1 Introduction to Cosmology The second edition of Introduction to Cosmology is an exciting update of this award-winning textbook. It is aimed primaril...

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Introduction to Cosmology The second edition of Introduction to Cosmology is an exciting update of this award-winning textbook. It is aimed primarily at advanced undergraduate students in physics and astronomy, but is also useful as a supplementary text at higher levels. It explains modern cosmological concepts, such as dark energy, in the context of the Big Bang theory. Its clear, lucid writing style, with a wealth of useful everyday analogies, makes it exceptionally engaging. Emphasis is placed on the links between theoretical concepts of cosmology and the observable properties of the universe, building deeper physical insights in the reader. The second edition includes recent observational results, fuller descriptions of special and general relativity, expanded discussions of dark energy, and a new chapter on baryonic matter that makes up stars and galaxies. It is an ideal textbook for the era of precision cosmology in the accelerating universe. Ba r ba r a Ry d e n received her PhD in astrophysical sciences from Princeton University, New Jersey in 1987. After postdocs at the Harvard-Smithsonian Center for Astrophysics and the Canadian Institute for Theoretical Astrophysics, she joined the astronomy faculty at The Ohio State University, where she is now a full professor. She has over twenty years of experience in teaching, at levels ranging from introductory undergraduate courses to advanced graduate seminars. She won the Chambliss Astronomical Writing Award for the first edition of Introduction to Cosmology (2002), and is the co-author, with Bradley Peterson, of Foundations of Astrophysics (2010).

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

Introduction to Cosmology Second Edition

Barbara Ryden The Ohio State University

© in this web service Cambridge University Press

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

University Printing House, Cambridge CB2 8BS, United Kingdom Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781107154834 © Pearson Education, Inc., 2003, Barbara Ryden 2017 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First edition published in 2002 by Pearson Education, Inc. Second edition published 2017 Printed in the United Kingdom by TJ International Ltd, Padstow, Cornwall A catalog record for this publication is available from the British Library. Library of Congress Cataloging-in-Publication Data Names: Ryden, Barbara Sue, author. Title: Introduction to cosmology / Barbara Ryden, The Ohio State University. Description: Second edition. | New York, NY : Cambridge University Press, 2017. | Includes bibliographical references and index. Identifiers: LCCN 2016040124 | ISBN 9781107154834 (Hardback ; alk. paper) | ISBN 1107154839 (Hardback ; alk. paper) Subjects: LCSH: Cosmology. Classification: LCC QB981 .R93 2016 | DDC 523.1–dc23 LC record available at https://lccn.loc.gov/2016040124 ISBN 978-1-107-15483-4 Hardback Additional resources for this publication at www.cambridge.org/cosmology Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party Internet Web sites referred to in this publication and does not guarantee that any content on such Web sites is, or will remain, accurate or appropriate.

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

For my husband

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

Contents

page xi

Preface 1 Introduction

1

2 Fundamental Observations

6

2.1

The Night Sky is Dark

6

2.2

The Universe is Isotropic and Homogeneous

9

2.3

Redshift is Proportional to Distance

12

2.4

Different Types of Particles

18

2.5

Cosmic Microwave Background

23

Exercises

25 27

3 Newton versus Einstein

3.1

The Way of Newton

28

3.2

The Special Way of Einstein

29

3.3

The General Way of Einstein

34

3.4

Describing Curvature

37

3.5

The Robertson–Walker Metric

41

3.6

Proper Distance

43

Exercises

47 49

4 Cosmic Dynamics

4.1

Einstein’s Field Equation

50

4.2

The Friedmann Equation

52

4.3

The Fluid and Acceleration Equations

58

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Contents

4.4

Equations of State

60

4.5

Learning to Love Lambda

63

Exercises

67

5 Model Universes

69

5.1

Evolution of Energy Density

69

5.2

Empty Universes

74

5.3

Single-component Universes

77

5.3.1

Matter only

80

5.3.2

Radiation only

81

5.3.3

Lambda only

83

5.4

5.5

Multiple-component Universes

84

5.4.1

Matter + Curvature

86

5.4.2

Matter + Lambda

90

5.4.3

Matter + Curvature + Lambda

92

5.4.4

Radiation + Matter

95

Benchmark Model

Exercises 6 Measuring Cosmological Parameters

96 100 102

6.1

“A Search for Two Numbers”

102

6.2

Luminosity Distance

106

6.3

Angular-diameter Distance

110

6.4

Standard Candles and H0

114

6.5

Standard Candles and Acceleration

116

Exercises

121

7 Dark Matter

123

7.1

Visible Matter

123

7.2

Dark Matter in Galaxies

128

7.3

Dark Matter in Clusters

130

7.4

Gravitational Lensing

135

7.5

What’s the Matter?

