Newdiscoveriesintheworldofparticles
Therevolutioninphysicsattheendofthe19thcenturyandthebeginningofthe20thcenturybrokeinfromtheatomic"entity",andwithitthesecretsofthestructureofmatterwererevealedlayerbylayerOpen,toshowmankindarichandcolorfulnaturalsceneinthemicroscopicfield.Thedevelopmentofmicro-physicshashadahugeimpactontheentirenaturalsciences.Inthefirsthalfofthe20thcentury,alldisciplinesmarchedintotheirownsmall-scalefields,andcombineddeeperinvestigationswithlarger-scaleexplorations,andachievednewbreakthroughsinbothmacroandmicroresearch.
Thedevelopmentofmodernnaturalsciencesisrealizedthroughthemutualpromotionofmacroscopicresearchandmicroscopicresearch.Ahighdegreeofdifferentiationandahighdegreeofintegrationisanimportantcharacteristicofthedevelopmentofmodernscience.Thefollowingisanoverviewofseveralaspectsofthedevelopmentofmodernnaturalscience:
Atomicnucleus
Thenucleus(English:Atomicnucleus)isthecorepartoftheatom.Partialquality.Thenucleusiscomposedofprotonsandneutrons.Whensurroundedbyelectronsequaltotheamountofprotons,atomsareformed.Thenucleusisextremelysmall.
Alphaparticlescatteringexperiment
Intheexperiment,collimatedalpharaysareusedtobombardthegoldfoilwithathicknessofmicrometers,anditisfoundthatmostofthealphaparticlesareshiningstraightthroughthethingoldfoil,withlittledeflection.However,thereareafewalphaparticlesthathaveamuchlargerdeflectionanglethanpredictedbytheThomsonmodel.About1/8000alphaparticleshaveadeflectionanglegreaterthan90°,andevenscatteringwithadeflectionangleequalto150°isobserved.Thisiscalledlarge-anglescattering.ItcannotbeexplainedbyThomson'smodel.
Thomsonmodel
TheThomsonmodelbelievesthatthepositivechargeoftheatomisevenlydistributedintheentireatomicsphere(theorderofmagnitudeofthespherediameteris10-10squaremeters),withThenegativelychargedelectronsarescatteredinthepositivecharge.Theseelectronsaredistributedinsymmetricalpositions,asifraisinsareevenlydistributedinacake.Sopeoplecallitthe"raisincake"model.Whentheseelectronsareatrestinanequilibriumposition,theelectronswillvibrateandtheatomswillemitlight.
In1911,Rutherfordproposedanuclearmodeloftheatom(alsoknownasthenuclearstructuremodeloftheatom).Themassassociatedwiththepositivechargeisconcentratedinthecentertoformthenucleus,andtheelectronsmovearoundthenucleusoutsidethenucleus.Fromthis,theαparticlescatteringformulaisderived,whichexplainsthelargeanglescatteringofαparticles.Rutherford’sscatteringformulawaslatersystematicallyverifiedbyGeigerandMarsden’simprovedexperiments.Accordingtothedataoflarge-anglescattering,itcanbeconcludedthattheupperlimitoftheradiusoftheatomicnucleusis10-14meters[1].Thisexperimentcreatedaprecedentinthestudyofatomicstructure.ThisexperimentoverturnstheraisinbunmodelofatomsproposedbyJJThomsonin1903.Itisbelievedthatthepositivechargeandmassoftheatomarelinkedtogetheranduniformlyandcontinuouslydistributedintherangeoftheatom.Theelectronsareembeddedinitandcanmakesmallvibrationsattheirequilibriumpositions.Itlaidthefoundationfortheestablishmentofmodernnucleartheory.
Experimentalresultsshowthatthevastmajorityofalphaparticlesstillmoveintheoriginaldirectionafterpassingthroughthegoldfoil,butafewalphaparticleshaveundergonealargedeflection,andaverysmallnumberofalphaparticleshavedeflectedmorethan90°,Andsomeevenalmostreach180°andbebouncedback.Thisisthescatteringphenomenonofalphaparticles.
3.Elementaryparticles
Electrons,protonsandneutronsthatmakeupthenucleus,andphotonsasradiationunitsarecalledelementaryparticles.Amongthem:
(1)Thediscoveryofprotons
In1919,whenRutherfordbombardednitrogenwithastrongraysource,hediscoveredthatanewkindofparticlewasproduced,whichhadapositivecharge.,Qualityratio.Theparticlesaresmallandhavealongrange.Thisisthefirsttimethatthenucleushasbeentransformedbyartificialmethods,namely:(14,7)N+(4,2)He→(17,8)O+(1,1)H,parenthesesindicatemassnumberandprotonnumber.Inthesameyear,Rutherfordbombardedhydrogenwithalphaparticles,provingthatthepositivelychargedparticle(1,1)Hproducedwasahydrogennucleusandnameditaproton.Itisconfirmedthatthereareprotonsinthenucleus,andprotonsarethebasicparticlesthatmakeupthenucleus.Theelectricalpropertiesofprotonsareoppositetothoseofelectrons,buttheamountofchargeisequal.Theatomsareelectricallyneutraltotheoutside.
(2)Thediscoveryofneutrons
In1932,Rutherford’sgraduatestudentandcollaborator,Chadwick(1891-1974)intheUnitedKingdomrepeatedtheirexperiment,Afterdetailedanalysisandresearch,itisprovedthattheberylliumraysaretheneutralparticlesorneutronspredictedbyRutherford.Thisreactionis:(9,4)Be+(4,2)He→(1,0)n+(12,6)C.
Thediscoveryofprotonsandneutronsuncoveredthemysteryofthemicroscopicfieldandprovidedanewweapon——ProtonandNeutronCannonballs
From1930to1932,heinventedthecyclotron,staticaccelerator,andhigh-pressuremultipliercapableofobtaininghigh-speedprotons.Therearealsotheestablishmentofaradium-berylliumneutronsourcecapableofemittingfastneutrons,andtheimprovementofvariousdetectionmethodssuchasspectrometers,whicharealsoimportantconditionsfornuclearphysicsresearch.From1934to1937,morethan200artificialradioisotopeswereproduced.Bytheendof1937,asmanyas600nuclearreactionshadbeenstudied.Between1934and1939,AmericanItalianphysicistFermi(1901-1954AD),GermanphysicistHahn(AD1879-1968)andothersusedneutronstobombardvariouselementsanddiscoveredavarietyofradioactiveisotopes.Theartificialnuclearfissionreactionwiththeuraniumnucleusbeingshattered,andwhentheuraniumsplits,itwillreleaseneutrons,formingachainreaction,andreleasinghugeenergy,thusstartingtheuseofatomicenergy.
Cosmicrays
(1)Whatarecosmicrays
Inthemarchofpeopleintothemicroscopicworld,inadditiontousingnaturalradiationandfastparticlesproducedbyaccelerators,theyalsoDiscoveranatural"laboratory",thatis,cosmicrays.
Cosmicrays,alsoknownascosmicrays,arechargedhigh-energysubatomicparticlesfromouterspace.Theymayproducesecondaryparticlesthatpenetratetheearth’satmosphereandsurface.About89%ofcosmicraysaresimpleprotonsorhydrogennuclei,10%areheliumnucleioralphaparticles,and1%areheavyelements.Thesenucleiconstitute99%ofthecosmicrays.Lonelyelectrons(likebetaparticles,althoughthesourceisstillunclear),makeupthevastmajorityoftheremaining1%;gammaraysandultra-highenergyneutrinosaccountforonlyaverysmallpart.
(2)Thediscoveryprocessofcosmicrays
In1912,GermanscientistViktorHanstookanionizationchamberinanexperimenttomeasurethedegreeofionizationofairwhenhetookoffbyaballoon.Itwasfoundthatthecurrentintheionizationchamberincreasedwiththeelevation,anditwasdeterminedthatthecurrentwasgeneratedbyaverypenetratingrayoutsidetheearth,sosomepeoplenamedit"cosmicrays."
