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Thomas Young’s Bakerian lecture.

 The Implications of His Double-Slit Experiment.
_______________
Undulationists v. Corpuscularists.

By CHRISTINE SIMON.

 

1.

Thos. YoungTHE ROYAL SOCIETY’S Bakerian lecture for 1803 was given on 24 November by Thomas Young and was entitled ‘Experiments and Calculations Relative to Physical Optics’. In it, Young described an experiment he had conducted ‘on the fringes of colours accompanying shadows’.1 This apparently innocuous experiment not only reignited the debate on the nature of light, unleashing a torrent of impassioned criticism, but prefigured one of the strangest developments in modern physics.

Young made a small hole in a window shutter and placed over this a piece of thick paper which he had pierced with a fine needle. Light passing thus through a small gap diverges into a cone; into this small ‘cone of diverging light’ Young placed ‘a slip of card, about one-thirtieth of an inch in breadth’ (approximately 0.85 mm) and observed its shadow, both on the opposite wall and on ‘other cards held at different distances’ in the beam of light. On each side of the shadow made by the card were fringes of colours. The shadow itself was ‘divided by similar parallel fringes […] differing in number, according to the distance at which the shadow was observed, but leaving the middle of the shadow always white’.2

youngslitswikidotThe patterns Young was here observing were caused by diffraction; this is ‘the slight spreading of a light beam into a pattern of light and dark bands when it passes through a narrow slit or past the edge of an obstruction’.3 He correctly inferred from these results that light was acting as a wave – diffraction and interference patterns are exhibitions of wave behaviour – and gave the first section of this lecture the heading ‘Experimental Demonstration of the General Law of the Interference of Light’.

In his Letters to a German Princess, written between 1760 and 1762, Leonhard Euler had asked of the sun’s light, ‘What are these rays? That is, beyond question, one of the most important inquiries in physics.’4 The nature of light was still unresolved by the time Young performed his experiment. There were two alternatives: either light was a stream of particles, or corpuscles as Newton had called them, or it was a wave. Many scientists held strong views on the subject, the two camps being divided along roughly national lines.5 In his Opticks, Newton had suggested that light was a stream of tiny particles emitted from the light source like miniature bullets. This particle hypothesis carried the weight of his authority and was championed by the majority of British scientists. On the continent, however, most followed Huygens and Euler in favouring the wave theory.

At the time of Young’s experiment, neither hypothesis could give a totally convincing account of the observed phenomena of light. The particle hypothesis seemed to offer a better explanation of propagation in straight lines, and reflection could be adequately explained by both hypotheses; the wave hypothesis, however, provided a more satisfactory explanation for refraction, diffraction and the phenomenon we now call Newton’s rings. (These are a set of concentric coloured rings observed when a slightly convex lens is placed on a flat glass plate, thus creating a gap of varying depth, and illuminated from above by a beam of white light.) Newton’s explanation of refraction had it that light must travel faster in water than in air, although the opposite would be expected now since water is the denser medium. Diffraction, he said, was the effect of rays of light – composed of corpuscles – ‘in passing by the edges and sides of bodies, [being] bent several times backward and forwards, with a motion like that of an eel. And do not the three fringes of colored [sic] light […] arise from three such bendings?’6 Although with hindsight these ideas appear somewhat bizarre, the evidence available at the time was far from conclusive. And to complicate matters, Newton himself, in the ‘Queries’ of the Opticks, had allowed for the possibility of light as a wave. His use of the corpuscular model to explain two phenomena – Newton’s rings and the combined reflection and refraction of light from a surface such as water – involved particles which existed in different states, or ‘fits’: ‘fits of easy reflection’ and ‘fits of easy transmission’. However, to explain these fits, Newton made use of a wave concept.7

Young: ‘I am of opinion that light is probably the undulation of an elastic medium’.

