Uncertainty Einstein, Heisenberg, Bohr, And the Struggle for the Soul of Science by David Lindley;...

7/30/2019 Uncertainty Einstein, Heisenberg, Bohr, And the Struggle for the Soul of Science by David Lindley; Richard a Blasb

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Book Review

UNCERTAINTY: EINSTEIN,HEISENBERG, BOHR, AND THESTRUGGLE FOR THE SOUL OFSCIENCE BY DAVID LINDLEYReviewed by Richard A. Blasband, M.D.

I f you are mathematically challenged, as am 1, but still wish to understand howquantum mechanics and the uncertainty principle came about, as am 1, then thisslim, wonderfully written volume is for you. David Lindley, an astrophysicist,science journal editor, and author of several books on various aspects of the historyof science, has given us here an extremely well written, well referenced andannotated history of the development of scientific thinking beginning with RobertBrown's discovery of what came to be called "Brownian motion" in plant seeds andending with Werner Heisenberg's discovery of the uncertainty principle in modernphysics. Along the way he wittingly and perceptively tells us of the main players inthis quest to understand how nature works, of their triumphs, foibles, and theirbattles with each other over the "soul" of physics, that is whether nature is contin-uous in its changes from one state to another and thoroughly deterministic orwhether it is discontinuous and probabilistic. Anyone interested in science will findUncertainty wonderfully informative and a magnificent read. In this review I haveparaphrased and borrowed extensively from Lindley with the intention of presentinghis view as accurately as possible.The story begins with the Scottish physician and clergyman, Robert Brown, who in1827, saw through a microscope that pollen grains of the wildflower, Clarkia Pulchella,endlessly jiggled about although there was no obvious reason why they should do so.Interestingly, the plant was named by its discoverer, Meriweather Lewis, in 1806 forhis co-discoverer of the Northwest Passage, William Clarke. Make of this possiblysynchronistic pairing of the two discoveries what you will. Who knew?

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In the early 1800s the atomic theory whichhad been extant since Democritus andLeucippus first propounded it in 400 BC,was in flux. Atoms as the cause of how thingsworked was believed by some scientists,doubted by others. In 1863, however,Ludwig Christian Weiner, described how themovement of atoms could readily accountfor Brownian motion, which, within anothercouple of decades was observed in anymaterial of sufficiently small size in solution.However, calculations indicated that themovement of atoms of the solution washundreds of times faster than what was beingobserved in the "jiggling" of the microscopicparticles. The apparent solution to thepuzzle came with the formulation at the endof the 1800s by Louis-Georges Douey of astatistical understanding of atomicmovement: it is the mean impact of atomson the particles that results in their jiggle.While not formulated as such at the time,however, Douey's view was to become athorn in the side of the thoroughly deterministic view of nature that had beenpropounded since the work of Isaac Newton.The Scottish physicist, Clerk Maxwell,"arguably the most eminent theorist of thenineteenth century," believed that if theBrownian particles were submitted to amore powerful microscope they would settleinto a repose: the apparently spontaneousnuisance would go away. The Marquis deLaplace, one of the leading eighteenthcentury developers of Newtonianism,declared that, in essence, if we knew all theforces that animate nature, nothing wouldbe uncertain and all would be predictable.On the other hand most physicists knew

that it would be absurd to think that onecould calculate the individual behavior ofevery atom or molecule in a volume of gas.Statistical descriptions were obviouslyessential. Later the Austrian physicist,Ludwig Boltzman demonstrated his belief inan atomic theory when he, according toLindley, wrote that, "The observed motionsof very small particles in a gas may be dueto the circumstance that the pressure exertedon their surfaces by the gas is sometimes alittle greater, sometimes a litde smaller",which Lindley took to mean that, "becausea gas is made of atoms, and because theseatoms dance around in an erratic way, asmall particle within the gas will be jostledunpredictably back and forth". Einstein,who allegedly knew nothing of Brownianmotion, undertook calculations to ascertainthe cause of the movement of hypotheticalsuspended particles, thus establishing thefirst quantitative treatment of the bombard-ment of the particles by atoms in thesolution . In 1908 his theory was confirmedby detailed measurement of particles insolution by the physicist, Jean Perrin. Fromthis point on the atomic theory wasaccepted by most physicists and statisticalthinking became an intrinsic aspect ofphysical theorizing.With the introduction of probability theclassical Newtonian hope for perfectibility asexpressed by the mathematician, LaPlace,was seriously challenged.As Lindley states it:

Until this time a theory was a set ofrulesthat accounted for some set of facts .