Discoveryofcosmicrays
(1)Positron
(2)Interconversionbetweenpositiveandnegativeelectronpairsandphotons
(3)Thediscoveryofmesons
1)πmesonsinvolvedinnuclearforce
2)Muonsthathardlyinteractwithnuclei(onlyparticipateinweakinteractions)
Thediscoveryofthefirstgenerationofparticles
By1947,peoplehadrealizedthat14kindsofelementaryparticles,ifarrangedinorderofincreasingmass,wouldbephotons,leptons(includingpositiveandnegativeelectrons,positiveNegativemuonsandprophetictrinosandantineutrinos),threekindsofpions,baryons(includingneutrons,protons,andpropheticantineutronsandantiprotons).
Thediscoveryofthesecondgenerationofparticles
In1947,therewassomethingtheoreticallyunexplainableinthestudyofelementaryparticles.Thisisthediscoveryofanelectronwithamassofapproximately1000inthecosmicrays.TheKmesonisabout2200timestheelectronmassandthehyperonisabout2200timestheelectronmass.Theseparticleshavestrangeproperties,thatis,theyallproducefastanddecayslowly,sotheyarecalledstrangeparticles.Makethebasicparticlesknowntoreach30kinds.Thesestrangeparticlesarecalledthesecond-generationelementaryparticles.
Thediscoveryofthethirdgenerationofparticles
Sincethe1960s,physicistshavediscoveredalargenumberofresonantparticleswithextremelyshortlifetimes,makingthetotalnumberofelementaryparticlesTherearemorethan400kinds.Resonantparticlesarealsocalledthird-generationelementaryparticles.
Thelargenumberofdiscoveriesofelementaryparticlesandtheirsystematicclassificationhavemadepeoplerealizethatelementaryparticlesarenotthefinalentityofthematerialstructure,butalsohaveinternalstructures.
1956year,JapanesephysicistMasaichiSakata(1911-1970AD)proceededfromtheideathatmatterisinfinitelyseparable,andbelievedthatallparticipantsarestronglymutuallyTheactingparticles(hadron)areallmadeupofthethreebasicparticlesofprotons,neutrons,andhyperonsConstituted.TheSakatamodelexplainssomefacts,butitalsoclearlycontradictssomeexperiments.
1964Intheyear,theAmericanphysicistGellman(1929AD—)establishedtheperiodictableofhadronsandproposedThequarkmodel,believesthatthreekindsofquarks(andtheirantiquarks)withfractionalchargesconstituteelementaryparticles.
1965From1966to1966From,Chinesephysicistsputforwardnewinsightsinthestudyofelementaryparticles.TheyItisbelievedthatthegenerationanddestructionofsymmetrycanonlybeareflectionofacertainstructureinsidethehadrons,andbasedontheanalysisofthepreviousresearchresults,thestratonmodelisproposed.Physicistsfromvariouscountriesareconductingin-depthresearchonthequarkmodelandthestratonmodel,butsofarhavenotfoundtheexistenceof"freequark",norhasfoundevidencethatquarksorstratonscanexistalone.Somepeoplebelievethatquarksorstratonswillalwaysbeconfinedinhadrons.
Theexplorationoftheinteractionforcebetweenparticles
Thenewdiscoveryofparticlespromptedpeopletostartthediscussionofthewayofinteractionbetweenparticles.Therearefourbasicformsofinteractionbetweenparticles,namelyfourbasicforces.Themaincharacteristicsofthefourbasicforcesareshowninthefollowingtable:
Themaincharacteristicsofthefourbasicforces
Asearlyasthe1940s,somepeoplewerediscussingtheweakinteractionandelectromagneticinteraction.Unite.In1961,GlasowintheUnitedStatespublishedthefirstpaperwithactualprogress,whichlaidthefoundationfortheweak-potential-theory.In1967,WeinbergoftheUnitedStates(1933AD)andSalamofPakistan(1926AD)respectivelyproposedtheUnifiedModelTheoryofWeakElectricInteraction.Thistheoryhasbeensupportedbyaseriesofexperiments.Inspiredbythistheory,peoplearediscussingthethreeinteractivetheoriesofstrong,weak,andelectric,namelythegrandunifiedtheory,andthisexplorationisstillgoingon.
ElementaryParticles
Hadrons
Hadronsarethegeneraltermforallparticlesthatparticipateinpowerfulinteractions.Theyarecomposedofquarks.Therearesixtypesofquarksthathavebeendiscovered.Theyare:topquark,upperquark,lowerquark,strangequark,charmquarkandbottomquark.Amongthem,thetheorypredictstheexistenceoftopquark,whichwasdiscoveredinFermilab,USAonJanuary30,2007.Mostoftheexistingparticlesarehadrons,andprotons,neutrons,andpionsareallhadrons.(Inaddition,anti-matter,thefamousanti-quark,hasbeendiscoveredandthemethodofitsuseisbeingstudied.Fromthiswespeculatethattheremayevenbeanti-earthandanti-universe.)Thestrangethingisthatsomeofthequarksareheavierthanprotons.Oneissueremainstobestudied.
Leptons
Leptonsarethegeneraltermforparticlesthatonlyparticipateinweakforce,electromagneticforce,andgravitation,butdonotparticipateinstronginteraction.Therearesixtypesofleptons,includingelectrons,electronneutrinos,muons,muonneutrinos,tauandtauneutrinos.Electrons,muonsandtauarecharged,allneutrinosareuncharged,andallneutrinoshaveantiparticles;tausareimportantparticlesdiscoveredin1975anddonotparticipateinstronginteractions.Theybelongtoleptons.Butitsmassisveryheavy,3600timesthatofelectronsand1.8timesthatofprotons,soitisalsocalledpalepton.
Propagator
Propagatoralsobelongstoelementaryparticles.Thereare8kindsofgluonsthattransmitstrongeffects.Theywerediscoveredindirectlyinthethree-jetphenomenonin1979.Theycanformgluonspheres.Duetothephenomenonofcolorconfinement,theycannotbedirectlyobservedsofar.Photonstransmitelectromagneticinteractions,whileweakW+,W-andZ0aretransmitted,andgluonstransmitstronginteractions.Theheavyvectorbosonwasdiscoveredin1983.Itisveryheavy,80to90timesthatofaproton.
Fermions
Basicfermionsaredividedintotwocategories:quarksandleptonquarks
Experimentshaveshownthatthereare6kindsofquarks(quarks),andtheirrespectiveOfantiparticles.These6kindsofquarkscanbedividedinto3"generations".Theyare
Firstgeneration:u(upperquark)d(lowerquark)
Secondgeneration:s(strangequark)c(charmquark)
Thirdgeneration:b(bottomquark)t(topquark)
Itisalsoworthpointingoutthatthereasonwhytheywerenotdiscoveredbyearlyscientistsisthatquarksneverexistalone(topquark)Exception,butthetopquarkistooheavyanddecaystoofasttobemadebyearlyexperiments).Theyalwaysformapairofmesons,orthreetogetherformbaryonssuchasprotonsandneutrons.Thisphenomenoniscalledquarkconfinementtheory.Thisiswhyearlyscientistsmistakenlybelievedthatmesonsandbaryonswereelementaryparticles.
Boson
Boson(English:boson)isaparticlewhosespinisanintegeraccordingtoBose-Einsteinstatistics.Gaugebosonisakindofparticlesthatmediateandtransferinteractionsbetweenparticles.Thereasontheyarecalled"gaugebosons"isbecausetheyarecloselyrelatedtotheYang-Millsgaugefieldtheoryofelementaryparticles.
Therearefourkindsofinteractionsinnature,sogaugebosonscanalsobedividedintofourcategories.
Gravitationalinteraction:graviton
Electromagneticinteraction:photon
Weakinteraction(interactionthatdecaysatoms):Thereare3typesofWandZbosons.