The embryo of Young’s ideas on light can be seen in a paper written in January 1800, entitled ‘Sound and Light’. Although this paper deals principally with sound, sections X and XI refer to light. Much of the debate on light at this time made use of an analogy with sound, which was known to propagate itself as a wave. This was initially a fruitful analogy, but caused problems later on because sound and light are different types of wave. A wave may be defined as a transfer of energy ‘from one point to another without any particle of the medium being permanently displaced; particles merely oscillate about their equilibrium positions’.8 Sound is a longitudinal wave: a wave in which the motion of the particles is in line with the direction of propagation of the wave. Light, on the other hand, is a transverse wave, in which the motion of the particles is at right angles to the direction of propagation.9 In Section X of his ‘Sound and Light’ paper, entitled ‘The analogy between light and sound’, Young states the problems caused by the Newtonian (particle) hypothesis: it does not provide an explanation for the uniform velocity of light or for combined reflection and refraction; nor does it explain the phenomenon of Newton’s rings. Section XI of the paper deals with the interference of sound waves; and, although Young stops short of suggesting that these phenomena of light may also be explained by the interference of waves, the juxtaposition was perhaps fruitful. What is certain is that by the next year, when he wrote on the subject in Nicholson’s Journal, he was a cautious undulationist, writing ‘I am of opinion that light is probably the undulation of an elastic medium’. In this article he notes that the wave theory explains as well as the particle theory the observed phenomena of light, and in fact provides a better explanation for two of them: diffraction and ‘all the phenomena of the colours of thin plates’ (such as Newton’s rings).10

By November 1801, in his paper ‘On the Theory of Light and Colours’, which introduced his ideas on three-colour vision, Young is already discussing the interference of light waves, although he does not use the word ‘interference’ itself. He approaches this by analogy with sound waves, and describes the effect as observed in water waves. (In 1802 he was to demonstrate this interference effect in a ripple tank, a piece of apparatus he had invented.)11

The concept of interference explained the colours seen in Newton’s rings without the contrived and awkward explanations put forward by Newton. Young (correctly) deduced that the colours of the rings were a result of the constructive interference of specific wavelengths of light, the other wavelengths (colours) being eliminated by destructive interference. (Constructive interference occurs when the waves are ‘in phase’, i.e. when the crests and troughs of the waves coincide, thus intensifying their effect. Destructive interference occurs when the waves are ‘out of phase’: the crest of one wave coincides with the trough of another and the waves thus cancel each other out.) Young even went further and calculated the wavelengths of the seven basic spectral colours. However, the evidence he presented in his 1801 paper was not enough to convince those who still believed in Newton’s less elegant but still influential hypothesis.

Young believed that his paper of November 1803, ‘Experiments and Calculations Relative to Physical Optics’ provided clinching evidence for the wave theory of light, beginning it with the following words: ‘I have found so simple and so demonstrative a proof of the general law of the interference of two portions of light […] that I think it right to lay before the Royal Society, a short statement of the facts which appear to me so decisive.’12 Since diffraction is a property of waves and not of particles, the diffraction fringes he had observed could only be caused if light were a wave.

2.

HOWEVER, YOUNG’S EXPERIMENTS were the subject of three vituperative attacks in the newly-launched Edinburgh Review. Two of these appeared in January 1803: one on his paper ‘On the Theory of Light and Colours’ (read to the Royal Society in 1801 and published in the Philosophical Transactions in 1802) and another on a second paper by Young on the same subject, published in the same volume of the Transactions. The third review appeared in 1804 and dealt with Young’s 1803 paper ‘Experiments and Calculations Relative to Physical Optics’. Although all three reviews were anonymous, Young correctly identified the reviewer as Henry Brougham.

Brougham’s criticism is of interest not just for its arguments, but for the insights it gives into the scientific culture of the day. His first review, aggressive from the start, accuses Young’s work of being unscientific and retrograde:

But we have of late observed in the physical world a most unaccountable predilection for vague hypothesis daily gaining ground; and we are mortified to see, that the Royal Society, forgetful of those improvements in science to which it owes its origin, and neglecting the precepts of its most illustrious members, is now, by the publication of such papers, giving the countenance of its high authority to dangerous relaxations in the principles of physical logic. We wish to raise our feeble voice against innovations, that can have no other effect than to check the progress of science, and renew all those wild phantoms of the imagination which Bacon and Newton put to flight from her temple. We wish to recal [sic] philosophers to the strict and severe methods of investigation pointed out by the transcendant [sic] talents of those illustrious men, and consecrated by their astonishing success.13

