs even when presented with a strong alternative theory.

Aristotle’s dogma became almost a religion among his followers, and his teachings were passed on to future generations virtually unquestioned, misguiding future thinkers and leading science along a partially blind alley for several hundred years without interruption.

By the time of Aristotle’s death, in 322 BC, the Egyptian city of Alexandria was about to emerge as the intellectual centre of the world. At its heart was the great library which is said to have contained all human knowledge in an estimated 400,000 volumes and scrolls. From Alexandria, learning spread eastward with the conquests of Alexander the Great and west into Europe, where Greek philosophy, science and literature acted as the foundation for Roman culture. This was especially true of science: the Roman era could boast many great intellects – Pliny, who lived during the first century AD and wrote a thirty-seven-volume treatise, Naturalis Historia, and Plutarch, a thinker of the following generation, to name only two. But these men did little original science and concentrated on refining and clarifying Greek teachings passed on to them.

Of the Greek science that survived through to the early Roman era, the work of Aristotle, Plato, Archimedes and Pythagoras was best preserved, although the ideas of Democritus were championed by the Roman philosopher Lucretius in his poem De Natura Rerum. By the time Roman power was melting away and the library at Alexandria was decimated at the hands of the Christian bishop Theophilus around AD 390 (it was later sacked a second time by the Arabs during the seventh century), Aristotle’s work was becoming unfashionable.

The reason for this lies in a shift from pure intellectual inquiry to a distrust of any learning beyond theological exegesis: this plunged most of civilisation into what has become known as the Dark Ages. In this era, as the Roman Empire was in rapid decline, education and learning became dominated by religious fanaticism. The disciples of this new movement, the Stoics, believed in the supreme importance of pure spirit over material existence and therefore shunned learning about the physical world as an end in itself. To them, Aristotle’s work was too mechanistic, too embedded in physical reality.^* Instead, the musings of Plato held much greater relevance and were perfectly in tune with the new obsession with religious meaning.

Plato had taught an anthropocentric view of reality in which everything was created and carefully controlled by a supreme being who held the interests of humanity paramount. For Plato, the movements of the planets were there simply to enable the marking of time, and he viewed the cosmos as a living organism with a body, a soul and reason. He also saw numerical relevance and meaning in all natural processes, and because of this he placed great importance upon mathematics. However, he abhorred experimental science, which, according to one historian, he ‘roundly condemned as either impious or a base mechanical art’.³

There is no clear point at which the Dark Ages ended in Europe. Learning in some form had been kept alive in the monasteries, but the interest of the Christian fathers had lain in mysticism and religious relevance rather than practical or theoretical science. The Arabs, who had made great strides in the understanding of alchemy, mathematics and astronomy throughout the period, maintained an interest in pure science, and as this knowledge filtered gradually into Europe the shadow of ignorance lifted. But it was a slow process, taking three or four hundred years.

Sometime between 1200 and 1225, Aristotle’s works, which had been saved in part by the Arabs and amalgamated with their own ideas, were rediscovered by European intellectuals and translated into Latin. From this point on, Aristotle’s science returned to favour and took over from Platonic mysticism, gradually fusing with Christian theology.

Although this development may be viewed as an improvement upon the Dark Age mistrust of science and the Stoics’ preoccupation with spirituality, it created a new obsession – a marriage of Aristotelian natural philosophy with Christian dogma. This meant that any attack upon Aristotle’s science was also seen as an attack upon Christianity. Together, the two doctrines formed a powerful alliance and created a world-view that was taught by rote almost unchallenged in every university in Europe for almost half a millennium, from the thirteenth to the seventeenth century.

These twinned beliefs produced a self-contained picture of the universe: God created the world as described in the Scriptures and guided all actions. All movement was not only set in motion by God but was supervised by divine power. The Church’s doctrine of divine omnipotence thus dovetailed perfectly with Aristotle’s belief in the Unmoved Mover – that no movement was possible unless initiated by an unseen hand. All matter consisted of the four elements and was not divisible into atoms as Democritus had proposed. To Aristotle, every material object was an individual complete entity, created by God and composed of a particular combination of the four elements. Each object possessed certain distinct and observable qualities, such as heaviness, colour, smell, coolness. These were seen as solely intrinsic aspects or properties of the object, and their observed nature had nothing to do with the perception of the observer.

