Copyright © 2009 Pearson Education, Inc.Chapter 17The Beginning of TimeCopyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc.17.1 The Big BangOur goals for learning:• What were conditions like in the earlyuniverse?• What is the history of the universeaccording to the Big Bang theory?Copyright © 2009 Pearson Education, Inc.What were conditions like in theearly universe?Copyright © 2009 Pearson Education, Inc.The universemust havebeen muchhotter anddenser earlyin time.Estimating the Age of the UniverseCopyright © 2009 Pearson Education, Inc.The earlyuniverse musthave beenextremely hotand dense.Copyright © 2009 Pearson Education, Inc.Photons converted intoparticle–antiparticlepairs and vice versa.E = mc2The early universe wasfull of particles andradiation because of itshigh temperature.Copyright © 2009 Pearson Education, Inc.What is the history of the universeaccording to the Big Bang theory?Copyright © 2009 Pearson Education, Inc.Defining Eras of the Universe• The earliest eras are defined by the kindsof forces present in the universe.• Later eras are defined by the kinds ofparticles present in the universe.Copyright © 2009 Pearson Education, Inc.Four known forcesin universe: Strong Force Electromagnetism Weak Force GravityCopyright © 2009 Pearson Education, Inc.Thought QuestionWhich of the four forces keeps you from sinking to thecenter of Earth?A. GravityB. ElectromagnetismC. Strong ForceD. Weak ForceCopyright © 2009 Pearson Education, Inc.Thought QuestionWhich of the four forces keeps you from sinking to thecenter of Earth?A. GravityB. ElectromagnetismC. Strong ForceD. Weak ForceCopyright © 2009 Pearson Education, Inc.Four known forcesin universe: Strong Force Electromagnetism Weak Force GravityDo forces unify at high temperatures?Copyright © 2009 Pearson Education, Inc.Four known forcesin universe: Strong Force Electromagnetism Weak Force GravityDo forces unify at high temperatures?Yes!(Electroweak)Copyright © 2009 Pearson Education, Inc.Four known forcesin universe: Strong Force Electromagnetism Weak Force GravityDo forces unify at high temperatures?Maybe (GUT)Yes!(Electroweak)Copyright © 2009 Pearson Education, Inc.Four known forcesin universe: Strong Force Electromagnetism Weak Force GravityDo forces unify at high temperatures?Maybe (GUT)Yes!(Electroweak)Who knows?(String Theory)Copyright © 2009 Pearson Education, Inc.Planck EraTime: < 10-43 sTemp: > 1032 KNo theory of quantumgravityAll forces may havebeen unifiedCopyright © 2009 Pearson Education, Inc.GUT EraTime: 10-43–10-38 sTemp: 1032–1029 KGUT era began whengravity became distinctfrom other forces.GUT era ended whenstrong force becamedistinct fromelectroweak force.Copyright © 2009 Pearson Education, Inc.Electroweak EraTime: 10-10–10-10 sTemp: 1029–1015 KGravity became distinctfrom other forces.Strong, weak, andelectromagnetic forcesmay have been unifiedinto GUT force.Copyright © 2009 Pearson Education, Inc.Particle EraTime: 10-10–0.001 sTemp: 1015–1012 KAmounts of matter andantimatter are nearlyequal.(Roughly one extraproton for every 109proton–antiprotonpairs!)Copyright © 2009 Pearson Education, Inc.Era of NucleosynthesisTime: 0.001 s–5 minTemp: 1012–109 KBegan when matterannihilates remainingantimatter at~ 0.001 s.Nuclei began to fuse.Copyright © 2009 Pearson Education, Inc.Era of NucleiTime: 5 min–380,000 yrsTemp: 109–3000 KHelium nuclei formed atage ~3 minutes.The universe became toocool to blast heliumapart.Copyright © 2009 Pearson Education, Inc.Era of AtomsTime: 380,000 years–1billion yearsTemp: 3000–20 KAtoms formed at age~380,000 years.Background radiation isreleased.Copyright © 2009 Pearson Education, Inc.Era of GalaxiesTime: ~1 billionyears–presentTemp: 20–3 KThe first stars andgalaxies formed by~1 billion years afterthe Big Bang.Copyright © 2009 Pearson Education, Inc.Primary Evidence for the Big Bang1. We have detected the leftover radiationfrom the Big Bang.2. The Big Bang theory correctly predicts theabundance of helium and other lightelements in the universe.Copyright © 2009 Pearson Education, Inc.What have we learned?• What were conditions like in the early universe?— The early universe was so hot and so dense thatradiation was constantly producingparticle–antiparticle pairs and vice versa.• What is the history of the universe according tothe Big Bang theory?— As the universe cooled, particle production stopped,leaving matter instead of antimatter.— Fusion turned the remaining neutrons into helium.— Radiation traveled freely after the formation ofatoms.Copyright © 2009 Pearson Education, Inc.17.2 Evidence for the Big BangOur goals for learning:• How do we observe the radiation left overfrom the Big Bang?• How do the abundances of elements supportthe Big Bang theory?Copyright © 2009 Pearson Education, Inc.How do we observe the radiationleft over from the Big Bang?Copyright © 2009 Pearson Education, Inc.The cosmicmicrowavebackground—the radiation leftover from theBig Bang—was detected byPenzias andWilson in 1965.Copyright © 2009 Pearson Education, Inc.Background radiation from the Big Bang has beenfreely streaming across the universe since atomsformed at temperature ~3000 K: visible/IR.Creation of the Cosmic Microwave BackgroundCopyright © 2009 Pearson Education, Inc.Expansion of the universe has redshifted thermalradiation from that time to ~1000 times longerwavelength: microwaves.Background has perfectthermal radiationspectrum at temperature2.73 K.Copyright © 2009 Pearson Education, Inc.Full Sky in All WavelengthsCopyright © 2009 Pearson Education, Inc.WMAP gives us detailed baby pictures of structure inthe universe.Copyright © 2009 Pearson Education, Inc.How do the abundances of elementssupport the Big Bang theory?Copyright © 2009 Pearson Education, Inc.Protons and neutrons combined to make long-lasting heliumnuclei when the universe was ~5 minutes old.Copyright © 2009 Pearson Education, Inc.Big Bang theory prediction: 75% H, 25% He (by mass)Matches observations of nearly primordial gasesCopyright © 2009 Pearson Education, Inc.Abundances ofother lightelements agreewith Big Bangmodel having4.4% normalmatter—moreevidence forWIMPS!Copyright © 2009 Pearson Education, Inc.Thought QuestionWhich of these abundance patterns is an unrealisticchemical composition for a star?A. 70% H, 28% He, 2% otherB. 95% H, 5% He, less than 0.02% otherC. 75% H, 25% He, less than 0.02%
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