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Between theory twd experiment thereexisted a direct, exact two-way correspon-dence. But that was no longer the case.Theory now contained elements that thephysicists were sure existed in retz/ity, butwhich they couldn't get at experimentally.For the theorist, tltoms had definiteexistence and had definite positions andspeeds. For the experimenter, atomsexisted only inferentially, and could bedescribed only statistically. A gap hadopened up between what a theory saidwas the foil tInd correct picture of thephysical world and Whtlt an experimentcould in practice reveal of that world.

The discoveries of x-rays by Roentgenin1896 and radium in 1898 by the Curiesgot the objective reality pot to boil, so tospeak, adding considerable challenges to thecomfort zone of scientists, who remainedcommitted to a stable deterministicunIverse. Madame Curie wrote in 1898that "radioactivity is an atomic property"and two years later that, " ... the spontaneityof the radiation is an enigma, a su bject ofprofound astonishment." This put a glitchin the classical operation of cause and effect.And, since radioactivity releases energy,where did the energy come from? Thisproblem was solved chiefly by ErnestRutherford, who, with Frederick Soddy,proposed a theory of the transmutation ofatoms within elements via radioactive decayto account for the multiplicity of radioactive elements. Rutherford found that eachradioactive element had a half-life. But, asLindley states it, "... who is to say whichatoms decay and which do not?" Perhaps,as many physicists thought, there were

internal components to atoms, "sub-atoms,"that caused the atom to disintegrate? It wasat this point that Niels Bohr came onto thescene.

Bohr, initia11y a student of Thomson inCambridge, began to study with Rutherfordin Manchester, England in 19] 2. By thenRutherford, through experimentation withalpha particles had discovered that theinterior of the atom had something thatalpha particles bounced of f of, somethingdense, which he defined as the nucleus ofthe atom. A problem, however was how toconceive of the relationship between whatseemed to be a "cloud" of electrons in theatom and the atom's nucleus. Bohr realizedthat in some way the nucleus of the atomheld the complement of electrons in handby some restraining force imagined by Bohrto be like a ball on a spring, vibrating backand forth. Bohr proposed that the electronscould not vibrate with just any amount ofenergy, but could only carry energy Inmultiples of some basic "quantum."The idea of the quantum had beenproposed ten years previously by Max Plankin 1900 in an attempt to solve certainproblems of emitted radiation. It seemedthat when material bodies emitted energythey radiated it in discrete quanta. The idearemained mysterious, but was in the airwhen Bohr formulated his atomic theory.The quantum atomic theory proved ofalmost instant help in solving the problemof the basis for the frequencies of spectroscopic lines displayed by hydrogen, the"Balmer" series. Now, in Bohr's imagination electrons orbited the nucleus much as



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planets orbit the sun. But, the orbitingelectrons cannot have any energy they like,but must take on only a limited set ofvalues. The model worked beautifully inmany situations, although no one knew whyit worked. Which inspired Rutherford toask of Bohr, "How does an electron decidewith what frequency it is going to vibrateand when it passed from one stationary stateto another? It seems to me that you wouldhave to assume that the electron knowsbeforehand where it is going to stop."Radioactive decay and the electron hoppingfrom one orbit to another were spontaneousevents in the same way. In neither case isthere any special time when the changehappens--it just happens and for noevident reason. There is no known physicalcause.The metaphysical implications of thistheory of spontaneous energy emission werelargely ignored by scientists at the time butsome, such as the theoretical physicist,Arnold Sommerfeld, embraced Bohr'satomic theory and augmented it so well thatmany physicists came to speak of the "BohrSommerfeld" atom. In the meantimeAlbert Einstein had achieved fame in 1905for four seminal papers on physics includinga paper on relativity and one where heargued that Plank's argument about littlepackets of energy should be treated at facevalue, as if they were bona fide discrete littleobjects. By applying standard statisticalmethods many of the established propertiesof electromagnetic radiation were readilydemonstrated. By asserting that light was"quantized", Einstein was able to explainpreviously puzzling details of the photoelec

