Albert Abraham Michelson

Characterexperience

Michelson(AlbertAbrabanMichelsom,1852-1931),Polish-Americanphysicist,1852BorninStreno,Prussia(nowPoland)onDecember19,hemovedtotheUnitedStateswithhisparentsattheageof4.HegraduatedfromtheU.S.NavalAcademyin1873andtransferredtotheMaritimeCalendarBureauinWashingtonin1879.In1880,hewenttoEuropeforfurtherstudies,andhewastaughtbyfamousmasterssuchasHelmholtzinBerlin,Heidelberg,Parisandotherplaces.HereturnedtoChinain1882andwashiredasaprofessorofphysicsattheCaseSchoolofAppliedSciencesinCleveland.In1889,hewasaprofessorofphysicsatClarkUniversityinWorcester.In1892,heservedasthefirstdeanofthenewphysicsdepartmentattheUniversityofChicagountilhisretirementin1929.Inaddition,hewas:PresidentoftheAmericanAssociationfortheAdvancementofScience,DeanoftheAmericanAcademyofSciencesfrom1923to1927;alsoelectedasamemberoftheFrenchAcademyofSciencesandamemberoftheRoyalSocietyofLondon,anddiedinPasadenaonMay9,1931.

MichelsonwasborninStrzelno,asmalltowninPoland(thenitwasStrzelnoinPoznanProvinceinthePrussianEmpire),aJewishmerchant

son.Whenhewasonlytwoyearsold,hisfamilyimmigratedtotheUnitedStatesandfollowedhisfatherasabusinessman.HegrewuproughlythroughtheminingtownofMurphyinCaliforniaandVirginiaCityinNevada.

Michelsonismainlyengagedintheresearchofopticsandspectroscopy.Hehasdevotedhislifetotheprecisemeasurementofthespeedoflight.Duringhislifetime,hehasbeentheinternationalcenterofthemeasurementofthespeedoflight.Heinventedaninterferometer(Michelsoninterferometer)tomeasurethetinylength,refractiveindex,andwavelengthoflightwaves,whichplayedanimportantroleinthestudyofspectrallines.In1887,hecooperatedwiththeAmericanphysicistE.W.MoreytoconductthefamousMichelson-Morleyexperiment,whichwasoneofthemostsignificantnegativeexperiments,whichshakenthefoundationofclassicalphysics.Hedevelopedhigh-resolutionspectroscopyinstruments,improveddiffractiongratingsandrangefinders.Michelsonfirstadvocatedusingthewavelengthoflightasalengthreference,proposedthepossibilityofusinginterferenceeffectsinastronomy,andmeasuredthediameterofthestarBetelgeusewithastellarinterferometerofhisowndesign.

TheMichelsoninterferometerhecreatedisahugecontributiontoopticsandmodernphysics.Itcannotonlybeusedtodeterminethemicrolength,refractiveindex,andwavelengthoflightwaves,butalsoanimportantpartofmodernopticalinstrumentssuchasFourierSpectroscopy.In1926,thespeedoflightwasmeasuredmorepreciselywiththepolygonmirrormethod.

Becauseofthecreationofsophisticatedopticalinstrumentsandtheresearchonspectroscopyandbasicmetrologycompletedwiththeseinstruments,MichelsonwontheNobelPrizeinPhysicsin1907.

CharacterChronology

MichelsonwasbornonDecember19,1852inStreno,Prussia(nowPoland).

In1869,hewasselectedtostudyattheAnnapolisNavalAcademy.Aftergraduation,heservedasalecturerinphysicsandchemistryintheschool.

From1880to1882,hewasapprovedtostudyforpostgraduatestudiesinEurope,andsuccessivelystudiedattheUniversityofBerlin,theUniversityofHeidelberg,andtheFrenchInstitute.

In1883,hewasappointedprofessorofphysicsattheCaseSchoolofAppliedSciencesinCleveland,Ohio.

In1887,heandEdwardMoreyconductedthefamousMichelson-Moreyexperiment,whichruledouttheexistenceofether.Later,heturnedtotheuseofastronomicalopticalinterferometrytomeasurethediameterofstarsandthemeasurementofdoublestarbeamsplitters.

In1889,hebecameaprofessorofphysicsatClarkUniversityinWorcester,Massachusetts,whereheembarkedonagrandplanformetrology.

In1892,hebecameaprofessorofphysicsattheUniversityofChicago,andlaterservedasthefirstheadofthephysicsdepartmentoftheschool,wherehecultivatedhisinterestinastronomicalspectroscopy.

In1907,Michelson"inventedtheopticalinterferometeranduseditforspectroscopyandbasicmetrologicalinvestigations"(forhisopticalprecisioninstrumentsandthespectroscopicandmetrologicalinvestigationscarriedoutwiththeiraid)BecomethefirstwinneroftheNobelPrizeinPhysicsintheUnitedStates.Inthesameyear,hewontheCopleyMedal.