To the thirteenth-century mind, the notion that properties of an object such as smell, taste or texture were partly open to interpretation in the mind of the observer would have been totally alien. Every property of an object was intrinsic and the same for all observers. Furthermore, because Aristotle had rejected atomism, the concept that matter was composed of tiny, indivisible elements would have been equally foreign to most people of the time. And, because Aristotelian ideas were now bound up inextricably with religion, any philosopher who openly challenged any aspect of accepted scientific ideology put his life in danger.

Yet, despite the severe limitations this placed upon the development of scientific inquiry, the Middle Ages did produce a collection of notable and original thinkers who contributed to a gradual reawakening of rationality. Together, these men led the way to the Renaissance and the full flowering of innovative science that followed.

Still wrapped up in the need to marry natural philosophy with theology, the thinkers of this period – who became known as the Scholastics, the most famous of whom were St Thomas Aquinas and Albertus Magnus – stuck to the traditional Aristotelian line, shunning experiment. However, they did champion the search for truth outside the limited realm of pure theology. Although they maintained a firm belief that man was the central object of Creation and that the universe was designed for man by God, they had progressed to the idea that the study of Nature and the physical world could lead to greater theological enlightenment. It was not until the deaths of Aquinas and Albertus Magnus (towards the end of the thirteenth century, some seventy-five years after Aristotle had been reintroduced into Europe) that the work of the great Oxford scholar Roger Bacon began to erode the restrictions of Scholasticism.

In some ways Bacon was a man born ahead of his time. Although he subscribed to many traditional beliefs of the Scholastics, he was the first to see the usefulness of experiment and he composed three far-sighted tracts – Opus Majus, Opus Minor and Opus Tertium – which outline his philosophy and his experimental techniques in a range of disciplines. This effort established Bacon’s reputation for posterity, but did little for him during his lifetime. Viewing his work as anti-Establishment and its anti-Aristotelian elements as subversive, Jerome of Ascoli, General of the Franciscans (later Pope Nicholas IV), imprisoned him for life as a heretic.

The scientific renaissance that followed Bacon’s time marks a change in philosophical beliefs every bit as significant as that in the arts. Men such as Leonardo da Vinci, who approached science from a practical standpoint, foreshadowed many of the ideas of Galileo, Kepler and Newton, but did not write up their discoveries in any coherent form. The best we have is Leonardo’s collection of notebooks, which indicate his studies and philosophies. In one sense, Leonardo was all experiment and represented the opposite extreme to the Greeks.

Leonardo held an opposing view of motion to Aristotle. Aristotle claimed that nothing moved unless it was made to do so by God, the Unmoved Mover. Leonardo suggests the exact opposite, writing in his notebook, ‘Nothing perceptible by the senses is able to move itself … every body has a weight in the direction of the movement.’⁴ In other words, matter has an innate tendency to move in a certain direction unless stopped. This anticipates the notion of inertia first postulated by Galileo some half-century later and eventually formalised by Newton.

Galileo, who was born in 1564 (about forty years after Leonardo’s death), is regarded by historians of science as the greatest thinker in the realm of motion and matter up to Newton’s time. It is generally agreed that his practical demonstrations paved the way for Newton’s own blend of experimental verification and mathematical integrity.

Galileo’s work in this area was revolutionary because he was the first to devise repeatable experiments that showed that Aristotle’s ideas were quite wrong. He is probably most famous for his use of the telescope, which destroyed the traditional ideas of how the solar system is constructed (see Chapter 4), but equally important for the progress of science was his work in what became known as the science of dynamics.

Aristotle held that bodies were either intrinsically light or heavy and they fell at different velocities because of their innate tendency to seek their natural places. In 1590 the Flemish philosopher Simon Stevin had shown that light and heavy objects falling through a vacuum reach the ground simultaneously. Galileo repeated this experiment the following year (although probably not from the Leaning Tower of Pisa as tradition had it) using a cannonball and a musket-ball and showed that the two fall at equal speed if the resistance of air is ignored.

More importantly, Galileo suspected from this experiment that a falling body moves with a speed proportional to the time it has been falling. But, because the balls fall too quickly for the eye to measure their actual speed, he could not formulate a mathematical relationship between the speed of descent and the time it took. In order to find this relationship, he needed to conduct an experiment in which the speed of descent could be measured.

He quickly established that, ignoring friction, an object rolling down an inclined plane acquires the same speed as it would if it was falling vertically through the same distance. This enabled him to construct a series of experiments in which he let balls roll along inclined planes and measured the time of their journey and their speeds. This confirmed that the speed of a falling object does indeed increase with the time of the fall.