henrybroughamBrougham is here expressing a valid concern for the integrity of science, significantly invoking the authority of two of its most important British proponents. But in his subsequent criticism of Young’s competence as a scientist, he makes an interesting but spurious distinction between what he considers to be valid and invalid scientific practice. Taking Young to task for having revised his ideas on a couple of topics (the crystalline lens of the eye and the colours caused by refraction in ‘mixed plates’), Brougham draws a distinction between ‘a discovery in mathematics, or a successful induction of facts’, which should be published immediately, and ‘an hypothesis’, which is ‘a work of fancy, useless in science, and fit only for the amusement of a vacant hour; […] as it requires continual polishing, touching, and retouching, in order to adapt it to the phenomena’.14 Significantly, Newton (in the ‘General Scholium’ of the second edition of the Principia) had written, ‘Non fingo hypotheses,’ or ‘I do not make hypotheses’. This was a response to a criticism of the first edition of the Principia, that gravity – which is invisible and acts over huge distances – was an occult force. Newton’s argument here was that since the cause of gravity was not apparent, it would be improper to speculate on it. He draws a distinction between acceptable and unacceptable scientific procedures. Science (‘natural philosophy’) – he writes – proceeds through ‘particular propositions […] inferr’d from the phænomena, and afterwards render’d general by induction’; hypotheses, ‘whether metaphysical or physical, whether of occult qualities or mechanical, have no place in experimental philosophy’.15 And in the Opticks he wrote, ‘My design in this book is not to explain the propositions of light by hypotheses, but to propose and prove them by reason and experiments.’16 This is not entirely true of his own practice, but there are in fact two issues here. The first has to do with a central principle of scientific practice: the effort to free it from speculative assumptions. The second is semantic: the word ‘hypothesis’, according to the OED, has two senses: first, ‘a proposition […] stated (without any reference to its correspondence with fact) merely as a basis for reasoning or argument’; and second

a supposition put forth to account for known facts; esp. in the sciences, a provisional supposition from which to draw conclusions that shall be in accordance with known facts, and which serves as a starting-point for further investigation by which it may be proved or disproved and the true theory arrived at.

Newton.Newton uses the word ‘hypothesis’ in the first sense (he defines it as ‘whatever is not deduc’d from the phænomena’). However, as both Young and his biographer Peacock subsequently pointed out, science – unlike mathematics – proceeds by the successive refining of hypotheses (in the second sense) rather than by the discovery of hard-and-fast ‘truth’. (A similar confusion between a general and a scientific usage exists today around the word ‘theory’. In order to remove the possible connotations of conjecture and speculation from the phrase ‘theory of evolution’, Richard Dawkins coins the word ‘theorum’ to denote ‘a hypothesis that has been confirmed or established by observation or experiment’.)17 Brougham also assumes that scientists first do experiments which show them the ‘truth’; whereas in fact it is more usual for experiments to be devised in order to test a hypothesis, which is then confirmed, modified or abandoned in the light of the evidence.18

Although in his second review Brougham is less offensive (but no less critical), he reverts to invective in his third, which appeared in volume 5 of the Edinburgh Review in October 1804. He writes of Young’s law of interference as ‘one of the most incomprehensible suppositions that we remember to have met with in the history of human hypotheses’. Young’s paper contained ‘more fancies, more blunders, more unfounded hypotheses, more gratuitous fictions, all upon the same field on which Newton trod, all from the fertile, yet fruitless, brain of the same eternal Dr Young.’19 This exaltation of Newton as possibly infallible is reminiscent of that of Aristotle in the two millennia before the scientific revolution. Aristotle’s ideas concerning the physical world – originally consistent with observed data – became so codified into an all-encompassing doctrine, ratified by the Church, that it was difficult to disagree with it even long after conflicting observational evidence had been gathered.

There was a conceptual difficulty that many scientists found unacceptable: how could two rays of light combine to produce darkness?

Young’s hypothesis was correct, yet there were several factors which prevented its being taken entirely seriously. In the first place the experiment itself, with its slips of card held up in a beam of light, was somewhat clumsy. And although the card used was very thin, it was not thin enough to produce the most obvious diffraction patterns. There was also a conceptual difficulty that many scientists found unacceptable: how could two rays of light combine to produce darkness? In addition, although from his experiment on Newton’s rings Young had made careful measurements and calculated the wavelengths of monochromatic light, his other experiments lacked quantitative data. The experiment on interference ‘lacked the kind of precision and mathematical rigor [sic] increasingly expected by physicists.’20

3.