tric effect, where voltage is generated bylight striking certain metals. Of course thequantum theory went against Maxwell'sclassical wave theory of the electromagneticfield where waves behaved smoothly,gradually, and seamlessly. Light quanta,however, came and went abruptly withoutapparent cause. As much as Einsteinbelieved in the latter, when it later came toaccepting the notion of spontaneity Innatu re, he vigorously rebelled.In 1918 and 1920, respectively, WolfgangPauli and Werner Heisenberg, both brilliantyoung men, came to Munich to study inthe Department of theoretical physics withArnold Sommerfeld who was attempting tofind some patterns that could be interpretedas quantum rules in the hope of deepeningphysical theory. He put Pauli andHeisenberg to work on it. The BohrSommerfeld atom of those days was, toHeisenberg, a "peculiar mixture ofincomprehensible mumbo-jumbo andempirical success." Heisenberg did not playby the rules. Searching for somethingwholly new, something radical, hedeveloped a theory of the half-quantum toaccount for the spectroscopic anomalies.Developing his formulation further,Heisenberg found that it worked althoughthere was no natural-scientific basis for itsdoing so.At one of Bohr's lectures at a conference inGottingen, Germany; Heisenberg, who wasmeeting Bohr for the first time, asked whatquantum theory meant, what was theunderlying conception, the true physics ofit all? According to Lindley:

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Bohr did not insist on the need forclassical models that could be translatedsystematically into quantum terms.

R a t h e l ~ he told Heisenberg, the point ofmodels was to capture as much as onecould hope to say about atoms, given theinadequacies of the ideas with whichphysicists were fumbling along. "Whenit comes to atoms," Bohr concludedenigmatically, "language can be usedonly as in poetry. The poet, too, is notnearly so concerned with describing foctsas with creating images and establishingmental connectiom. "

Nevertheless Bohr insisted that despite thefact that quantum physics did not followclassical rules, the language of classical physicsremained indispensible. There existed anoverarching idea Bohr called the "correspon-dence principle," which said that thequantum theory of the atom ought toseamlessly match the classical analyses ofatomic behavior, when the latter are knownto work. This was, apparently, easier saidthan done, except in Bohr's mind, whichoperated in a highly intuitive, yet fruitful way.Bohr, steeped in classical wave theory, feltthat the idea of the existence of discretequanta of light to be untenable and with hisstudents he inveighed against it. However,when John Slater, a Harvard graduatevisiting Copenhagen in 1923, told Bohr ofhis idea that a classically derived radiationfield might guide light quanta in theirinteraction with atoms, Bohr got excited.Bohr, Slater, and another student, HendrikKramer, developed the idea and publishedwhat became known as the BKS theory

which described in purely qualitative termsa new kind of radiation field that surroundsatoms, influences their absorption andemission of light, and also transports energybetween them. In addition, electrons werenow to be seen not as orbiting nuclei in theatom, but as "virtual oscillators," each onecorresponding to a particular spectroscopicline. However, contrary to classical physics,in this system energy was not absolutelyconserved because the emission and absorp-tion of energy ran according to rules ofprobability: it can disappear from one placeand reappear somewhere else without theevent being strictly connected by old-fashioned cause and effect. Apparently theradiation field would account for anydiscrepancies in energy balance in the shortrun, although the sums always added up inthe long run. According to Pauli, however,Einstein thought the whole business to be"Quite artificial" and by 1925, experimentsby Compton demonstrated that the BKStheory was false. Despite this, according toLindley, "The BKS proposal marks ... aturning point. Depending on one's interpre-tation of what the theory actually was, it waseither the last gasp of attempts to restquantum theory on some sort of classicalfoundation or else the first proof that allsuch efforts were doomed." What wasconserved from the BKS theory was the useof virtual oscillators as a means to talk abouthow an atom emitted and absorbed light. Itfell to Heisenberg to transform this innova-tion into a wholly new theory of physics.Max Born, the head of the department oftheoretical physics at the university atGottingen, laid the groundwork for