In a variation on this experiment, he allowed a ball to roll down an inclined plane and roll up another. In a further test, he allowed the ball to travel on beyond the slope along a horizontal path, where it continued steadily until slowed and eventually stopped by friction.

It was these experiments that convinced Galileo that Aristotle’s idea of the Unmoved Mover was false. Objects do not move because they are constantly being pushed or pulled: rather, they possess inertia – an innate tendency to move unless stopped.

This was a revolutionary notion, but his views on other questions concerning matter and energy also entitle Galileo to be seen as the first of the modernists. He rejected Aristotle’s idea of the four elements and subscribed to Democritus’s atomic theory at least three decades before it began to make a reappearance in the schemes of Europe’s leading thinkers, though he was unable to prove it. He also flew in the face of Aristotle’s insistence that objects possess integrally all the properties we sense when we observe them, declaring:

I feel myself impelled by necessity, as soon as I conceive a piece of matter or corporal substance, of conceiving that in its nature it is bounded and figured by such and such a figure, that in relation to others it is large or small, that it is in this or that place, in this or that time, that it is in motion or remains at rest, that it touches or does not touch another body, that it is single, few or many; in short by no imagination can a body be separated from such conditions. But that it must be white or red, bitter or sweet, sounding or mute, of a pleasant or unpleasant odour, I do not perceive my mind forced to acknowledge it accompanied by such conditions; so if the senses were not the escorts perhaps the reason or the imagination by itself would never have arrived at them. Hence I think that those tastes, odours, colours etc. on the side of the object in which they exist, are nothing else but mere names, but hold their residence solely in the sensitive body; so that if the animal were moved, every such quality would be abolished and annihilated.⁵

So, contrary to Aristotle, Galileo states categorically that there are two distinct qualities of bodies. The first may be considered primary qualities, which are inseparable from and fundamental to the nature of the object in question – what twentieth-century scientists would ascribe to the atomic structure and chemical nature of an object. The others are secondary qualities, which are interpreted by the senses of the observer.

These revolutionary notions of Galileo’s – ideas which have perhaps been swamped by his more famous discoveries in astronomy and dynamics – greatly influenced the French philosopher René Descartes, who for a time informed Newton’s thinking on the subject of matter and the nature of the physical universe.

Descartes is most famous today for two developments – Cartesian coordinates, which still play a key role in mathematics, and dualism, a philosophy which proposes a sharp distinction between body and soul, matter and spirit. According to Cartesian dualism, the spirit is personal and nebulous, and matter must therefore be impersonal and concrete.

In Descartes’s image of the universe, matter is immersed in an unseen, immeasurable medium called the ether. God endowed the universe with movement at the beginning of time and allows it to run spontaneously but in accordance with his will. Because in this scheme matter fills all of space, there can be no such phenomenon as a vacuum and all motion is produced by matter impressing on other matter within the medium of the ether. Descartes expressed this in his famous theory of vortices, in which he pictured movement, such as the fall of a stone to the earth, as being like the movement of a feather or a straw caught in an eddy or a whirlpool.

Descartes rejected mysticism and the occult in his writings and visualised the universe as a machine. Every action involving matter was purely mechanistic, and matter had no contact with spirit. To Descartes, all animals – including humans – were also mere machines. Humans had a spiritual aspect, a soul, but this had no link with our physical selves.

These ideas were highly controversial. On a scientific level, Descartes’s concepts were unverifiable and he did not contrive experiments to support his theories. On a superficial level, his vortex theory did not clash with the doctrines of Galileo, in that it did not contradict experimental evidence. Galileo had shown that, because of inertia, all movement continued until stopped, and Descartes proposed that the universe had been set in motion by God. The two ideas were not incompatible: if we assume the Creator set things in motion, they would continue until stopped by, say, the intervention of mortals.

But the most radical aspect of Cartesian philosophy was that it implied to many that, once the universe had been set in motion, God was no longer needed. The Creator had been effectively demoted from ‘Supreme Good’ to ‘First Cause’. Naturally this was a view hotly disputed by theologians and the majority of philosophers, many of whom had been brought up on Aristotle and still thought along the same lines as the Scholastics of the thirteenth century.

Descartes died when Newton was eight years old, but his philosophies were becoming immensely fashionable as Newton entered university and extended his reading beyond the curriculum. Because it contained material referring to his disputed theories of divine function in a mechanical universe, Descartes’s most famous book, Discourse on the Method (published in 1637), was unpopular with the ecclesiastical authorities, but his theories were discussed openly in the more liberal universities of Europe and began to spread.

