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hist-ph/0302041

ndtheDiscoveryofQuantumMechanics

KurtGottfried

1

CornellColloquium,January20,2003

Theo

whyamIgivingthistalk,youshouldask?Well,Itookmyfirstquantummechanicscourse

51yearsago,ingalwaysbeeninterestedin

thehistoryofphysics,IalsobrowsedthroughDirac’nceIhave

lyIwasdismayedthatnoattentionwasbeinggiven

tohiscentenary,ereforebothastonishedandpleased

toreceiveaninvitationfromNaturelastsummertowriteashortpieceontheoccasion.

2

Beingapedant,IthenspentalotoftimereadingDirac’spapersandbiographicalmaterials.

Natureisaimedatabroadscientificaudience,andononepageandwithoutequationsI

couldnotbegintogiveanunderstandabledepictionofDirac’ll

ivingthe

talktwice(inHelsinkiandCopenhagen)Iwasdisatisfied,sothisisamodifiedattempt.

s,withoutdoubt,oneofthe

greattheoreticalphysicistinthehistoryofoursubject;amongthefoundersof“modern”

physicshisstatureiscomparabletothatofBohrandHeisenberg,thoughnotEinstein.

Dirachadanastoundingphysicalintuitioncombinedwiththeabilitytoinventmathematics

atestpapersare,forlongstretches,

arguedwithinexorablelogic,butatcrucialpointsthereisanillogicaljumpintoentirely

heinventorsofquantummechanics,onlydeBroglie,Heisenberg,

Schr¨odingerandDiracwrotebreakthroughpapersthathavesuchillogicalandbrilliantly

ewhisbookbelongstothe

greatliteratureofthe20thCentury;speakquantum

mechanicsweusealanguagethatowesagreatdealtoDirac’swritings.

First,afewwordsaboutPaulDirac’ornonAugust8,1902,inBristol.

’sfatherwasadomestictyrant:

heforcedhischildrentospeaktohimonlyinFrench,forbademostsocialcontacts,and

’solder

brothercommittedsuicideandPaulwasexceptionallyintrovertedandreclusiveevenby

’sdifficultrelationshipwithhisfatherisevident

fromthefactthatheinvitedonlyhismothertoaccompanyhimtoStockholmwhenhewon

theNobelPrizein1933.

scholarshiptoCambridgebutcouldnotaffedoninhisparent’s

house,tookaseconddegreeinmathematicsatBristol,andthenwonabetterscholarship

whichallowedhimtomovetoCambridgein1923wherehebecamearesearchstudentof

2

,astostayatCambridgeuntilhisretirementin

acceptedaprofessorshipatFloridaStateUniversity,anddiedinFloridain

1984.

Tworecollectionsbyhiscolleagueswillgiveyousomeideaofhispersonality:

•IgorTamm:Heseemstotalkonlytochildren,andtheyhavetobeunderten.

•NevilleMott:Diracisratherlikeone’iteindifferenttocold,

discomfort,Heisquiteincapableofpretendingtothinkanythingthat

geofGalileohewouldhavebeenaverycontented

martyr.

WhenDiracwontheNobelPrize,heatfirstwantedtorefuseitbecausehewasafraidofthe

gedhismindafterRutherfordwarnedhimthatturningitdownwould

producefarmorepublicity.

AlthoughDiracfocusedonphysicsobsessively,helovedtotravelandtowalkinthe

mountains,elledaroundtheworldthree

times,fireboth

becomingquitefamousbythen,andthepresswantedaninterviewwhentheboatdocked

bergknowinghowshyhiscolleaguewas,toldthereportersDiracwas

unavailableeventhoughhewasstandingrightbesidehim.

’smostfamouswork,theDiracequationdiscoveredin1928

andthepredictionofanti-matterin1931,havelearned,

manyphysicistsareunawareofhowcrucialDirac’searliercontributionswere–thathe

playedakeyroleinthediscoveryanddevelopmentofnon-relativisticquantummechanics

helimitedtimeavailable,I

willconcentrateonDirac’,however,wanttogiveyouabird’seyeviewof

hiscareer,shownonthisslide.I’llcommentonmostoftheentrieslater.

•November1925–reformulationofHeisenberg’sgroundbreakingpaper:canonical

quantization,connectiontoPoissonbrackets–putshimsuddenlyatthecuttingedge

oftheoreticalphysics[overlapwithBorn,HeisenbergandJordan]

•August1926–identicalparticles,symmetricandantisymmetricwavefunctions(Fermi-

Diracstatistics)[overlapwithFermiandHeisenberg]

•December1926–transformationtheory–hisfavoritepaper[overlapwithJordan]

•February1927–quantumtheoryofradiation,emissionandabsorption

•April1927–scatteringoflight

•January1928–Diracequation

•December1929–proposesholetheory,protonashole

•1930–1steditionofPrinciplesofQuantumMechanics

•September1931–anti-matter,insamepaperasmagneticmonopole

•1932–appointedLucasianProfessorofMathematics(onceheldbyNewton)