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Heisenberg with a paper caJIing for a newsystem of "quantum mechanics," that is, astructure of quantum rules obeying theirown logic, not necessarily following thedictates of classical, Newtonian mechanics.Born also abandoned the use of traditionalcalculus which was incapable of dealingwith phenomena that were discontinuous,abrupt, and spontaneous. Heisenbergsuggested that the characteristic frequenciesof the proposed oscillators, not the positionand velocity of the electrons, would be thebasic elements of the atomic physics and themotion of electrons would be expressed onlyindirectly. This was revolutionary.Heisenberg developed a new and strangemathematics, which yielded a consistentresult for the energy of a system-but onlyso long as that energy was one of a restrictedset of values. According to Lindley,Heisenberg's new form of mechanics was, infact, a quantized form of mechanics.In the meantime the French physicist, LouisDeBroglie wondered whether Einstein'sparticles of light might display some of theptoperties of waves if they could act in astream of particles. Combining Planck'squantization rule for radiation withEinstein's E=mc 2 for moving objects,DeBroglie proposed that the speed of aparticle yielded a certain wavelength, thefaster the speed, the smaller the wavelength.He then calculated that an electron circlinga nucleus would have a wavelength equal tothe orbit's circumference. For an electronin the next outermost orbit the circumference was twice the electron's wavelength,and so on. In other words, the alJowedorbits of the Bohr atom were those for

which a whole number of electronwavelengths fit around the orbit's circumference.In 1925, influenced by de Broglie'sconcepts, the Viennese physicist IrwinSchrodinger enlarged on de Broglie'selectron wave concept, suggesting thatparticles are not really particles at all, butwere "whitecaps" of an underlying wavefield. An equation described a fieldgoverned by a mathematical operator thatembodied a kind of energy function. Whenapplied to an atom the equation yielded alimited number of solutions in the form ofstatic field patterns, each one representing astate of the atom with some fixed energy.I t was also possible to understand aquantum jump, a transition from one stateto another, not as an abrupt and discontinuous change but as a fluid transformationof one standing wave pattern into anotherwith the wave reconfiguring itself rapidlybut nonetheless smoothly. Classical orderhad been restored!Born, reviewing Heisenberg's math, realizedthat a mathematical system already existedwithin which quantum mechanics worked:it was known by a small group ofmathematicians and was called matrixalgebra. Soon it would be called matrixmechanics. Born supplied the mathematicsto Heisenberg's physics. Together withBorn's assistant, Pascual Jordan, they refinedand extended matrix mechanics.Unfortunately it was very complex stuff thatseemed to be largely a formal achievement,albeit one that well explained many of thepuzzling propositions inherent in quantum



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theory. Pauli, initially skeptical, and as washis wont, scathing in his criticism of matrixmechanics, nevertheless was able to us it toderive the Balmer series of spectral lines forhydrogen. It was a tour de force ofmathematics, one which, however, fewcould follow. To add to the mix, PaulDirac, a young physicist at Cambridge, in1925, presented a paper wherein heexplained his own rigorous mathematizationof quantum mechanics similar to that ofBorn, Jordan, and Heisenberg. Now,quantum mechanics could be explained bytwo systems with different foundations!Schroedinger, like so many others, found itquite arcane and difficult. When his waveequation appeared in early 1926, it wasgratefully received, consisting as it did ofold-fashioned differential equations. In hisNobel Prize lecture from 1933, he spoke ofhis desire through the wave equation to save"the soul of the old system" of mechanics.