Stronginteraction(interactionbetweenquarks):gluon
62kindsofelementaryparticles
1.Lepton(12kinds)Leptonsmainlyparticipateinweakeffects,andchargedleptonsalsoparticipateinelectromagneticeffects,butdonotparticipateinstrongeffects.01,electron02,positron(antiparticleofelectron)03,muon04,anti-muon05,tau06,anti-tau07,electronneutrino08,anti-electronneutrino09,Muonneutrino10,anti-muonneutrino11,tauneutrino12,anti-tauneutrino2,quark(36types)Quark,layer,deficient(6flavors×3colors×positiveAntiparticle=36types)13,redupquark14,anti-redupquark15,greenupquark16,anti-greenupquark17,blueupquark18,anti-blueupquark19,reddownquark20,anti-reddownquark21.Greenlowerquark22,anti-greenlowerquark23,bluelowerquark24,anti-bluelowerquark25,redcharmquark26,anti-redcharmquark27,greencharmquark28,anti-greencharmquark29,bluecharmquark30,Anti-bluecharmquark31,redstrangequark32,anti-redstrangequark33,greenstrangequark34,anti-greenstrangequark35,bluestrangequark36,anti-bluestrangequark37,redtopquark38,anti-redtopquark39,Greentopquark40,anti-greentopquark41,bluetopquark42,anti-bluetopquark43,redbottomquark44,anti-redbottomquark45,greenbottomquark46,anti-greenbottomquark47,bluebottomquark48,Anti-blue-bottomquark3.Gaugeboson(gaugepropagator)(14types)49,gravitational-neutralgluon(typeⅠopenstring)upquark-upquark50,gravitational-neutralgluon(Ⅰ)Typeopenstring)anti-upquark-anti-upquark51,magnetictype-neutralgluon(typeⅠclosedstring)(anti)downquark-(anti)downquark52,magnetictype-neutralgluon(typeⅠclosed)String)quark-antiquark53,cationicgluonup-quark-downquark54,cationicgluonup-quark-downquark55,positive-electricgluonanti-upquark-anti-downquark56,cationicgluonAnti-up-quark-anti-downquark57,photon(lightquantum)58,gravitons(stillahypothesis)59,W+boson60,W-boson61,Zboson62,HiggsbosonHiggsBoson
FromCondensedMatterPhysicstoAstrophysics
CompletePhysicsSystem
Quark-ElementaryParticle-AtomicNucleusandAtom-Molecule-Condensedmatter(solidandfluid)-Earthandothercelestialbodies-galaxiesandtheentireuniverse
Newadvancesincondensedmatterphysics
Firstofall,itisrelatedtoultrahighpressure,highvacuum,andultrahightemperatureItisrelatedtotheacquisitionofspecialconditionssuchasextremelylowtemperatureandstrongmagneticfield.
In1905,BridgmanoftheUnitedStates(1882-1961)inventedanultra-highpressuredevicewithapressureof10,000atmospheres.Healsousedthisdevicetoconductexperimentalresearchonthephysicalpropertiesofrocksunderhighpressure.High-pressurephysicshasbecomethetheoreticalbasisofhigh-pressureengineering(suchasman-madediamond).
Syntheticdiamonds(2photos)
Theapplicationofelectriclightinginthe19thcentury,especiallytheinventionofelectrontubes,promotedthedevelopmentofvacuumtechnology.
From1910to1915,Germany’sAl-Qaeda(1878-1945)inventedoil-sealedrotatingmolecularpumpsandmercurydiffusionvacuumpumps,whichcouldcreate10+-10-'torr(1Torr).Thevacuumisequalto133.3224Pa),andtheacquisitionofhighvacuumisanindispensableconditionforstudyingthepropertiesofsolidsurfaces,lasers,andmaterialprocessing.
Thestudyofphysicalpropertiesatextremelylowtemperaturesisanimportantbranchofsolidstatephysics.Ithasbeenknownforalongtimethattheendothermicreactionduringgasliquefactionwillleadtotheappearanceoflowtemperature.In1881,VanderWaalsintheNetherlands(1837-1923AD)carriedoutthestudyoftherelationshipbetweengasandliquidatlowtemperatures.
From1906to1913,theGermanNernst(1864-1941AD)lowtemperatureresearchputforwardthethirdlawofthermodynamics,whichprovedthatabsolutezeroisimpossibletoachieve.
TheDutchphysicistUnnes(1853-1926AD)discoveredthattheresistanceofmetalssuchasmercury,lead,tin,etc.suddenlydroppedtoasuperconductivitybelowthenormalvalueof10-9atultra-lowtemperature.
In1937,theformerSovietscientistPilchar(1894-AD)discoveredthesuperfluidityofliquidheliumatextremelylowtemperatures(thatis,theviscosityoftheliquidisextremelysmall).Onthisbasis,physicistsproposedatwo-fluidmodelofsuperconductivityandliquidhelium,andLandau,whoworkedwithKapil(1908-1968AD,establishedthequantummechanicstheoryofsuperfluidity.
ThefamousAmericanphysicistBaden(AD1908-),Cooper(AD1930-)andSchriever(AD1931-)collaboratedtoproposeasuperconductingmicroscopicmodel.
BadenandXiaoKlee(1910-AD)andBratan(1902-AD)collaboratedandmadeimportantachievementsintheresearchofsemiconductormaterialsandinventedthetransistor.
Otheraspectsofsolid-statephysics(crystalstructure,metalPhysics,solidmagnetism,dielectricphysics,solidluminescence,etc.)havealldevelopedinthe20thcentury,especiallyinthepast30years.
Astrophysics
Fromtheperspectiveofnon-lifephenomena,whereAllobjectswithaspatialscalegreaterthan10ˉ6~10ˉ4cmaremacroscopicobjects,whichincludenotonlydustintheairandobjectsontheground,butalsomountains,lakesandseas,geologicalstructuresystems,andevenplanets,stars,andplanetarysystems(suchasthesolarsystem)./p>
SolarSystem(2photos)
Inaslightlylargerscale,thegeologyofthe19thcenturyhasconductedpreliminarystudiesontheclassification,structureandoriginofstrata,butthatTheobjectoftimeismainlylimitedtothelocalareaoftheearth'ssurface.Astronomyinthe19thcenturyandearlieralsomainlystudiedthetrajectory,size,andmassofthesolarsystemandafewstars,andtheluminosity,temperature,andmagnetismofmorecelestialbodiesandinterstellarmatter.,Density,structure,chemicalcomposition,energysource,etc.arestilllackinginunderstanding.Geophysicsandastrophysicsarestillintheprocessofformation.
Thehistoryofchangesinthehumanviewoftheearth
1)19thcenturyItisgenerallyacceptedthattheearthisformedbythegradualshrinkageofhotobjects.Afterthediscoveryofradiationinthecrustalrocks,theviewthattheearthhasinternalthermaldynamicshasgraduallyformed.However,althoughscientistsinthe19thcenturyrecognizedthattheearthhasitsevolutionaryhistory,theybelievedthatthelandandoceanontheearthbasicallydidnotchangemuchaftertheywereformed.Thelandisfixedandtheoceanispermanent.
2)Continentaldrifttheory
Inthe20thcentury,somenewdiscoveriesingeologybrokethisviewoftheearth.In1921,GermanscientistWegener(1880-1930AD)proposedtheideaofcontinentaldriftbasedonthesimilarityofcoastlinesonbothsidesoftheAtlanticOcean,thekinshipbetweenorganismsandpaleontology,andthecontinuityofgeologicalandgeographicphenomena.HebelievesthatinthePaleozoiceraingeologicalhistory,therewasonlyonehugelandintheworld-theUnitedAncientLand,surroundedbyanocean.SincetheMesozoic,theUnited
Theancientlandbegantosplitanddrift,andgraduallyformedintoseveralcontinentsandislands.Theoceanswereseparatedtoformseverallargeoceansandseveralsmallseas.
3)Thetheoryofmantleconvection
In1928,theBritishHolmes(1890-1965AD)proposedthetheoryofmantleconvection.Hebelievedthatthemantlematerialhasveryslowthermalconvection,whichleadstoThecontinentmoveshorizontallyinacertaindirection,andthelatestexplanationofthedriftmechanism
4)Submarineexpansiontheory
In1961,HessandDiezintheUnitedStatesestablishedthesubmarineexpansiontheorybasedonalargeamountofpaleomagneticdata.Theybelievethatthemantlematerialgushesoutfromthemid-oceanridgesandriftvalleysandcondensestoformanewseabed,pushingthepreviouslyformedseabedtoexpandtobothsidesatarateofabout1to5centimetersperyear,andtheoldstratumsinkswhenitreachesthedeeptrench.Inthemantlematerial,itisrenewedeverytwoorthreebillionyears.Thetheoryofsubmarineexpansionisadevelopmentofthetheoryofcontinentaldrift.