YOUNG ANSWERED BROUGHAM’S criticisms in a pamphlet published in November 1804: ‘Reply to the Animadversions of the Edinburgh Reviewers’, a measured response which largely confined itself to a discussion of the scientific issues raised by Brougham, such as the function of hypothesis and theory in science.21 However, although he maintained an interest in the subject of light, keeping abreast of new developments and writing an article on it for the Encyclopaedia Britannica,22 he abandoned his experiments, turning to other areas of study (such as the deciphering of the Rosetta stone) and building up his medical practice. He also decided that any future publications on scientific matters, except medical ones, would be anonymous. This is generally considered to be a result of the distress occasioned by Brougham’s criticisms, and there is no doubt that this was a major influencing factor. At the same time, however, Young’s abandonment of light was not entirely out of character. He did have a tendency to flit from one subject to another; not without doing useful work, but without the same degree of focus as someone whose interests were less encyclopaedic, or whose income depended on achievements within one professional field.

What is certain is that his work on interference was all but forgotten; it was rarely referred to between 1804 and 1816. Only with the more mathematical work of Arago and Fresnel in the next decade of the nineteenth century was convincing evidence obtained for the wave theory. From 1808 new experiments were performed and by the 1820s most scientists had been won over. Much of this work centred on the phenomenon of polarization. Young had continued to follow developments in optics, writing reviews of others’ work and discussing ideas in his correspondence. In a letter to Arago in 1817 he suggested an explanation of polarization by positing that light might be a longitudinal wave with a small transverse component. Fresnel learnt of this idea from Arago and also developed Young’s earlier work on interference and diffraction. Fresnel’s work, which was underpinned with rigorous mathematics, showed by 1821 that light is in fact a wave, but a transverse one, and explained virtually all the phenomena of light in terms of the wave theory.23

Many histories of science take it as read that Young’s experiment, although it met with some incredulity and hostility in the first instance, ‘proved’ the nature of light, and that scientific truth progressed smoothly from one concept to the next. John Gribbin, for example, states that ‘the progress of science was not held up because similar evidence in support of the wave model came almost immediately from (perhaps appropriately) Britain’s bitterest foe at the time, France’.24 Although in the long term this was the case, it was almost twenty years before the work of Fresnel established the wave theory, and the actual process was often one of bitter conflict. The row between Young and Brougham was echoed in a similar disagreement between Arago (an undulationist) and Biot (a corpuscularist) in 1822 over the polarization of light. Peacock comments that ‘Arago attacked the rival theory of Biot […] with so much vehemence both of language and argument, that the friendship between them […] was permanently dissolved.’25 In an effect similar to that of Brougham’s earlier criticism of Young, this enmity obscured the work carried out by Fresnel – work which was crucial to the establishment of the wave theory.

That theory did gain ground, however. Fizeau showed in 1850 that the speed of light is slower in water than in air, thus providing further evidence against the corpuscular theory, which had predicted the opposite.26 And the work of James Clerk Maxwell in the 1860s was conclusive. Maxwell unified the theories of electricity and magnetism and showed that light is a form of electromagnetic radiation. It was impossible, he wrote, ‘to avoid the inference that light consists in the transverse undulations of the same medium which is the cause of electric and magnetic phenomena.’27

4.

Running through Brougham’s reviews is a contrast between the scientific hero Newton and the upstart Young.

