作者	L.D.Landau/等
出版社
出版时间	1999-05-01

特色：
In this edition the book has been considerably augmented and revised,with the assistance of L.P.Potaevskil throughout.New xections have been added on the magnetic properties of gases,the thermodynamics of a degenerate plasma,liquid crystals,the fluctuation theory of phase transitions of the second kind,and critical phenomena.……此书为英文版。

片断：TheimportanceofstatisticalphysicsinmanyotherbranchesoftheoreticalphysicsisduetothefactthatinNaturewecontinuallyencountermacroscop-icbodieswhosebehaviourcannotbefullydescribedbythemethodsofmechanicsalone,forthereasonsmentionedabove,andwhichobeystatisticallaws.Inproceedingtoformulatethefundamentalproblemofclassicalstatistics,wemustfirstofalldefinetheconceptofphasespace,whichwillbeconstantlyusedhereafter.Letagivenmacroscopicmechanicalsystemhavesdegreesoffreedom:thatis,letthepositionofpointsofthesysteminspacebedescribedbysco-ordinates,whichwedenotebyq,thesuffixitakingthevalues1,2,...,s.Thenthestateofthesystematagiveninstantwillbedefinedbythevaluesatthatinstantofthescoordinatesq,andthescorrespondingvelocitiesq,.Instatisticsitiscustomarytodescribeasystembyitscoordinatesandmomentap,,notvelocities,sincetbisaffordsanumberofveryimportantadvantages.Thevariousstatesofthesystemcanberepresentedmathematicallybypointsinphasespace(whichis,ofcourse,apurelymathematicalconcept);theco-ordinatesinphasespacearethecoordinatesandmomentaofthesystemcon-sidered.Everysystemhasitsownphasespace,withanumberofdimensionsequa)totwicethenumberofdegreesoffreedom.Anypointinphasespace,correspondingtoparticularvaluesofthecoordinatesq,andmomentapofthesystem,representsaparticularstateofthesystem.Thestateofthesystemchangeswithtime,andconsequentlythepointinphasespacerepresentingthisstate(whichweshallcallsimplythephasepointofthesystem)movesalongacurvecalledthephasetrajectory.Letusnowconsideramacroscopicbodyorsystemofbodies,aodassumethatthesystemisclosed,i.e.doesnotinteractwithanyotherbodies.Apartofthesystem,whichisverysmallcomparedwiththewholesystembutstillmacroscopic,maybeimaginedtobeseparatedfromtherest;clearly,whenthenumberofparticlesinthewholesystemissufficientlylarge,tbenumberinasmallpartofitmaystillbeverylarge.Suchrelativelysmallbutstillmacroscopicpartswillbecalledsubsystems.Asubsystemisagainamechani-calsystem,butnotaclosedone;onthecontrary,itinteractsinvariouswayswiththeotherpartsofthesystem.Becauseoftheverylargenumberofdegreesoffreedomoftheotherparts,theseinteractionswillbeverycomplexandintricate.Thusthestateofthesubsystemconsideredwillvarywithtimeinaverycomplexandintricatemanner.Anexactsolutionforthebehaviourofthesubsystemcanbeobtainedonlybysolvingthemechanicalproblemfortheentireclosedsystem,i.e.bysettingupandsolvingallthedifferentialequationsofmotionwithgiveninitialcon-ditions,which,asalreadymentioned,isanimpracticabletask.Fortunately,itisjustthisverycomplicatedmannerofvariationofthestateofsubsystemswhich,thoughrenderingthemethodsofmechanicsinapplicable,allowsadifferentapproachtothesolutionoftheproblem.Afundamentalfeatureofthisapproachisthefactthat,becauseoftheextremecomplexityoftheexternalinteractionswiththeotherpartsofthesystem,duringasufficientlylongtimethesubsystemconsideredwillbemanytimesineverypossiblestate.Thismaybemorepreciselyformulatedasfollows.LetApAqdenotesomesmall"volume"ofthephasespaceofthesubsystem,correspondingtocoordinatesq,andmomentaplyinginshortintervalsAq,andApWecansaythat,inasufficientlylongtimeT,theextremelyintricatephasetrajectorypassesmanytimesthrougheachsuchvolumeofphasespace.LetbethepartofthetotaltimeTdurinewhichthesubsystemwasinthegivenvolumeofphasespaceApAq?WhenthetotaltimeTincreasesindefinitely,theratiot/Ttendstosomelimit(1.1)Thisquantitymayclearlyberegardedastheprobabilitythat,ifthesubsys-temisobservedatanarbitraryinstant,itwillbefoundinthegivenvolumeofphasespaceApAq.Ontakingthelimitofaninfinitesimalphasevolumedqdp=dq1dq2...dq,dp1dp2...dp,(1.2)wecandefinetheprobabilitydwofstatesrepresentedbypointsinthisvol-umeelement,i.e.theprobabilitythatthecoordinatesqandmomentap,havevaluesingiveninfinitesimalintervalsbetweenq,,p,andq dq,,p dprThisprobabilitydwmaybewrittenwhere(,...,p,,q,...,q,)isafunctionofallthecoordinatesandmomenta;weshallusuallywriteforbrevity(p,q)orevensimply.Thefunctiong,whichrepresentsthe"density"oftheprobabilitydistributioninphasespace,iscalledthestatisticaldistributionfunction,orsimplytheForbrevity,weshallusuallysay,asiscustomary,thatthesystem"isinthcvolumepqofphasespace",mearningthatthesystemisinstatesrepresentedbyphasepointsintbatvolume.Inwhatfollowsweshallalwaysusetheconventionalnotationdpanddqtodenotethcproductsofthedifferentialsofallthemomentaandallthecoordinatesofthesystemrespectively.