5)Thetheoryofplatetectonics
In1965,geologistsfromWilson,Hess,andCambridgeUniversitygatheredinCambridge,England,andfoundedonthebasisofaseriesofpreviousachievements.Basedonthetheoryofplatetectonics,itisbelievedthattheentirelithosphereoftheearthcanbedividedintosixmajorplatesandseveralsmallplates.Thebasicreasonforglobalgeologicalstructureisduetotheinteractionoftheseplates.Theplatetheoryclarifiedthebasicaspectsoftheformationanddevelopmentoftheearth,andmadethetheoryofcontinentaldriftappearinanewform.
Advancesinastrophysics
Astronomicalchemistryisthemostimportantresearchinastronomyinthe20thcenturyInthefield,thehypothesisthatstarsaregeneratedfromsuper-densematterorthindiffusematterandgraduallyevolveisproposed.Thestudyoftheuniverseandtheevolutionoftheuniversehasattractedmuchattentionfromastrophysics,andamodeloftheexpandinguniversehasbeenproposed.Attheendofthe1940s,theAmericanscientistKamov(1904-1968AD)linkedthestudyofelementaryparticleswiththetheoryofcosmicexpansionandproposedthetheoryoftheBigBanguniverse,whichbelievedthatthehumanuniverseoriginatedfromextremelyhigh-density"primitivefireballs."TheBigBang,andthenevolvedintotheworldtodayaftermorethantensofbillionsofyears.Inthe1960s,duetothediscoveryof30Kmicrowavebackgroundradiation,theBigBanghypothesiswasacceptedbymostastronomers.
(1)Evolutionoftheuniverse
1)Theveryearlystageoftheevolutionoftheuniverse,theformationofelementaryparticles.From0secondto10-36secondsintheevolutiontimeoftheuniverse,theuniverseexpandedrapidlyandquarkparticleswereproduced.Hadronsweregenerated10_6secondsago,andleptonsweregenerated10_2secondsago.Inthisstage,sincetheneutrondecaysintoaproton,electronsandneutrinosarereleased,andtheelectronandpositronmeetandannihilateintotwophotons,sophotonradiationdominates.
2)Radiationstageandnuclearsynthesisstage.From1secondto104years.Inthebeginning,theuniversewasdominatedbyradiation,andphysicalobjectsonlyoccupiedasecondaryposition.At3minutes,thetemperaturedroppedto109K,andnuclearreactionsbegan.Neutronsandprotonssynthesizedeuterons,andthensynthesizeheliumnuclei,andtherealobjectgraduallydominates.
3)Thephysicalstage.After104years,thetemperaturedroppedto10'K,andstableatomswereformed.Radiationintheuniversetookabackseat,andphysicalobjectsoccupiedamajorrole.Thegravitationalforcebetweenphysicalobjectsbegantoplayamajorrole.Afterthat,thesparsegaseousobjectsintheuniversebegantoformprimitivenebulae,andthenformedgalaxyclusters,andthendifferentiatedgalaxies(suchastheMilkyWay)fromgalaxyclusters.
4)Thefuturestage.Onemodelbelievesthattheexpansionoftheuniversewillgraduallyslowdownundertheactionofuniversalgravitation.Afterreachingacertainmaximumvolume,itwillbegintoshrink,untilitshrinkstothe"primitivefireball"state,andthenexplodesandexpands.
(2)Theevolutionofstars
1)Thegravitationalcontractionphase,whichisthejuvenilephaseofastar.Themainroleistheself-attractionofdiffusematterduetogravitation.Thediffusematerialshrinksquicklytoformastellarembryo,andthetemperaturerises,andthengraduallyshrinksintoastarwithasurfacetemperatureofseveralhundreddegreesCelsiusandcapableofemittinginfraredrays.
2)Mainsequencestarstage,whichisthestar'sadultstage.Thecontractioncausesthetemperatureinthecenterofthestartorisetonearlyonemilliondegrees,andthereactionofhydrogennucleifusionintoheliumnucleibegins,releasinghugeenergy,andthetemperaturecontinuestorise.Repulsionandattractionareevenlymatched.Thestarneithershrinksnorexpands,andbecomesarelativelystablehost.Sequencestarsandemitbrilliantstarlight.Thestarstaysinthisstageforthelongesttime.Forexample,thesunisinthemainsequencestarstage.4.6billionyearshavepassed,anditwilltake5billionyearstoenterthenextstage.
3)Theredgiantphase,whichisthemiddle-agedageofthestar.Theheliumnucleiformedbyhydrogennuclearfusionaccumulatesinthecenterofthestar.Theradiationpressureprovidedbythehydrogennuclearfusionreactionatitsedgecannotwithstandthegravitationalforce,andtheattractionexceedstherepulsion,causingthecentralareaofthestartoshrink.Partofthereleasedgravitationalpotentialenergyheatsthecentralareaandraisesitstemperatureto100milliondegrees.Thestar'sshellexpandssharply,thesurfaceareaexpands,andthesurfacetemperaturedecreasestoemitredlight,soitiscalledaredgiant.
4)Thepulsationandexplosionphase,whichistheoldageofthestar.Aftertheheliumfuelinthecenterofthestarisexhausted,thermonuclearreactionssuchascarbonfusion,oxygenfusion,andsiliconfusionwilloccursuccessively,andthevolumeandbrightnessofthestarwillchangeperiodically.Inthecyclicalpulsation,alargepartofthestarswillalsoexplode,throwingoutalargeamountofmattertorestoretheinternalbalance.Duetotheendothermicreactionofthenuclearfusionoftheheavierelements,thestarcollapsessharply,causingaviolentexplosion.Aftertheexplosion,somestarsallcollapsed,andsomestarsleftapartofthemattertobecomehigh-densitystars.
5)High-densitystage,thisisthedecayperiodofthestar.Thecentralpartleftbyanovaorsupernovaaftertheexplosionwillshrinkintovarioushigh-densitystars.Amongthem,thesmallermassshrinkstobecomeawhitedwarf,andthewhitedwarfglowsbycoolinguntiltheheatisdissipatedandbecomesanon-luminousblackdwarf.Ifthemassleftaftertheexplosionislarge,itwillshrinkintoaneutronstar,andevenevolveintoablackhole.
(3)Theevolutionoftheearth
1)Theearthwasborn4.6billionyearsago,afterthe"astronomicalperiod",thatis,thediffusematerialshrinksintotheoriginalearthandenterstheinnercircleoftheearthTheperiodofformationandevolutionthenentersthe"geologicalperiod",thatis,theperiodofcrustalmovementandland-seachanges.Duringthemeltinganddifferentiationoftheprimitiveearth,thematerialdominatedbyheavyelementssinkstoformthecore,andthelightermaterialfloatsuptoformthemantle.Thenthemantledifferentiatesintolightermaterialstoformthecrust,resultinginthespherestructure.
2)Intheprocessofmeltinganddifferentiationintheearth,alargeamountofgasescapesthesurfacetoformaprimitiveatmosphere.Duetotheeffectsofsolarradiation,ultravioletrays,etc.,theprimitiveatmospheregraduallyevolvedintoanatmospheredominatedbynitrogenandoxygen.Alargeamountofwatervaporcontainedintheprimitiveatmospherecondensed,formingtheprimitivehydrosphere,andgraduallyformingtoday'srivers,lakesandseas.
3)Aftertheformationoftheearth'scrust,itcontinuestomove.Modern"platetectonics"believesthattheentirecrustcanbedividedintoseveralplates,which"float"onthemantleasthenosphereandmoveslowly.Theconstantchangesintherelativepositionsoftheplateshavecausedthecontinentstodrift,formingthepatternofdistributionintoday'scontinentsandoceans.Themutualsqueezebetweentheplatescausedtheearth'scrusttomovevertically,causingtheupliftofthemountains.Platesalsocomeandgo.