RUNNING THROUGH BROUGHAM’S reviews is a contrast between the scientific hero Newton and the upstart Young who had dared to tread on the hallowed ‘field on which Newton trod’. Brougham was perhaps irked by the fact that the experiment reported in Young’s 1803 paper, in which light is passed through a shutter, was reminiscent of Newton’s classic experiment with the prism. And the title of Young’s 1801 paper, ‘On the Theory of Light and Colours’, echoed that of Newton’s 1672 paper, ‘A Letter of Mr. Isaac Newton […]; containing his New Theory about Light and Colors [sic]’.28 (In Pope’s famous epitaph the whole of Newton’s work is encapsulated in an image of ‘enlightenment’: ‘Nature and Nature’s Laws lay hid in Night./GOD said, Let Newton be! and all was Light.’)29 Newton’s authority did carry considerable weight, despite the fact that his ideas on the nature of light were not conclusive. By the time of Young’s experiments, Britain was at war with France and there was an added element of patriotism in supporting Newton’s particle hypothesis over what was seen as the ‘continental’ undulatory idea.30 (Nationalistic concerns were to play a similar part in resistance to Einstein’s ideas during the Great War; Eddington – a pacifist Quaker – was one of the few in Britain to take Einstein’s work seriously.)

However, Brougham’s attitude to Newton’s authority is contradictory. He drops the names of Newton and other scientific heavyweights of the past into his reviews, in a way which is probably meant to be intimidating. On the one hand, he accuses Young of using Newton to give weight to his own theories, pointing out the importance of Newton’s status:

Those who are attached, as all may be with the greatest justice, to every doctrine which is stamped with Newtonian approbation, will probably be disposed to bestow on these considerations so much the more of their attention, as they appear to coincide more nearly with Newton’s own opinions.31

Yet later, when accusing Young of twisting Newton’s ideas to bolster his own, Brougham denies the weight of authority in science at all:

We are far from meaning to admit the criterion of authority appealed to by our author. We hold the highest authority to be of no weight whatever in the court of Reason; and we view the attempt to shelter this puny theory under the sanction of great names, as a desperate effort in its defence, and a most unwarrantable appeal to popular prejudice.32

This issue of authority is a significant one in science, but Brougham’s criticisms of Young also have a personal element, which perhaps explains their exaggerated nature. It is likely that Brougham bore a grudge against Young as a result of events which had taken place some years earlier. Young had reviewed a mathematical paper by Brougham published in the Philosophical Transactions in 1798. Significantly, he had criticized Brougham for the fact that he had ‘proceeded too far in animadverting on the writings of Newton, Barrow, and other eminent mathematicians’.33 Peacock saw a link between Young’s earlier criticism of Brougham and the latter’s scathing comments in 1803 and 1804:

Though [… Young’s] particular criticism referred to was just, it was somewhat flippant and ungracious, and was probably not without its influence in provoking the severe retaliatory treatment which Young’s own Memoirs [papers] shortly afterwards experienced at the hands of one who, not himself invulnerable, was armed at all points, and always prepared to come to close quarters with his enemies.34

We perceive here a hint of Brougham’s character; this belligerence was to stand him in good stead in his career as a radical lawyer. In fact, though Brougham does not come well out of this disagreement with Young, he was later to gain a reputation as an eloquent friend and protector of radicals against government repression. He defended John and Leigh Hunt on more than one occasion for libels in their weekly Examiner, most famously at their trial in December 1812 for libel against the Prince Regent (which resulted nonetheless in two years’ imprisonment for each defendant).35

In fact Brougham and Young had crossed swords even earlier: in 1795 Brougham had criticized Young’s first Royal Society paper. Added to this was Brougham’s disappointment that, despite the support of one of the secretaries of the Society, Sir Charles Blagden, he had failed to realize his ambition of entry into the Society until well after Young was elected. ‘It seems only too probable,’ comments Robinson, ‘that Brougham perceived the polymathic Young to be a scientific rival, whom he envied – a Mozart to his Salieri.’36

5.

THIS EPISODE REVEALS some interesting details about the nature of scientific practice in the early nineteenth century. The fact that both Brougham and Young had other forms of employment was not at all anomalous. Unlike today, this was an age when educated amateurs could not only understand the latest scientific debates, but could – and often did – make significant contributions themselves.

