cosmic microwave background radiation

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1、CosmicmicrowavebackgroundradiationLymanPageandDavidWilkinsonPhysicsDepartment,PrincetonUniversity,Princeton,NewJersey08544Thecosmicmicrowavebackgroundradiation(CMBR)iswidelyinterpretedasthethermalafterglowofahotbigbang.MeasurementsoftheCMBRintensityasafunctionoffrequencycons

2、trainthehistoryofcosmicenergetics.MeasurementsoftheanisotropyintheCMBRtemperatureprovideasnapshotofthedistributionof¯uctuationsinthegravitationalpotentialattheearlieststagesofcosmicstructureformation.TheauthorsreviewtheinterpretationoftheCMBRemphasizingthestatusofcurrentobse

3、rvationsandfutureobservationalprospects.OurknowledgeoftheCMBRwilldramaticallyincreaseinthe®rstdecadeofthetwenty-®rstcentury.[S0034-6861(99)05202-2]I.INTRODUCTIONII.MEASUREMENTSOFTHECMBRMostastronomersandphysicistsnowbelievethatweA.Thespectrumliveinanexpandinguniversethatevol

4、vedfromanearlyThetemperatureoftheCMBRcanbeestimatedbystateofextremelyhighdensityandtemperature.Mea-notingthatasubstantialfraction('24%)ofthemattersurementsofthespectrumandanisotropyofthecosmicintheuniverseisheliumandassumingthatitwasmademicrowavebackgroundradiation(CMBR)prov

5、idebynuclearreactionsintheearlyuniverse.Ifso,atanagestrongevidencesupportingthispicture.Today,thespec-oft'100s,whileneutronswerestillaround,atempera-trumoftheCMBRmatchesthatofa2.728Kblackbodytureof109Kandabaryondensityof1027m23wouldtowithin0.01%,andtheradiationishighlyisotro

6、picongeneratetheobservedHeabundance.Themeanbaryondensitytodayofabout1m23givesanexpansionfactorthesky.Bothofthesepropertiesareexpectedoftheof109andatemperatureof1K.Thisroughestimatethermalradiationremnantofahot,denseearlyuniverse(Peebles,1993).meansthattheCMBRisinthemicrowave

7、band.TheessentialingredientsofanexperimenttomeasureThecartooninFig.1showshowtheCMBRevolvestheCMBRtemperatureatagivenwavelengthare(1)anastheuniverseexpandsandcools.Localthermalequi-antenna(usuallyahorn)withverylowside-lobere-libriumisestablishedintheradiationepochbyradiatives

8、ponse,(2)acoldemitterofknowntemperature(calledscatteringprocesses,bremsstra