Copyright © 2009 Pearson Education, Inc. Chapter 17 The Beginning of TimeCopyright © 2009 Pearson Education, Inc. Do you believe that science will ever understand the beginning of the Universe? A. Yes B. NoCopyright © 2009 Pearson Education, Inc. Flip a coin A. Heads B. TailsCopyright © 2009 Pearson Education, Inc. Give your clicker to someone else. Flip a coin A. Heads B. TailsCopyright © 2009 Pearson Education, Inc. Flip again. Now answer the question – Do you share your clicker or click for someone else? • If Heads – tell the truth • If tails – lie! A. I have only used my clicker B. I have clicked for a friend.Copyright © 2009 Pearson Education, Inc.Copyright © 2009 Pearson Education, Inc. 17.1 The Big Bang Our goals for learning: • What were conditions like in the early universe? • What is the history of the universe according to the Big Bang theory?Copyright © 2009 Pearson Education, Inc. What were conditions like in the early universe?Copyright © 2009 Pearson Education, Inc. The universe must have been much hotter and denser early in time. Estimating the Age of the UniverseCopyright © 2009 Pearson Education, Inc. The early universe must have been extremely hot and dense.Copyright © 2009 Pearson Education, Inc. Photons converted into particle–antiparticle pairs and vice versa. E = mc2 The early universe was full of particles and radiation because of its high temperature.Copyright © 2009 Pearson Education, Inc. What is the history of the universe according to the Big Bang theory?Copyright © 2009 Pearson Education, Inc. Defining Eras of the Universe • The earliest eras are defined by the kinds of forces present in the universe. • Later eras are defined by the kinds of particles present in the universe.Copyright © 2009 Pearson Education, Inc. Four known forces in universe: Strong Force Electromagnetism Weak Force GravityCopyright © 2009 Pearson Education, Inc. Thought Question Which of the four forces keeps you from sinking to the center of Earth? A. Gravity B. Electromagnetism C. Strong Force D. Weak ForceCopyright © 2009 Pearson Education, Inc. Thought Question Which of the four forces keeps you from sinking to the center of Earth? A. Gravity B. Electromagnetism C. Strong Force D. Weak ForceCopyright © 2009 Pearson Education, Inc. Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Do forces unify at high temperatures?Copyright © 2009 Pearson Education, Inc. Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Do forces unify at high temperatures? Yes! (Electroweak)Copyright © 2009 Pearson Education, Inc. Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Do forces unify at high temperatures? Maybe (GUT) Yes! (Electroweak)Copyright © 2009 Pearson Education, Inc. Four known forces in universe: Strong Force Electromagnetism Weak Force Gravity Do forces unify at high temperatures? Maybe (GUT) Yes! (Electroweak) Who knows? (String Theory)Copyright © 2009 Pearson Education, Inc. Planck Era Time: < 10-43 s Temp: > 1032 K No theory of quantum gravity All forces may have been unifiedCopyright © 2009 Pearson Education, Inc. GUT Era Time: 10-43–10-38 s Temp: 1032–1029 K GUT era began when gravity became distinct from other forces. GUT era ended when strong force became distinct from electroweak force.Copyright © 2009 Pearson Education, Inc. Electroweak Era Time: 10-10–10-10 s Temp: 1029–1015 K Gravity became distinct from other forces. Strong, weak, and electromagnetic forces may have been unified into GUT force.Copyright © 2009 Pearson Education, Inc. Particle Era Time: 10-10–0.001 s Temp: 1015–1012 K Amounts of matter and antimatter are nearly equal. (Roughly one extra proton for every 109 proton–antiproton pairs!)Copyright © 2009 Pearson Education, Inc. Era of Nucleosynthesis Time: 0.001 s–5 min Temp: 1012–109 K Began when matter annihilates remaining antimatter at ~ 0.001 s. Nuclei began to fuse.Copyright © 2009 Pearson Education, Inc. Era of Nuclei Time: 5 min–380,000 yrs Temp: 109–3000 K Helium nuclei formed at age ~3 minutes. The universe became too cool to blast helium apart.Copyright © 2009 Pearson Education, Inc. Era of Atoms Time: 380,000 years–1 billion years Temp: 3000–20 K Atoms formed at age ~380,000 years. Background radiation is released.Copyright © 2009 Pearson Education, Inc. Era of Galaxies Time: ~1 billion years–present Temp: 20–3 K The first stars and galaxies formed by ~1 billion years after the Big Bang.Copyright © 2009 Pearson Education, Inc. Primary Evidence for the Big Bang 1. We have detected the leftover radiation from the Big Bang. 2. The Big Bang theory correctly predicts the abundance of helium and other light elements 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 that radiation was constantly producing particle–antiparticle pairs and vice versa. • What is the history of the universe according to the 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 of atoms.Copyright © 2009 Pearson Education, Inc. 17.2 Evidence for the Big Bang Our goals for learning: • How do we observe the radiation left over from the Big Bang? • How do the abundances of elements support the Big Bang theory?Copyright © 2009 Pearson Education, Inc. How do we observe the radiation left over from the Big Bang?Copyright © 2009 Pearson Education, Inc. The cosmic microwave background— the radiation left over from the Big Bang— was detected by Penzias and Wilson in 1965.Copyright © 2009 Pearson Education, Inc. Background radiation from the Big Bang has been freely streaming across the universe since atoms formed at temperature ~3000 K: visible/IR. Creation of the Cosmic Microwave BackgroundCopyright © 2009 Pearson Education, Inc. Expansion of the universe has redshifted thermal radiation from that time to ~1000 times longer wavelength: microwaves. Background has perfect thermal radiation spectrum at temperature 2.73
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