In Brougham’s reviews we also catch a glimpse of the conflict between the Royal Society and the Royal Institution. Young, as well as being foreign secretary of the Royal Society, was professor of natural philosophy at the Royal Institution, an establishment about which Brougham is scathing:

We demand if the world of science, which Newton once illuminated, is to be as changeable in its modes, as the world of taste, which is directed by the nod of a silly woman, or a pampered fop? Has the Royal Society degraded its publications into bulletins of new and fashionable theories for the ladies, who attend the Royal Institution? Proh pudor! Let the professor continue to amuse his audience with an endless variety of such harmless trifles; but, in the name of Science, let them not find admittance into that venerable repository, which contains the words of Newton, and Boyle, and Cavendish, and Maskelyne, and Herschell [sic].’37

PneumaticksThere was some concern about the Royal Institution and its aim of popularizing science. Many scientists of the day saw the Institution less as a scientific establishment than as a place of fashionable entertainment (it welcomed ‘ladies’); it was certainly considered inferior to the Royal Society. Gillray’s cartoon of a lecture at the Royal Institution (‘Scientific researches! New discoveries in PNEUMATICKS! – or – an Experimental Lecture on the Powers of Air’) captures the raucous and farcical atmosphere which its detractors considered to be the norm at the Institution.38 Brougham states a concern for the scientific honour of the Royal Society; he is unhappy that ‘paltry and unsubstantial’ papers are slipping in which are unworthy of the Society’s prestige, and worries that this is causing a decline in its reputation; he implores it to vet its papers more thoroughly, so as to ‘cease to give its countenance to such vain theories as those which we find mingled, in this volume [the Society’s Transactions], with a vast body of important information.’39

6.

YOUNG IS ALSO celebrated for a second experiment, described in his monumental digest of scientific thought, A Course of Lectures on Natural Philosophy and the Mechanical Arts, published in 1807. This is his ‘double slit experiment’, in which a beam of homogeneous (single-colour) light is passed through two very small slits in a screen and the resulting pattern observed on a ‘surface placed so as to intercept them’.40 This pattern is an alternation of dark and light bands, similar to that obtained from the earlier experiment with the slips of card. In this experiment the two beams of light passing through the two slits interfere with each other, the light bands on the screen occurring as a result of constructive interference and the dark bands as a result of destructive interference.

Although this experiment, like its predecessor, provides convincing evidence for the wave theory of light and is often considered to be Young’s coup de grâce in the establishment of that theory, there is no definitive evidence that he actually performed it. Historians of science are divided on the matter.41 The experiment was not submitted to the Royal Society and the only written account of it is tucked away in the Course of Lectures. One historian, Nahum Kipnis, believes that Young did perform the experiment but with the slits too far apart to obtain interference patterns.42 (In this case, he would have observed diffraction patterns, as in the earlier single-slit experiment. However, since diffraction is also an exhibition of wave behaviour, this would not alter the conclusion that light is behaving as a wave.)

That this experiment may have been a thought-experiment gives it a curious resonance with a later, even more famous, one. In Richard Feynman’s double-slit experiment (originally a thought experiment, although it was later performed, giving the results he had predicted) electrons, rather than a beam of light, are fired through the two slits. Since electrons are sub-atomic particles, they would be expected to behave as particles and accumulate in two heaps opposite each of the slits. In fact, something very strange happens: on the screen appears an interference pattern similar to that obtained in Young’s double-slit experiment. In other words, the electrons are behaving as waves.43 It may be inferred from this that electrons have both wave and particle properties. The same results are obtained when photons (particles of light) are used. And in fact, this wave/particle duality, or complementarity, extends not just to electrons and light but to all objects. Ask wave questions and you get wave answers; ask particle questions and you get particle answers.44 Like one of those black and white pictures which reveal an old hag or a beautiful young woman depending on how you look at it, reality is characterized by an inherent ambiguity.

Also at the heart of the quantum world is uncertainty. Although in the electron double-slit experiment the final pattern is always the same, it is impossible to predict the behaviour of any single electron. The individual motions of the particles are unpredictable. It is possible to predict the behaviour of large numbers of particles (what may be called the ‘statistical model’) but not that of individual ones (the ‘dynamic model’). Heisenberg’s uncertainty principle states that it is impossible to know simultaneously the position and the momentum of a particle (such as an electron). This is not to do with any inadequacy of equipment or of experimental methods, but is an inherent property of nature.45

But that is not the only strange outcome of the double-slit experiment. The same result (i.e. an interference pattern, the result of wave-behaviour) is obtained even if only one electron is released at a time. This would suggest that somehow each electron passes through both slits.46 However, if the experiment is set up in such a way that individual electrons are ‘observed’ (detected) as they pass through the slits, it is found that each electron passes through either one slit or the other, and the interference pattern disappears. What appears on the screen in this case is the pattern of distribution which would be obtained if, for example, bullets were being fired.47 The act of observation changes the outcome, since it introduces energy into the experiment which changes the state of the object.48 ‘The observer interacts with the system [the experimental apparatus] to such an extent that the system cannot be thought of as having independent existence.’49

Because the macro world consists of atoms whose component particles behave according to quantum rules, it follows that all material reality is in some sense underpinned by the strange concepts of quantum theory.