From1910to1911,heservedasthechairmanoftheAmericanAssociationfortheAdvancementofScience.

From1923to1927,heservedasthedeanoftheAmericanAcademyofSciences.

HediedinPasadena,CaliforniafromacerebralhemorrhageonMay9,1931,attheageof79.

Characterachievement

Etherdriftexperiment

Michelson’snameisassociatedwiththeMichelsoninterferometerandtheMichelson-Morleyexperiment,infactThisisalsothemostimportantcontributionofMichelson'slife.InMichelson'sera,peoplebelievedthatlightandallelectromagneticwavesmustbepropagatedthroughtheabsolutelystatic"ether",andwhetherthe"ether"existsandwhetherithasstaticcharacteristicswasstillamysteryatthetime.Someonetriedtomeasurethe"ethericwind"causedbythemovementoftheearthtothestationary"ether"toprovetheexistenceoftheetheranditsstaticcharacteristics,buttheyencountereddifficultiesduetothelimitationofinstrumentaccuracy.MaxwellwrotetoD.P.ToddoftheUnitedStatesMaritimeCalendarBureauin1879,suggestingthatRomer'sastronomicalmethodsshouldbeusedtostudythisproblem.Afterlearningaboutthissituation,Michelsondeterminedtodeviseamethodtoincreasethesensitivitytoonepartperbillionandmeasuretherelatedeffects.

In1881,heworkedintheHelmholtzlaboratoryoftheUniversityofBerlin,forwhichheinventedthehigh-precisionMichelsoninterferometerandperformedthefamousetherdriftexperiment.Hebelievedthatiftheearthrevolvesaroundthesunrelativetotheether,ittakesdifferenttimeforlighttopassthesamedistanceinthedirectionparalleltothedirectionoftheearth'smotionandperpendiculartothedirectionoftheearth'smotion.Therefore,whentheinstrumentrotates90°,theinterferenceproducedbythetwofrontsandbackswillbedifferent.Theremustbe0.04stripemovement.Michelsonusedtheoriginallybuiltinterferometerforexperiments.Theopticalpartofthisinstrumentwassealedontheplatformwithwax,whichwasveryinconvenienttoadjust.Itoftentookseveralhourstomeasureadata.Theexperimentyieldedanegativeresult.

Improvetheinstrument

In1884,withtheencouragementofRayleighandKelvinwhovisitedtheUnitedStates,hecooperatedwiththechemistMorley(Morley,EdwardWilliams,1838～1923)toimproveThesensitivityoftheinterferometerisstillnegative.In1887,theycontinuedtoimprovetheinstrument,andthelightpathwasincreasedto11meters.Ittook5daystocarefullyobservetherelativemotionoftheearthalongtheorbitandthestationaryether.Theresultisstillnegative.Thisexperimentarousedtheshockandattentionofscientists,andwascalledthe"twodarkcloudsinthehistoryofscience"alongwiththe"ultravioletdisaster"inthermalradiation.Later,morethan10peoplerepeatedtheexperiment,whichlastedfor50years.Furtherresearchonitledtonewdevelopmentsinphysics.AnotherimportantcontributionofMichelsonisthemeasurementofthespeedoflight.AsearlyaswhenhewasworkingattheNavalAcademy,hebecameinterestedinthemeasurementofthespeedoflightduetotheactualneedsofnavigation.

Measuringthespeedoflight

In1879,theworkofmeasuringthespeedoflightbegan.HeisthefourthtomeasurethespeedoflightonthegroundafterFizzo,Foucault,andCony.Hereceivedagrantfromhisfather-in-lawandgovernmentfunding,whichenabledhimtoimprovetheexperimentaldevice.HereplacedtherotatingmirrorinFoucault'sexperimentwitharegularoctagonalsteelprism,therebyextendingtheopticalpathby600meters.Thedisplacementofthereturninglightreaches133mm,whichimprovestheaccuracyandimprovesFoucault'smethod.Herepeatedlyandcontinuouslymeasuredthespeedoflight.Themostaccuratemeasurementwascarriedoutona22-milelightpathbetweenthemountainsofSouthernCaliforniafrom1924to1926,anditsvaluewas(299796±4)km/s.Michelsonwasneversatisfiedwiththeaccuracyhehadachieved.Healwayskeptimproving,experimentingrepeatedly,tirelessly,andstrivingforperfection.Ittookhalfacenturytodeterminethespeedoflight.Intheprocessofmeasuringthespeedoflightcarefullydesigned,heunfortunatelypassedawayduetoastroke.Hiscolleaguepublishedtheresultsofthismeasurement.Hereallydedicatedhislifetothemeasurementofthespeedoflight.Michelsonalsocontributedtobasicmetrics.