Inthestudyofmoderncosmology,thecontributionsofStephenandHawkingshouldbeparticularlymentioned.HawkingisconsideredtobethemostoutstandingtheoreticalphysicistafterEinsteinintheworldtoday.Bornin1942,hewasconfinedinawheelchairfor20yearsduetoamyotrophiclateralsclerosis.Becausehefirmlybelievesthatwecanfullyunderstandtheuniverse,"strugglingtofindacompleteunderstandingisalwaysfarmorethandespairofthehumanspirit."Itisthisspiritofexplorationthatenableshimtolearnaboutgalaxyblackholes,quarks,thegrandunifiedtheory,antimatter,""TimeArrow"andotherin-depthdiscussions.Heappliedthemethodsofquantumtheorytotheprocessofformingblackholes.Itisprovedthatpurequantumparticlescanbeproducedintheblackholehorizon.Thisdiscoverybecamethefirstattempttounifythetheoryofrelativityandquantumtheory.Herevealedthatwhentheever-expandinguniversecollapses,timewillgoback,andhis"boundary"theoryoftheuniversemayreplacetheBigBangtheory.Hisseriesofinsightsarechangingpeople'sviewsontheuniverse.Therehavebeenverysharpcontroversiessurroundingthevarioustheoriesputforwardbymoderncosmology.Varioustheoriesofastrophysicshavetobedeveloped,andtheyneedtobetestedbynewfactsandtheoreticalargumentstodecidewhethertochoose.
Thefourmajorevolutions
Theevolutionoftheuniverse
(1)Opticalradiation
Itiscomposedofuniformandisotropichigh-density,high-temperatureandhigh-pressurematerials,andhasundergoneveryrapidexpansionandcoolingatanextremelyearlystage.About10^-37secondswhentheexpansionprogressed,aphasechangeoccurredthatcausedtheuniversetoinflate.Duringthisperiod,theexpansionoftheuniverseincreasedexponentially.Whentheinflationisover,thematterthatmakesuptheuniverseincludesquark-gluonplasmaandallotherelementaryparticles.
(2)Particleformation
Timescale-10^-43secondsTheuniverseemergesfromthequantumbackground.
Timescale-10^-35secondsThesamefieldisdecomposedintostrongforce,electroweakforceandgravitationalforce.
Thetimescaleis-10^-5seconds,10trillionKelvin,protonsandneutronsareformed.
Thetimescaleis0.0001seconds,andthetemperaturereachesseveraltensoftrillionKelvin,whichisgreaterthanthethresholdtemperatureofhadronsandleptons.Thecollisionofphotonsproducespositiveandnegativehadronsandpositiveandnegativeleptons.Atthesametime,someofthemareannihilatedintophotons.Whentheequilibriumstateisreached,thetotalnumberofparticlesisroughlyequaltothetotalnumberofphotons,andtheunannihilatedhadronsarebrokeninto"quarks".Atthistime,thequarksareina"progressivefreestate"withoutanyprotectiveeffect.Thetypesofparticlesintheuniverseare:positiveandnegativequarks,positiveandnegativeelectrons,andpositiveandnegativeneutrinos.Intheend,one-billionthofthepositiveparticlessurvived.
Thetimescaleis0.01secondandthetemperatureis100billionKelvin,whichislessthanthehadronthresholdtemperatureandgreaterthantheleptonthresholdtemperature.Thereactionofphotonstoproducehadronshasstopped.Hadronsarenolongerbrokenintoquarks,andprotonsandneutronseachaccountforhalf.However,duetothecontinuousannihilationofprotonsandneutrons,thenumberofhadronshasdecreased.Neutronsandprotonscontinuetotransformeachother.At1.09seconds,thetemperatureis10billionKelvin,proton:neutron=76:24
Thetimescaleis13.82seconds,andthetemperatureislessthan3billionKelvin.Thetaskofcreatingmatteriscompleted..Thephenomenonofneutrondecayoccurs,anditdecaysintoprotonspluselectronsplusantineutrinos.Atthistime,proton:neutron=83:17
Timescaleis3minutesand46seconds,temperatureis900millionKelvin,allantiparticlesareannihilated,photon:matterparticle=1billion:1,neutronnolongerdecays,Proton:neutron=87:13(untilnow);atthistime,averyimportantevolutionoccurred:aheliumnucleuswasgeneratedfrom2protonsand2neutrons,andtheneutronswerepreservedduetonuclearforces.Theuniversehasenteredtheageofnucleosynthesis.(Ifthereisnoheliumnucleusproduced,allneutronswilldecay,andtherewillbenootheratomicnucleiinthefuture)
Thetimescaleis300,000-700,000years,thetemperatureis4000-3000K,andtheenergyandmatterareinthermalequilibrium.Stablehydrogenandheliumnucleibegantoappear,andtheuniverseenteredtheeraofrecombination.Inthelaterperiod,theuniversegraduallytransformedintoaneradominatedbymatter.(Photonscantravelfreelyasthetemperaturedecreases,thatis,today's3Kcosmicbackgroundradiation!)
Thetimescaleis400-500millionyearsandthetemperatureis100K.Matterparticlesbegantocondense,andthegravitationalforcegraduallyincreased.Afterthe"darkage"passed,thefirststargalaxiesformed.
Stellarevolution
(1)Nuclearfusion
Atthebeginningoftheuniverse,therewasnomatterbutenergy.AftertheBigBang,matterconsistsofenergy.Converted(mass-energyconversionE=mc2),contemporaryparticlephysicstellsusthatatasufficientlyhightemperature(called"thresholdtemperature"),matterparticlescanbeproducedbythecollisionofphotons.
Withtheformationofthefirstbatchofstars,thenuclearfusionreactionofatomstookplaceinsidethestars,andthenthenucleiofelementssuchashelium,carbon,oxygen,magnesium,andironappeared.Nuclearfusionreferstotheformationofatomswithsmallmasses,mainlydeuteriumortritium.Undercertainconditions(suchasultra-hightemperatureandhighpressure),thenucleiwillaggregatewitheachothertogeneratenewandheaviernuclei,accompaniedbyhugeenergy.Aformofnuclearreactionreleased.(Itisworthnotingthatstarsofdifferentmassescancausedifferentdegreesofnuclearfusion.Thesunismainlyhydrogen-heliumfusion.Theheavieroneswilltriggercarbon-oxygen-magnesiumfusion,andtheheavieroneswilltriggerthenextroundoffusion.Thesimplesequenceis:hydrogen-helium-carbon-oxygen-magnesium-silicon-iron.However,nomatterhowmanystarsare,thefinalfusionresultcanonlybeiron,andtherecanbenonucleiheavierthanironinthestars!)AnythingontheperiodictableSome(exceptforman-madeelements)areformedinthestellarfurnace,andtheatomicnucleiafterironcanonlybeproducedinsuperexplosions.
(2)Theformationofgalaxies
Atthebeginningoftheuniverse,therewereverywidediffusenebulaedistributedintheuniverse.Thesenebulaewereundertheactionofuniversalgravitation.Graduallybegintoshrink,formingalotofgravitationalcentersfirst.Thesegravitationalcentersareofdifferentsizesanddistancesarealsodifferent.Sothesurroundingmatterbeginsto"fall"towardthesegravitationalcenters.Duringtheprocessofnebulamatterfallingtowardacertaingravitationalcenter,becauseThefallingdirectionisdisturbedbyothergravitationalcenters,notthe"centerofthesphere"pointingtothisgravitationalcenter,soangularmomentumisgenerated.Intheprocessoffalling,duetotheconservationofangularmomentum,thesesubstancesfallwhilerotating,thusformingOnebyonespiralgalaxyorbarredspiralgalaxy.Asforellipticalgalaxies,theyarehuge,oldgalaxiesformedafterthecollisionandmergerofspiralgalaxies.Thereisonlynebulamatterintheoriginallyformedgalaxy.Thefirststarsinthegalaxyareformedbyshrinkingandshrinkingduringtheformationofthegalaxy.Aftertheformationofthegalaxy,alargeproportionofthemattercomposingthegalaxyisstillinthestateofanebula,suchastheMilkyWay.Therearestillmanydiffusenebulaeinthespiralarmsof,andstarshavenotyetformed.
Earthevolution
(1)Astronomicalperiod
About4.6billionyearsago,thegravitycontractionandUndertheactionofradioactivedecayandheat,thematerialsinsidetheearthhavealsochanged,andsomematerialshavebeenlocallymelted.
(2)Geologicalperiod
Thelithosphere:undertheactionofgravity,theheaviermaterialoriginallyoutsidetheearthbeginstosinkslowly.Heavyelementssuchasliquidironsinktothecenteroftheearth,formingthecoreoftheearth.Atthesametime,thelightermatterinsidetheearthrose,graduallyformingthecrust,mantle,coreandotherspheres.