As Descartes’s theories of dualism became known, three other philosophers were helping to create the intellectual scene to which Newton would add his own unique ideas.

Pierre Gassendi, who was a Catholic priest and a close contemporary of Descartes, revived the work of Democritus and proposed an atomic theory in which matter was composed of tiny indivisible parts. Unlike Descartes, Gassendi did not attempt to describe a mechanistic universe in which all action on a fundamental level occurred by way of vortices – a theory which for many people marginalised God. Instead, he envisaged a universe composed of Democritus’s atoms presided over by an all-pervading Creator. Gassendi’s outlook has been dubbed ‘Christianised atomism’, because it maintains an omnipotent and omnipresent role for God. This was more acceptable than Descartes’s model to men like Newton, who sought a mechanistic model for the universe but could not countenance any diminishing of the Creator’s position.

Another great innovator of the time was Robert Boyle, today seen as the supreme experimentalist of his era. Boyle believed in practical analysis and was more concerned with how a phenomenon occurred rather than why it happened.

Boyle tried to unite elements of Descartes’s philosophy of a mechanistic universe with the revived atomic theory, but he did not subscribe to the contention that God had no role in the physical world after initiating primal movement. Like Gassendi, he held that God’s ‘general concourse’ was continually needed to keep the mechanical universe working. But a greater contribution to the study of matter and energy was his demonstration of the fallacy of Aristotle’s notion of the four elements.

In one of these displays, Boyle illustrated how fire could not be considered a basic element and that Aristotle’s claim that fire could resolve things into their elements was false. He demonstrated that, contrary to Aristotle’s belief, gold can withstand fire and can also be alloyed with other metals and then recovered in its original form, suggesting the existence of unalterable ‘corpuscles’ of gold. He also showed that even when fire did break down materials it required different degrees of heat and different time periods to succeed, and more often than not it produced new substances that were also complex. Finally, he showed that some materials could not be reduced by fire alone.

The last of the major seventeenth-century figures who greatly influenced Newton’s intellectual development was Francis Bacon. Bacon was not solely a philosopher. He was Lord Chancellor under James I, and was an essayist and moral philosopher who wrote widely about the way he thought science should be conducted. In his The Advancement of Learning (1605), The New Organon (1620) and especially The New Atlantis (1627), he criticised the blind pursuit of Aristotelian philosophy and the rote-learning system of the universities. And, most importantly, he was the first to formulate what has become known as the experimental or inductive method. It was Bacon who, some time before Descartes dismissed magic and superstition, argued that scientific discipline should be guided and inspired by religious motivations. In The Advancement of Learning he wrote:

To conclude therefore, let no man out of weak deceit of sobriety, or an ill-applied moderation, think or maintain, that a man can search far or be too well studied in the book of God’s word, or in the book of God’s works; divinity or philosophy; but rather let men endeavour an endless progress or proficiency in both.⁶

Although he would have agreed with Descartes’s dismissal of metaphysics, Bacon objected to scientific ideas being driven purely by philosophy and the deductive reasoning employed by Aristotle, which Descartes did not completely shake off. In effect, Bacon was the first to conceive of a ‘Christian Technocracy’. Quoting Daniel in the Old Testament, that ‘many shall run to and fro, and knowledge shall be increased’, he envisaged a science driven by religion, guided by strict logical rules and experimental verification (almost as modern scientists perceive it) and aimed at enlightenment and practical applicability. Although Cartesianism provided Newton with a platform of reasoning about a mechanical philosophy which in turn led to the Industrial Revolution, it was Bacon’s scientific method, which was readily adopted by generations of natural philosophers, including Newton, that provided the modus operandi for the Scientific Revolution.

So, by the middle of the seventeenth century, as Newton was preparing to enter the academic world, natural philosophy was in a state of flux. The old notions of Aristotle still provided the traditional backbone of university study in the areas of logic, astronomy and natural philosophy, but this was primarily because of an old school of influential academics. Gradually, radical ideas from the Continent were eroding the Greek philosopher’s supreme position. According to one historian of science, ‘From being a realm of substances in qualitative and teleological relations, the world of nature had definitely become a realm of bodies moving mechanically in space and time.’⁷

It was within this climate of change that Newton entered university in 1661 and took the first steps towards finding his own path through the shifting philosophies of the time and establishing his own views.