Determiningthereferencelength

In1893,heusedaninterferometerhedesignedtomeasurethewavelengthoftheredcadmiumline.Theexperimentshowedthatwhenthetemperaturewas15℃,thepressurewasgeneratedat760mmHg.Atpressure,thewavelengthoftheredcadmiumwireindryairis6438.4696angstroms,soheproposedtousethiswavelengthasthestandardlengthtoapprovethereferencemeterruler,andthereferencelengthsetbythismethodwillremainunchangedforalongtime.Therefore,itisrecognizedbytheworldandhasbeenuseduntil1960.

Interferometer

In1920,MichelsonandtheastronomerFGPeaseworkedtogethertoputa20-footinterferometerbehinda100-inchreflectingtelescopetoformastellarinterferometer.ItwasusedtomeasurethediameterofthestarBetelgeuse(thatis,thefirstvariablestarinOrion).Itsdiameterisquitelarge,withawirediameterof2.50×108miles,whichisabout300timesthediameterofthesun.Thismethodwaslaterusedtodeterminethediameterofotherstars.Michelson'sfirstimportantcontributionwastheinventionoftheMichelsoninterferometerandusedittocompletethefamousMichelson-Morleyexperiment.Accordingtoclassicalphysicstheory,lightandallelectromagneticwavesmustbepropagatedbythestaticether.Therevolutionoftheearthproducesmotionrelativetotheether.Therefore,intwoperpendiculardirectionsontheearth,thetimeforlighttopassthesamedistanceshouldbedifferent.Thisdifferenceshouldproduce0.04interferencefringemovementontheMichelsoninterferometer.In1881,Michelsondidnotobservethiskindofstreakmovementinexperiments.In1887,MichelsoncooperatedwiththefamouschemistMoreytoimprovetheexperimentaldevicetoachieveanaccuracyof2.5´10-10,butnomovementofthestripeswasfound.Theresultsofthisexperimentexposedtheflawsoftheethertheory,shakenthefoundationofclassicalphysics,andpavedthewayfortheestablishmentofthespecialtheoryofrelativity.Michelsonwasthefirstscientisttoadvocateusingthewavelengthoflightwavesasthelengthbenchmark.In1892,Michelsonusedaspecialinterferometertomeasurethewavelengthofthecadmiumredlineat6438.4696angstromsatatemperatureof15degreesCelsiusandapressureof760mmHgusingtheFrenchriceoriginaldeviceasthestandard.Therefore,1meterequals1553164timesthecadmiumredline.wavelength.Thisisthefirsttimethatmankindhasobtainedalengthbenchmarkthatwillneverchangeandcannotbedestroyed.Inspectroscopy,Michelsondiscoveredthefinestructureofthehydrogenspectrumandthehyperfinestructureofthemercuryandthalliumspectra.Thisdiscoveryplayedamajorroleinmodernatomictheory.Michelsonalsousedhisinvented"VisibilityCurveMethod"tostudyindetailtherelationshipbetweentheshapeofthespectrallineandthepressure,andtherelationshipbetweenthebroadeningofthespectrallineandthemovementofthemoleculeitself,andhisresultshavefocusedonmodernmolecularphysics,atomicspectroscopyandlaserspectroscopy.Emergingdisciplineshavehadasignificantimpact.

Echellegrating

In1898,heinventedanechellegratingtostudytheZeemaneffect.Itsresolutionismuchhigherthanordinarydiffractiongratings.Michelsonisanexcellentexperimentalphysicist.Theexperimentshecompletedareknownfortheiringeniousdesignandhighprecision.Einsteinoncepraisedhimasan"artistinscience."

Opticalinstrument

TheMichelsoninterferometerisaprecisionopticalinstrumentdesignedandmanufacturedbytheAmericanphysicistMichelsonandMoreyin1883tostudythedriftof"ether".Itusesthesub-amplitudemethodtogeneratedoublebeamstoachieveinterference.Byadjustingtheinterferometer,interferencefringesofequalthicknesscanbeproduced,andinterferencefringesofequalinclinationcanalsobeproduced.Itismainlyusedforthemeasurementoflengthandrefractiveindex.Ifoneinterferencefringeisobserved,themovingarmofM2isλ/2,whichisequivalenttotheairfilmthicknesschangebetweenM1andM2λ/2.Inmodernphysicsandmodernmetrology,thereareimportantapplicationsinexperimentssuchasthestudyofthefinestructureofspectrallinesandthecalibrationofstandardmeterswithlightwaves.Usingtheprincipleofthisinstrument,avarietyofspecialinterferometershavebeendeveloped.Interferencefringesarethetrajectoriesofequalopticalpathdifferencepoints.Therefore,toanalyzethepatternproducedbyacertaininterference,itisnecessarytofindthefunctionoftheopticalpathdifferencepositiondistributionofcoherentlight.Iftheinterferencefringesmove,theopticalpathdifferencecorrespondingtothefieldpointmusthavechanged.ThereasonforthechangeoftheopticalpathdifferencemaybethechangeofthelightlengthLorthechangeoftherefractiveindexnofacertainsectionofthemediumintheopticalpath.Orthethicknesseofthefilmhaschanged.