Despite the fact that for the behaviour of objects on the everyday level, the uncertainty involved is minute and therefore insignificant, these results have radical implications for our understanding of nature. Because the macro world consists of atoms whose component particles behave according to quantum rules, it follows that all material reality is in some sense underpinned by the strange concepts of quantum theory.50

Many scientific developments have come about only after a battle with what appears to be self-evident. That the earth is hurtling round the sun at approximately 30 kilometres per second is not obvious; nor is the fact that what we understand as solid matter is composed of minute particles which themselves consist largely of empty space. But the discoveries of quantum theory defy not only what we think of as ‘common sense’ but much of what we have come to understand as ‘reasonable’. Although scientists are comfortable with its technological applications (many of which are now indispensable to modern life, such as lasers and the electronics of the computer, the mobile phone, the programmable washing machine and so on) many would admit that even they themselves cannot comprehend the realities behind quantum theory.51 In contrast to the early years of the nineteenth century, our own age is characterized both by an increasing specialization in all areas of knowledge and by a reconditeness in science which makes much of it difficult to access. This is in part a result of the mathematicization of science. It is interesting that Zajonc sees the division between scientists and non-scientists – between those who understand the mathematics and those who do not – as being in existence as early as 1773, the date of Euler’s confrontation with Diderot at the court of Catherine the Great in St Petersburg. The great philosophe was incapable of answering Euler’s ‘proof’ of the existence of God, since it was expressed in the form of an equation.52

But the difficulty of science as exemplified in wave-particle complementarity does not exonerate us from the responsibility of trying to understand it. Science is, after all, an explanation of the way the material world works. Non-scientists may have to make do with a purely linguistic expression, with what Maxwell called ‘the tenuity and paleness of a symbolic [i.e. analogic] expression’; but even Maxwell conceded that ‘scientific truth’ could be expressed by such means.53


Christine Simon was born in Salford and read French at King’s College London, subsequently becoming a secondary-school teacher. Since then she has undertaken a variety of jobs, including library work and teaching IT at HMP Styal. In 2011 she completed a PhD in creative writing, for which she wrote a historical novel; set during the time of the French Revolution, it uses the wave-particle complementarity of light as a metaphor to examine the ambiguities of the historical period and the life of the double agent. She is currently a visiting lecturer at the University of Chester.

NOTES:

  1. Thomas Young, ‘The Bakerian Lecture. Experiments and Calculations relative to physical Optics’, Philosophical Transactions of the Royal Society, 94, 1 (January 1, 1804), (accessed 09/12/09) (p. 1).
  2. Young, ‘The Bakerian Lecture’, p. 2.
  3. The Hutchinson Encyclopedia of Science, ed. by Sharon Brimblecombe, Diana Gallannaugh and Catherine Thompson (Oxford: Helicon, 1998), pp. 226-27.
  4. Quoted in Arthur Zajonc, Catching the Light: The Entwined History of Light and Mind (Oxford: Oxford University Press, 1995), p. 99.
  5. The OED dates the first recorded use of the word ‘scientist’ to 1834, and it was still not in wide use in 1840. I have nonetheless used this word throughout in preference to the historically accurate but cumbersome ‘natural philosopher’ – a term which in any case appears only to have been used of gentlemen.
  6. Quoted in Robinson, The Last Man, pp. 101-02.
  7. Robinson, The Last Man, pp. 99-101.
  8. Chambers Science and Technology Dictionary, ed. by Peter M. B. Walker (Edinburgh: Chambers, 1988), p. 963.
  9. Walker, Chambers Science and Technology Dictionary, pp. 533, 920.
  10. George Peacock, Life of Thomas Young, M.D., F.R.S., &c., and One of the Eight Foreign Associates of the National Institute of France (London: John Murray, 1855), p. 131.
  11. Robinson, The Last Man, p. 107.
  12. Young, ‘The Bakerian Lecture’, p. 1.
  13. Henry Brougham, ‘The Bakerian Lecture on the Theory of Light and Colours. By Thomas Young, M.D. F.R.S.’, Edinburgh Review, 1 (1803), 450-456 (pp. 450-51).
  14. Brougham, ‘The Bakerian Lecture’, p. 451.
  15. The General Scholium to Isaac Newton’s Principia Mathematica’, trans. by Andrew Motte, The Newton Project Canada (2004), (accessed 07/12/09) (para. 5 of 6). (Newton never himself published an English edition of his great work.)
  16. Quoted in Joel Levy, Newton’s Notebook: The Life, Times and Discoveries of Sir Isaac Newton (Stroud: The History Press, 2009), p. 128.
  17. Richard Dawkins, The Greatest Show on Earth: The Evidence for Evolution (London: Bantam, 2009), pp. 9-13.
  18. Robinson, The Last Man, p. 117.
  19. Quoted in Robinson, The Last Man, p. 116.
  20. Robinson, The Last Man, p. 170. (OED dates the use of the word ‘physicist’ in this sense to 1840.)
  21. Robinson, The Last Man, p. 116.
  22. Robinson, The Last Man, p. 171.
  23. Robinson, The Last Man, p. 170.
  24. John Gribbin, Science: A History: 1543-2001 (London: Allen Lane, 2002), p. 406.
  25. Peacock, Life of Thomas Young, p. 387.
  26. Gribbin, Science, p. 425.
  27. Quoted in Cyril Domb, ‘James Clerk Maxwell’, Encyclopædia Britannica.
  28. The Newton Project, University of Sussex, (accessed 29/10/09).
  29. ‘Intended for Sir Isaac Newton, in Westminster-Abbey’, in Pope: Poetical Works, ed. by Herbert Davis (London: Oxford University Press, 1966), p. 651.
  30. John Gribbin, In Search of Schrödinger’s Cat (London: Black Swan, 1991), p. 17.
  31. Brougham, ‘The Bakerian Lecture’, p. 453.
  32. Brougham, ‘The Bakerian Lecture’, p. 454.
  33. This remark was made by Dr Robison of Edinburgh in the Philosophical Transactions (1800) in response to a paper by Young which criticized Robert Smith’s ‘Treatise on Harmonics’. Peacock, Life of Thomas Young, p. 129.
  34. Peacock, Life of Thomas Young, p. 130.
  35. Nicholas Roe, Fiery Heart: The First Life of Leigh Hunt (London: Pimlico, 2005), pp. 175-81.
  36. Robinson, The Last Man, pp. 118-19.
  37. Brougham, ‘The Bakerian Lecture’, p. 452.
  38. Robinson, The Last Man, p. 92.
  39. Henry Brougham, ‘An Account of some Cases of the Production of Colours not hitherto described. By Thomas Young, M.D. &c.’, Edinburgh Review, 1 (1803), 457-460 (p. 459).
  40. Quoted in Robinson, The Last Man, p. 122.
  41. Robinson, The Last Man, pp. 123-24.
  42. Robinson, The Last Man, p. 124.
  43. See Goronwy Tudor Jones and Alan Wall, ‘The Most Beautiful Experiment’ in Alan Wall, Myth, Metaphor and Science (Chester: Chester Academic Press, 2009), pp. 89-92.
  44. Jones and Wall, ‘The Most Beautiful Experiment’, p. 89.
  45. Gribbin, Schrödinger’s Cat, pp. 119-20.
  46. Gribbin, Schrödinger’s Cat, pp. 170-71.
  47. Jones and Wall, ‘The Most Beautiful Experiment’, p. 94.
  48. Jones and Wall, ‘The Most Beautiful Experiment’, p. 96.
  49. Gribbin, Schrödinger’s Cat, p. 160.
  50. Gribbin, Schrödinger’s Cat, pp. 146-47.
  51. Gribbin, Schrödinger’s Cat, ch. 7.
  52. Zajonc, Catching the Light, p. 113.
  53. Quoted in Gribbin, Science, pp. 429-30.

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