139

Exercises

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140

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

Contents

8 The Cosmic Microwave Background

ix

142

8.1

Observing the CMB

143

8.2

Recombination and Decoupling

147

8.3

The Physics of Recombination

150

8.4

Temperature Fluctuations

157

8.5

What Causes the Fluctuations?

159

Exercises 9 Nucleosynthesis and the Early Universe

164 166

9.1

Nuclear Physics and Cosmology

167

9.2

Neutrons and Protons

169

9.3

Deuterium Synthesis

174

9.4

Beyond Deuterium

177

9.5

Baryon–Antibaryon Asymmetry

181

Exercises 10 Inflation and the Very Early Universe

183 185

10.1 The Flatness Problem

186

10.2 The Horizon Problem

187

10.3 The Monopole Problem

189

10.4 The Inflation Solution

192

10.5 The Physics of Inflation

197

Exercises

202

11 Structure Formation: Gravitational Instability

204

11.1 The Matthew Effect

206

11.2 The Jeans Length

209

11.3 Instability in an Expanding Universe

213

11.4 The Power Spectrum

217

11.5 Hot versus Cold

221

11.6 Baryon Acoustic Oscillations

226

Exercises

230

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Contents

12 Structure Formation: Baryons and Photons

232

12.1 Baryonic Matter Today

233

12.2 Reionization of Hydrogen

235

12.3 The First Stars and Quasars

238

12.4 Making Galaxies

242

12.5 Making Stars

248

Exercises

254

Epilogue Table of Useful Constants Index

256 258 259

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Cambridge University Press 978-1-107-15483-4 — Introduction to Cosmology Barbara Ryden Frontmatter More Information

Preface

The first edition of this book was based on my lecture notes for an upper-level undergraduate cosmology course at The Ohio State University. The students taking the course were primarily juniors and seniors majoring in physics and astronomy. In my lectures, I assumed that my students, having triumphantly survived freshman and sophomore physics, had a basic understanding of electrodynamics, statistical mechanics, classical dynamics, and quantum physics. As far as mathematics was concerned, I assumed that, like modern major-generals, they were very good at integral and differential calculus. Readers of this book are assumed to have a similar background in physics and mathematics. In particular, no prior knowledge of general relativity is assumed; the (relatively) small amounts of general relativity needed to understand basic cosmology are introduced as needed. The second edition that you are reading now is updated with observational and theoretical developments during the 14 years that have elapsed since the first edition. It has been improved by many comments by readers. (My thanks go to the eagle-eyed readers who caught the typographical errors that snuck into the first edition.) The second edition also contains an extended discussion of structure formation in the final two chapters. For a brief course on cosmology, the first ten chapters can stand on their own. Unfortunately, the National Bureau of Standards has not gotten around to establishing a standard notation for cosmological equations. It seems that every cosmology book has its own notation; this book is no exception. My main motivation was to make the notation as clear as possible for the cosmological novice. Many of the illustrations in this book were adapted from figures in published scientific papers; my thanks go to the authors of those papers for granting permission to use their figures or to replot their hard-won data. Particular thanks go to Avishai Dekel (Figure 2.2), Wendy Freedman (Figure 2.5), David Leisawitz (Figure 8.1), Alain Coc (Figure 9.4), Richard Cyburt (Figure 9.5), Rien van de Weygaert (Figure 11.1), Ashley Ross (Figure 11.6), Xiaohui Fan (Figure 12.3),

xi

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xii

Preface

and John Beacom (Figure 12.4). Extra thanks are due to Anˇze Slosar and Jos´e Alberto V´azquez for their assistance with Figures 6.6, 8.7, and 11.7. Many people (too many to name individually) helped in the making of this book. I owe particular thanks to the students who took my undergraduate cosmology course at Ohio State University. Their feedback, including nonverbal feedback such as frowns and snores during lectures, greatly improved the lecture notes on which the first edition was based. The students of the graduate cosmology course at Ohio State have assisted in the development of the second edition, by field-testing the end-of-chapter problems, proposing new problems, and acting as all-around critics of the manuscript. Adam Black and Nancy Gee, at Pearson Addison Wesley, made possible the great leap from rough lecture notes to polished book. Vince Higgs and Rachel Cox, at Cambridge University Press, helped with the second great leap to a new, improved second edition. The reviewers of the text, in both its first and second editions, pointed out many omissions and suggested many improvements. The first edition of this book was dedicated to Rick Pogge, who acted as my computer maven, graphics guru, personal chef, and general sanity check. Obviously, there was only one thing to do with such a paragon. Reader, I married him.

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