Heisenberg, however, objected. At a lecturegiven by Schrodinger, he asked how wavemechanics could explain the photoelectriceffect or Compton scattering, both of whichprovided direct experimental evidence forthe proposition that light came in discrete,identifiable packets? Then, in the spring of1926 Schrodinger found that wavemechanics and matrix mechanics were notfundamentally different after all: they were,in effect, the same theory presented indifferent mathematics. The problem was inunderstanding how two such different viewsof nature could arise from the same source.Einstein and Heisenberg continued toobject. Max Born used wave mechanics to

describe how the collision of two particlesresulted in waves corresponding to therebound particles spread ou t something likeripples on a pond, "... smeared ou t in alldirections." Bu t a particle had to besomewhere; it couldn't disperse uniformlythroughout space. The end result of acollision had to amount to two distinctparticles moving off in well-defineddirections, what happened in the Comptoneffect. Born resolved the problem byproposing that the spreading waves leavingthe col1ision site described not actualparticles but their probabilities: where thewave was strong in a certain direction thisis where the rebounding particles were lesslikely to be seen. Schroedinger's equation,thus, generated not a classical wave, butrather the chance of finding an electronhere, there, or somewhere else in an atom.This harmonized with Heisenberg's matrixmechanics, wherein the physical presenceof an electron was a function of variousthings it might be doing, rather than somespecific indication of where it was. WhatBorn showed, according to Lindley, wasthat ". . . the recognition of wave mechanicsas dealing with probability didn't just clarifywhat Schrodinger's equation meant. It alsofleshed ou t the physical as opposed to thepurely mathematical connection betweenwave mechanics and matrix mechanics.Probability had slipped into physics in anew form.Born wrote in ]926 that it was no longerpossible to say what the specific outcome ofa collision would be. You could onlyspecify the probabilities of a range ofoutcomes. "Here the whole problem of



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determinism arises, . . . In quantummechanics there exists no quantity which inan individual case determines the result ofa collision ... I myself am inclined to giveup determinism in the atomic world." Butnot Einstein, who repeatedly and famouslysaid "I for one am convinced that He(God)does not throw dice." As Lindley wrote, "Ifprobability were to replace causality, then asfar as Einstein was concerned the rationalbasis for constructing theories of physicshad been swept away."Bohr and Heisenberg in Copenhagenbutted heads daily, the former arguing fora totally new physics, the latter trying tosave classical continuity. Dirac, also inCopenhagen at that time, ] 927, wasworking on the mathematics of translatingquantum problems into classical form. But,he found, try as he might, he could notdescribe both the position of a particle andits momentum simultaneously: it was as ifthe posi ti on -based accou n t and themomentum-based account were somehowdepicting two different quantum systems,not the same one in different ways. Paulifound the same thing, as did Heisenberg.There was no way to force a quantumsystem to yield up a description that wouldmake unambiguous sense in classical terms.In an attempt to resolve the matter practically by measuring pOSitIOn andmomentum, Heisenberg came up with whatbecame a famous example involving thecollison between an electron and a photon.He concluded that the more an observertried to extract information about theelectron's position, the less it was possibleto know about its momentum and vice

versa. There would always be an "inexactness." To Bohr, however, the inexactnesswas a manifestation of the contradictoryroles that particles and waves play inquantum events. As usual the two arguedincessan dy, bu t fi nally resolved the i rdisagreement and went to press using theword that Bohr preferred, "uncertainty",instead of "inexactness."Bohr, meanwhile, had developed his newphilosophy of "complementarity" accordingto which both the wave aspect and theparticle aspect of quantum objects hadnecessary but contradictory roles to play.Einstein, with his students Podolsky andRosen (EPR), found a way to invalidate thequantum uncertainty concept, that physicalproperties are fundamentally indefinite untilmeasured. Particles, they insisted, havedefinite properties: quantum mechanics isonly a partial theory, an incompleteportrayal of the underlying physical truth.Bohr responded in his usual careful,ponderous, opaque way showing how theEPR argument begins with a certain definition of physical reality, and then shows thatquantum mechanics doesn't stack up. Thekey is in the definition of physical reality,which Bohr indicates is inadequate tounderstand the phenomenon with whichquantum mechanics is concerned. Theobserver's choice of what to measure, not yetacted on, will affect how the partides revealthemselves later. In 1964, the physicist,John Bell, proposed certain experiments onsuitably arranged pairs of partides designedto test the EPR argument. Two decades laterthe experiment was carried out and it provedquantum mechanics to be wholly correct.