Aerosphere:Theformationoftheearth’satmosphereisimmediatelyfollowed.Intheearlydaysoftheformationoftheearth,alltheprimitiveatmosphereranintotheouterspace.Later,thetemperatureontheearthrose,thematerialinsidetheearthrecombined,andthegasinsidetheearthalsorosetotheground,formingtheearth'satmosphere.Thislayerofatmospherehasbeenfurtherdevelopedaftertheemergenceofgreenplants.Undertheinfluenceofgreenplantphotosynthesis,itgraduallydevelopedintoamodernatmosphere.
Hydrosphere:Atthebeginningoftheformationoftheearth,alargenumberofsmallcelestialbodieskepthittingtheearthataspeedof10kilometerspersecond,causingtheearth’snewlyformedcrusttoruptureagainandagain,causingtectonicactivities,Volcaniceruptionsoccurfrequently,andalargenumberofvolcanicjetsentertheskyabovetheearthtoformasecondaryatmosphere.TheatmosphereisfullofCO2,showingayellow"sky"withoutoxygen.Asthetemperatureoftheearthgraduallydrops,theatmosphereabovetheearthcondensesintowaterdroplets,whichformrainfallundertheactionofgravity.Thefirstrainonthisearthhasbeenundergroundendlesslyforthousands,tensofthousands,orevenmillionsofyears.Thepotholesandvalleysontheearth’ssurfacehavebecomerivers,lakesandseas,butthewateratthattimewasscorchinghotontheearth’ssurface.Boilingwater.
Biosphere:Onlywhenthereiswatercantherebelife.TheoldestlifeonEarthdiscovered,3.8billionyearsago.Upto3.5billionyearsago,bluealgaecapableofphotosynthesisappeared.Primitivelifehasstruggledformorethan2billionyearsinthelackofoxygenandboilingwater,transformingtheprimitiveocean,thusaffectingtheprimitiveatmosphere.Finally,about1.7billionyearsago,themodernoceanandmodernatmosphereformed.Thehydrosphereandatmospherefeedbackorganisms,whichmakeslifeontheplanetevolverapidlyfromlow-leveltohigh-level.By400millionyearsago,terrestrialplantsappeared,andthenanimalslanded,theearth'ssurfacewascoveredbylivingthings,andatruebiospherewasformed.Atthispoint,thethreeoutercirclesoftheearthfinallyformed.
Biologicalevolution
(1)Smallorganicmolecules
Theatmosphereisformedunderlightning,ultraviolet,shockwaves,raysandotherenergysources.Aseriesoforganicsmallmoleculecompounds,suchasaminoacids,nucleotides,etc.(thishasbeenconfirmedbytheexperimentofthesynthesisofinorganicsubstancesintoorganicsubstancesbyasparkdischargedevicedesignedbyAmericanscientistMillertosimulatethunderandlightning).
(2)Organicmacromolecules
Organicsmallmoleculecompoundseitherdirectlyfallintotheprimitiveocean,orconvergeintotheprimitiveoceanvialakesandrivers.Themiddlelayeraccumulatesandinteractsforalongtime,andunderappropriateconditions,itisfurthercondensedintobiologicalmacromoleculessuchasproteinsandnucleicacidswithprimitivestructuresandnon-specificfunctions.Thesebiologicalmacromoleculesaccumulateintheprimitiveocean,withincreasingconcentrationsandcondensingintodroplets.,Formingamulti-molecularsystem.
(3)Biologicalmacromolecules
Undercertainevolutionaryprobabilityandsuitableenvironmentalconditions,afteralongperiodofcontinuousevolution,about3.5billionyearsQianfinallyformedaprimitivelifeformwithmetabolismandself-reproductionability.Thisisthefirststageoflifeevolution,thatis,thenon-cellularlifestage,whichrealizestheprocessoftransitionfromnon-lifetolife.
(4)Primitiveorganisms
Fromabout3billionyearsagoto570millionyearsago,theearthenteredthepre-paleozoicperiod.Althoughthisperiodlastedforalongtime,andtheatmosphere,water,andbiospherealsodevelopedgreatly,theevolutionofthebiologicalworldwasveryslow.Untiltheendofthepre-paleozoicera,therewereonlyfungi,algaeandsomelow-gradeprotozoaontheearth.,Brachiopods,etc.About1.4billionyearsago,thedevelopmentofthebiologicalworldhasenteredthesecondstage,thatis,theprokaryoticcellstage.Inthisstage,lifealreadyhasacellshapeandarealcellmembrane,butthereisnorealnucleus,andtherealnuclearmembraneandtherealnuclearmembranecannotbedistinguished.Nucleolus.Itismainlyrepresentedbycyanobacteriathatwasmostprevalentbetween2.8to2billionyearsago.Itcancarryouttruephotosynthesis,absorbcarbondioxide,andreleaseoxygen,sothatthereducingatmosphereoftheearlyEarthisgraduallyreplacedbyanoxidizingatmosphere,andthenitentersintoInthethirdstageofevolution,eukaryoticcellsemerged.Thedevelopmentfromprokaryoticcellstoeukaryoticcellsisthemostimportantevolutioncompletedinthebiologicalworld.
(5)Biologicalevolution
Theevolutionaryhistoryofmodernorganismsclassifiedaccordingtothephylum,family,generaandspecies.
Structuralchemistryandpolymerchemistry
Whatisstructuralchemistry
Structuralchemistryisthestudyoftherelationshipbetweentheconfigurationandcompositionofsubstancesandmoleculesattheatomic-molecularlevelAswellasthechemicalsub-disciplineoftheinteractionofstructureandvariousmovements.Itisalsoabasicsubjectexpoundingtheinterrelationshipbetweenthemicrostructureofmatteranditsmacroscopicproperties.Structuralchemistryisnotonlycloselyrelatedtootherchemistrydisciplines,butalsointerrelated,coordinated,andpromotedwiththeresearchofvariousdisciplinessuchasbiologicalsciences,geologicalsciences,materialssciences,andmedicine.
Forchemistry,theresultsofatomicstructureresearchfirstgaveanewinterpretationoftheperiodiclawofelements.Mendeleev'speriodiclawbegantorevealtheinternalconnectionbetweenelements,butwhythepropertiesoftheelementschangeperiodicallywiththeincreaseofatomicweight?Thebasisforthisinternalconnectionisnotclear.WhentheinternalstructureoftheatomisrevealedandX-raysando-raysareusedasdetectionmethods,thesituationisdifferent.In1913,theBritishMosley(1887-1915AD)useddifferentelementsastargetsforgeneratingX-raysanddiscoveredthatthecharacteristicX-raystheyproducedhaddifferentwavelengths.HearrangedtheelementsaccordingtothewavelengthofthecharacteristicX-raysproduced,andfoundthatthearrangementorderisconsistentwiththeorderoftheelementsintheperiodictable.Hecalledthisordertheatomicnumber.In1920,theBritishChadwick(1891-1974)furthermadedifferentelements.Scatteringexperiments,measuringthenuclearchargeofeachelement,provethattheatomicnumberisexactlyequaltothenuclearchargeinnumber.Inotherwords,theperiodicityofanelementisnotbasedontheapparentatomicweight,butontheinternalstructureoftheatom,thatis,thechargeonthenucleus.By1925,duetotheemergenceofquantummechanicsandthePauliexclusionprinciple,theperiodiclawoftheelementsreceivedamorescientificexplanation.Peoplerealizethatelectronsoutsidethecorearedistributedaccordingtoacertainshell,andtheinnermostelectronshellcanonlyhold2electrons,andthendistributedaccordingtoacertainlaw.Themoreelectronlayers,thefarthertheoutermostelectronsarefromthecore,andtheattractiontoitThesmallertheforce,theeasieritistoloseelectrons;thefewertheouterelectrons,theeasieritistoloseelectrons;themoretheoutermostelectrons,theeasieritistocaptureelectrons.Whenitreaches8electrons,itissaturated;thenumberofouterelectronsisthesameThechemicalpropertiesoftheelementsaresimilar,theouterelectronsincrease,andthemetallicityoftheelementsdecreases.
Mankindproposedtheconceptofatomicvalencetounderstandthehistoricalprocessofchemicalbonds
Theconceptofatomicvalencehasbeenestablishedinthe19thcentury,buttheconceptofatomicvalenceatthattimeisstillamoreintuitivedescription.Howdoesitworkwithacertainvalence,anditisnotreallyunderstoodhowtheyarecombinedwitheachother.
(1)Afterthediscoveryofelectrons,peoplerealizedthatthepositivevalenceofanatomisthenumberofelectronsthatanatomloseswhenitiscombined;whilethenegativevalenceisthenumberofelectronsanatomgets.Itispeople'sfurtherunderstandingoftheconceptofatomicvalence.
(2)In1916,theGermanchemistKossel(1888-1956)developedtheatomicvalencetheoryundertheinfluenceofBohr'satomicstructuremodel.Hebelievesthatatomsloseelectronsorgainelectronstoachieveanelectronicstructuresimilartoinertelements,formingstableions.Someofthesestableionsloseelectronsandbecomepositive;theotherpartloseelectrons.Theyarenegativelycharged,andtheseionswithpositiveandnegativechargesarecombinedwitheachotherduetoCoulomb'sgravitationalforce.KosselcalledthisvalencebondbetweenpositiveandnegativeionsformedbyCoulomb'sgravitationalforceasanelectricvalencebond.
(3)In1916,AmericanchemistLewis(1875—1946AD)putforwardthetheoryofcovalentbonds.
(4)Brand-newchemicalbondconcept,"electroniccloud".
(5)Valencebondtheory,theotheriscalledmolecularorbitaltheory.
(6)Paralleltothevalencebondtheory,themolecularorbitalmethodisusedtostudythemolecularbondforce.
Afterenteringthe20thcentury,thenaturallawsofmicro-objectshavebeencontinuouslyrevealed,andexperimentalmethodshavechangedwitheachpassingday.Asaresult,theentirechemistryhaschangedthefaceofthefactoryandformedalargefamilywithmanybranches.Tounderstandthecompositionandstructureofsubstances,chemicalanalysisisnecessary.
Withthedevelopmentofvarioussciencesandtechnologiesinthe20thcentury,especiallythedevelopmentofopticsandelectricity,chemicalanalysismethodshavechangedrapidly,providingaprerequisiteformorequantitativeandprecisechemicalresearch.Thewideapplicationofopticalanalysismethods(includingspectroscopicanalysisandphotometricanalysis),chromatography(includingchromatography,tomography),andelectrochemicalanalysishavemadechemicalanalysisdevelopedfromthemacroscopictothemicroscopic,andfromtheoveralltoThemicroscopicareaextendsfromthewholetothesurfaceandthethinlayer,andstretchesfromthestaticstatetothedynamicstate.Thecontentoftheanalysishasfarexceededthecompositionofasimplesubstance,andinvolvedtheinternalstructureofthesubstance.
Theestablishmentofsyntheticorganicchemistryandpolymerchemistry
Duetothedevelopmentofthechemicalindustry,humanshavenotonlyextractedorganicsubstancesfromnaturalproducts,agriculturalproducts,coal,andcoaltar,butalsoin20Inthecentury,variousorganiccompoundscouldbeproducedfromcalciumcarbide,petroleum,etc.asrawmaterials.Inaddition,simpleorganicmoleculescanbeusedtoartificiallyproduceavarietyofsyntheticdyes,syntheticfibers,syntheticdrugs,syntheticrubber,syntheticplastics,syntheticproteinsandotherpolymercompounds,formingahigh-levelstudyoftherelationshipbetweenthestructureandperformanceofmacromolecules.Molecularscience.
Foralongtime,peoplehavebelievedthatcellulose,starch,protein,etc.areformedbytheassociationofmanysmallmoleculeswithringstructures.Until1920,theGermanchemistStaudinger(1881-1965)Thecycliccompoundisdistinguishedfromthelong-chainpolymercompound,whichprovesthatnaturalrubber,cellulose,etc.arenotthephysicalassociationofmultiplecyclicsmallmolecules,butlargemoleculeswithachainstructureandahighmolecularweight.However,theconceptofmacromoleculeswasnotimmediatelywidelyacceptedatthattime,andmanychemistsstillsupportedtheideaofcyclicstructure.By1930,becauseStaudinger,SwedishchemistSvidberg(1884AD)andothersdeterminedthemolecularweightofpolymers,AmericanchemistCarozes(1896-1937AD)passeddibasicacidandglycolThesynthesisofpolymerfiberfilamentswithamolecularweightofabout20,000,confirmedthetheoryofpolymerlong-chainstructure.Inthe1930s,chemistsestablishedastructuralmodelofpolymercrystals,putforwardthestatisticaltheoryofpolymerlongchainsandthetheoryofmolecularmotion,andsynthesizedvitaminsA,B2,C,D,E,Kandsyntheticresins.Wait.Theapplicationofnuclearmagneticresonanceandtheinventionofelectronmicroscopyhaveenabledtheresearchofmodernpolymerchemistrytoachievemoreresults,andtherehavebeenalargenumberofhigh-efficiencycatalysts,high-strengthpolymermaterialswithspecialfunctions.Theinterpenetrationbetweenpolymerchemistryandbiologyhasmadegreatprogressinbiochemistry.
In-depthbiologicalresearchfromthecellularleveltothemolecularlevel
1.Thetheoryofspeciesevolution,thelawofinheritance,andthetheoryofgenesareimportantdiscoveriesinbiologyinthe19thcentury.Sincethebeginningofthe20thcentury,farming.Thedirectionalbreedingofhigh-qualityspecies,theapplicationofbiologicalhormones,thediagnosis,preventionandcontrolofgeneticdiseasesandtumors,andtheresearchontheresistanceofpathogensallrequirein-depthexplanationsintheoryandeffectivemeasuresinpractice.Learningfromthemacro-qualitativeinvestigationintoitsmicro-quantitativeexplorationfield,soastofindouttheinternalmechanismofbiologicalevolution,heredityandmutation.
(1)In1909,AmericanbiologistMorgan(1866-1945AD)proposedthegenetheoryonthebasisofMendeliangenetics,whichregardedgenesassphericalparticleslocatedonchromosomes.Genesarefunctionallythesmallestunitthatdeterminesthetrinityofdifferences,mutationsandrecombinationofgenetictraits.
(2)Attheendofthe19thcenturyandthebeginningofthe20thcentury,intheinterpenetrationofbiochemistry,biophysics,bacteriology,virology,etc.,anewscience-molecularbiologywasborn.
(3)Sincethediscoveryofthecellinthe19thcenturyandtakingitasthebasicunitoflife,peoplehavebeguntostudythestructureandfunctionofthecell.2.Researchonlifephenomenaatthemolecularlevel
Theresearchonlifephenomenaatthemolecularlevelandthebirthofmolecularbiologyaremainlythefollowingdiscoveries:
First,Usingexperimentalmethodstorevealtherelationshipbetweengenesandenzymes.
Theyirradiatedtheredbreadmoldwithraysandultravioletraystocausemutationsinsomeoftheirgenes,andthenexploredtheeffectofgeneticchangesonthenutritionalrequirementsofthemold.Theredbreadmoldcangrowinamediumcomposedofsugar,saltandanauxin,butsomemutantredbreadmoldsobtainedbyirradiationlosetheirgrowthability.Thisisbecausethemutanthasdestroyedthegeneoftheenzymethatmakesarginine,andwithoutthiskindofmold,themoldcannotproducethearginineitneedsandcannotgrow.Afteralotofresearch,theyhaveobtainedanewconceptintherelationshipbetweengenesandtraitdevelopment:nomatterwhattraitsageneaffects,itfirstdeterminesenzymes,enzymesdeterminemetabolism,andmetabolismdeterminesvarioustraits.Basedonthis,Biddleproposedthe"onegene,oneenzyme"theory.Itshowsthattherelationshipbetweengenesandhereditarytraitsisnotdirectlycorrespondingasoriginallythought.Eachgeneworksthroughaspecialenzyme,orgenesworkthroughtheregulationofcertainchemicalprocesses.The"onegene,oneenzyme"theorydescribestherelationshipbetweenheredityandmetabolicprocesses,whichleadspeopletoimaginethatgenesareatemplatefortheformationofenzymes.
Second,aboutthediscoverythatDNAisacarrierofgeneticinformation.