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Heisenberg left Copenhagen to teach inLeipzig, leaving Bohr to bring theuncertainty principle onto the internationalscientific stage. Bohr's correspondenceprinciple was the vehicle whereby thequantum world would transform seamlesslyinto our classical world. No matter whatsystem is under investigation, measurementwill disturb what is being measured and inmeasuring one aspect of a system the doorswill be closed on what else you might findout. This was the "Copenhagen Interpretation" of quantum mechanics.

Einstein tried mightily to argue againstquantum mechanics, bu t in vain. Whereashe lectured on the need for a synthesis ofconflicting views and thus, hopefully makethe underlying conflicts go away, Bohr'scomplimentarity reveled in contradiction.Einstein could not tolerate this, continuingto insist that beneath the apparent discontinuities and spontaneities determinismrules. His attempts to undermine quantummechanics by "thought experiments" invariably failed.The Nobel Prize in physics was awarded toHeisenberg in 1932, to Schrodinger andDirac in 1933, and to Born in ] 954. Thiswas, however, no t the end of the controversy pitting Einstein and Schrodingeragainst Bohr and Heisenberg. The latterwere challenged often by the former, themost famous exam pie being that ofSchrodinger's half-dead, half-alive quantumcat, whom Bohr dismissed as, "just silly."Bohr became the principle spokesman ofquantum mechanics and indeterminancy,speaking on psychology, philosophy and

applying his complimentarity principle tothe nature of life. In the ] 950s thephysicist, David Bohm provided an alternative interpretation of quantum mechanics,which claimed to restore determinism bymeans of what were called "hiddenvariables." According to Lindley, Einsteinfound Bohm's work unimpressive and"cheap." As Lindley indicates, Bohr'scomplimentarity principle developed littletraction in physics, but the uncertaintyprinciple became famous in many realmsoutside of physics, including literarydeconstruction and even the televisionseries, The West Wing.Heisenberg visited Einstein in Princeton in1954 a year before the latter's death.Einstein told Heisenberg, "I don't like yourkind of physics. There's consistency, but Idon't like it." Bohr and Heisenberg had acomplete break in friendship in ] 94].Heisenberg was allegedly involved inGermany's attempt to make use of nuclearpower and was shunned after the war bymany physicists. Heisenberg slowly workedhis way back into the scientific communitybecoming director of the Max PlanckInstitute in Munich where he died in 1976.The reader of Uncertainty will come awayfrom the book realizing to what extentuncertainty in the form of intuition plays apart, no t only in the objective quantumuniverse, but in the scientific process.Obviously in the present case it played ahuge roll, especially in Niels Bohr'screativity. It is almost as if the mathematization of Bohr's intuitively-derivedconcepts was but a device to confirm whatwas already known. And, with respect to

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the function of quantum processes, per se,it is my view, admittedly as one who is notexpert in physics or mathematics, but whohas spent his rather long professional lifestudying anomalous events and theory, thatquantum processes are not the rock-bottomfoundation of our physical world, bur existat the borderline of that place where the"intangible physical domain" meets the"tangible physical domain". I

CORRESPONDENCE: Richard A. Blasband, M.D. The Center for Funcrional Research, Sausalito, CA.

REFERENCES & NOTES1. R.G. Jahn & B.]. Dunne, A Modular Model of

Mind/Matter Manifestations (M5 ), Journal ofScientific Exploration 15, 3 (2001), pp. 299-329.

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