In1944,threeAmericanbiochemistsAvery(1861-1955AD)andMcLeod(AD1909-)McCarty(AD1911-)collaboratedtofindapneumococcalstrainExtractingDNAandtransferringittoanothertypeofbacteriaprovesthatonetypeofbacteriahasacquiredthegeneticcharacteristicsoftheprevioustypeofbacteria,therebyindicatingthatDNAmaybethechemicalandphysicalbasisofgenetictraits.Thisdiscoveryhasfar-reachingsignificance,ithasarousedmorepeople'sinterest,butalsoarousedsomepeople'ssuspicion.DelbruckoftheUnitedStates(1906-AD),whocametotheUnitedStatesfromItaly,LuriaandHorch(1908-),alsoformedaphageresearchteaminthe1940s.TheyfoundthatasinglephageenteredE.coli.Replicateitself100timesinhalfanhour.In1952,Holschetal.usedisotopelabelingmethodstofindthatonlytheDNApartofthephageinvadedandreproducedparasiticbacteria,whiletheproteincoatremainedoutsideofE.coli.ThisexperimentmoreclearlyprovesthatDNAcarriesalltheinformationofphageself-replication,andDNAisthecarrierofgeneticinformation(geneticinformationreferstothesequenceofbasesinDNA).
Third,thedoublehelixstructureofDNAmolecules.
ResearchonthemolecularstructureofDNAisbeingcarriedoutseparatelyintheUKatthesametime.TheyareWilkinsofKingsCollegeLondon(AD1916-),femalescientistFranklin(AD1920-)andCambridgeWatson(AD1928-)andCrick(AD1916-)oftheUniversity.AmemberofWatson’soriginalAmericanbacteriophageresearchteam,helaterwenttotheUKtolearntoanalyzethecrystalstructureofproteinsbyX-raydiffraction;Crickoriginallystudiedphysics,butlaterbecameinterestedinbiologyandworkedonthesamewithWatson.Research.WatsonandCrickcametoaveryimportantconclusiononthebasisofanalyzingandstudyingtheinformationobtainedbyX-raydiffraction:DNAmoleculeiscomposedofdoublehelix,twophosphatesugarchainsformtheskeleton,andthroughaseriesofsynthesisThepairofnucleotidebases(adenineA,thymineT,cytosineC,guanineG)arelinkedbyhydrogenbonds,whereATandGCarepairedwitheachother,andeachsinglehelixformsitsowncomplementaryhelix.Thegeneticinformationisexpressedbythesequenceofnucleotides.ThebasicfeatureofthenucleotidesequenceisthatAiscomplementarytoT,andGiscomplementarytoC.Duetothiscomplementaryfeature,DNAcanreplicateonitsown.Therelationshipbetweenthedoublehelixstructureisliketherelationshipbetweenalockandakey.Whenseparated,eachcanformitsowncomplement,thusrebuildingallthedouble-strandedDNAmolecules.Ithaslongbeenknownthattheprocessofcelldivisionistopassthegeneticgenesofthemothercelltothedaughtercells,butnowitisexpressedthroughthestructureofDNA.ThediscoveryofthedoublehelixstructureofDNAiscalledthegreatestdiscoveryofbiologyinthe20thcenturyandisasignofthebirthofmolecularbiology.
Fourth,thefunctionofDNAandRNA
In1955,theSpanishAmericanOacho(1905-AD)andtheAmericanKongBo(1918-)firstusedenzymesThemethodartificiallysynthesizesDNAandRNA.Inthestudyofhowgenescontrolthesynthesisofaspecificproteinincells,FrenchbiochemistsJacob(1902-AD),Levov(1902-AD)andMono(1910-1976)discoveredthatAmessengerRNA(ormRNA)inthecellnucleusfurtherrevealsthefunctionsofDNAandRNA,andunderstandsthespecificprocessoftransmittinggeneticinformationtothenextgenerationthroughthereplicationofDNAmolecules.Inthisprocess,DNAonlyservesasatemplate,whichdeterminesthesequenceofnucleotidesinmRNA;whenmRNAissynthesized,theso-calledtranscriptioniscompleted,mRNAentersthecytoplasmfromthenucleus,andmRNAislikeamessengerthatbringssynthesisThecodeoftheprotein.Basedontheirresearchonbacteria(usuallyEscherichiacoli),Jacob,Monoandothershaveidentifiedthreegenesandestablishedamodelofhowtoquantitativelycontrolproteinsynthesisatthetranscriptionallevel.Atfirst,peoplethoughtthatafterDNAmoleculesreplicatedthemselves,theytranscribedgeneticinformationtomRNA,andmRNAtranslatedthegeneticinformationintoprotein.Thisdirectionwasirreversible,calledthecentrallaw.Later,peoplediscoveredthatthislawcannotbeabsolute.Insomecases,RNAcanalsobeacarrierofgeneticinformation,andgeneticinformationcanalsobetransmittedfromRNAtoDNA,whichiscalledtheanti-centrallaw.
Fifth,theadventofthegeneticcodetable
Thewayinwhichdifferentnucleotidesequencesdeterminethesequenceofdifferentaminoacidsiscalledthegeneticcode.AmericanbiochemistsHolly(1922-AD),Keana(1922-AD)andothersfirstmadeimportantcontributionstoelucidatingthegeneticcode;andtheAmericanscientistNilumbowasofgreatsignificancetothesubsequentdevelopment.Ge(1927-AD)andFrenchscientistMatthew,theydeterminedthegeneticcodeofvariousaminoacidsinthelaboratory.By1969,themeaningof64kindsofgeneticcodeshadbeentested,andthegeneticcodetablewaslisted.
3.Comprehensivetheoryofevolution
ThestudyoflifephenomenaatthemolecularlevelhasfurtherenrichedDarwin'stheoryofevolution,andmodernDarwinism,orthetheoryofcomprehensiveevolution,hasemerged.
After1900,MendeliansbegantoconductexperimentalresearchoncertainfactsofevolutionandcametoconclusionsthatweredifferentfromsomeprinciplesofDarwinism.Atthistime,notonlygeneticistsopposedDarwinism,butevenThosewithanevolutionaryviewalsobegantoattackDarwinism.Thiskindofcontroversyhasalreadyexisted.SoonafterDarwin's"OriginofSpecies"waspublishedin1859,in1864,GermanembryologistCrickellputforwardthetheoryofheterogeneousreproduction,opposingslowevolution,naturalselectionandstruggleforsurvival.Hebelievesthatevolutioniscarriedoutinaleapmodeundertheinfluenceoftheinternaldevelopmentoforganisms.Later,somepeopleformedamutationtheorybasedonexperimentsandobservationsoneveningprimrose.Theybelievedthathereditarycharacteristicsandtraitscouldsuddenlymutate,andnewspeciesweredevelopedbyleap.Itdoesnotdependontheinfluenceoftheexternalenvironment.ThesetheoriesareopposedtoDarwin'stheoryofslowevolutionthat"thereisnoleapinnature",andtheydenytheroleofnaturalselection.Theoppositionbetweengeneticsandevolutionisonlyatemporaryphenomenon.Withthedeepeningofresearch,theprocessofcombininggeneticsandevolutionhasbegun.
4.Evaluationofthecomprehensivetheoryofevolution:Thecomprehensivetheoryofevolutionnotonlyreaffirmsthegreatroleofnaturalselection,butalsousesnaturalselectiontoexplainmanyfactsthatclassicalDarwinismcannotexplain,andcompletelyoverturnsalloutdatedevolutionaryhypotheses.(Suchasacquiredinheritance,autogenesis,exogenousoccurrence,pre-selectionadaptation,etc.)andalltheoriesthatexplainevolutionwithacertainsinglefactor(mutation,geneticdrift,isolation,etc.).InthehistoricalprocessfromDarwin'stheoryofevolutiontothecomprehensivetheoryofevolution,onecanseethegeneralprocessofthedevelopmentofscientifictheories.People'sunderstandingoftheeffectsofmutationandnaturalselectionisalsodevelopinginaccordancewiththelawofaffirmation,negation,andnegationofnegation."Scienceisoriginallyadevelopingconcept,andscientifictheoriesarealsodeveloping.Thehistoryofscienceandtechnologyshowsthatinpeople'sunderstandingofnature,thereisnouniversaltruth(space)andalltimes(time).Theexistingscientifictheorieshaveroomforfurtherexploration.