by George Rhee
George RheeAstronomers' UniverseCosmic Dawn2013The Search for the First Stars and Galaxies10.1007/978-1-4614-7813-3© Springer Science+Business Media, LLC 2013
Astronomers' Universe
For further volumes: http://www.springer.com/series/6960
George Rhee
Cosmic Dawn
The Search for the First Stars and Galaxies
George RheeDepartment of Physics & Astronomy, University of Nevada, Las Vegas, Nevada, USA
ISSN 1614-659X
ISBN 978-1-4614-7812-6e-ISBN 978-1-4614-7813-3
Springer New York Heidelberg Dordrecht London
Library of Congress Control Number: 2013940914
© Springer Science+Business Media, LLC 2013
Cover image credits: Simulation: Matthew Turk, Tom Abel & Brian O’Shea Visualization: Ralf Kaehler and Tom Abel (KIPAC/Stanford)
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To Heidie, to the memory of Albert and Helen Rhee
Preface
Ulysses is telling Dante about his final fatal voyage, beyond the Pillars of Hercules, beyond the borders of the known world. Thanks to this episode in Dante’s poem, Ulysses has become one of the worlds great symbols of human dignity and human resource, a representative of the human compulsion to follow knowledge …Ulysses goes on to tell Dante of the courage that was required to initiate and pursue his adventure; I set forth then upon the open sea with just one vessel from my fleet’s remains and those few men who had not deserted me.
Seamus Heney, Speech delivered to the Human Rights Organization Frontline January 2002
When I was a boy I attended lectures by Rafel Carreras at the European Center for Nuclear Research (CERN) in Geneva Switzerland. These weekly popular science lectures were attended by people from all walks of life. As Carreras puts it
I often had university professors in the audience, schoolchildren, pensioners, sometimes even a mother feeding her baby, not forgetting the former CERN staff member whose job in my early years had been to clean off the blackboards at the end of my lectures, who, after he had retired, used to attend my lectures and sit in the front row
Carreras’ job description at CERN was to “contribute to the intellectual health of the staff”. Maybe every organization should have such a position. I hope this book will fill the reader with enthusiasm and encourage them to further explore the wonderful field of astronomy. It is in the Carreras spirit of sharing knowledge that I have written this book.
The book is aimed at the general public. It is not intended to be a textbook but rather an accessible overview of cosmology. The purpose of this book is to guide the reader to one of the frontiers of the field; the search for the first galaxies that formed after the big bang.
I feel I have two main duties as an author in writing a book such as this. Firstly, the book should not be boring, and secondly, it should provide correct scientific information. I hope I have achieved the goal of being entertaining without compromising accuracy.
Progress in cosmology is driven on the one hand by creative thinking and on the other by vast improvements in computing, telescope and instrument design. We stand on the brink of uncharted territory to be explored with the next generation of telescopes. It is easy for astronomers to impress the public with the awe inspiring images produced by telescopes such as the Hubble Space Telescope. I hope after reading this book, the reader will have the insight to appreciate the deeper significance of these images placed in their scientific context. For the most part I hope the reader will feel the same sense of wonder that I felt as a boy when I discovered science. Knowledge and wonder go hand in hand in the field of cosmology.
I would like to thank my colleagues at the University of Nevada, Stephen Lepp, Tao Pang, Bing Zhang, Daniel Proga and Ken Nagamine for providing a stimulating intellectual environment in which to think and write about these problems. Colleagues at other institutions including Rien van de Weygaert, Anatoly Klypin, Octavio Valenzuela and Fabio Governato have helped shape my ideas. I acknowledge support by the NSF AST-04-07072 grant to the University of Nevada, Las Vegas. I thank Doug Haag for his careful reading of the manuscript. I thank Heidie Grigg for her constant love and encouragement that made it possible for me to do this work. Let us then, like Ulysses, set forth on the open sea…
George Rhee
Las Vegas, NV, USA
De Guiche Monsieur, Have you read Don Quixote?
Cyrano Read it? I’ve practically lived it.
De Guiche I suggest you study the passage about the windmills.
Cyrano Chapter thirteen.
De Guiche When you make war on windmills you may find that the mill sails will swing their heavy spars and cast you down into the mud.
Cyrano Or up among the stars!
Edmond Rostand. Cyrano de Bergerac.
Abbreviations 1
ALMAAtacama Large Millimeter Array
CCDCharge Couple Device
CERNEuropean Center for nuclear Research
COBECosmic Background Explorer
ESOEuropean Southern Observatory
ESAEuropean Space Agency
E-ELTESO-Extremely Large Telescope
HSTHubble Space Telescope
NASANational Aeronautics and Space Administration
JWSTJames Webb Space Telescope
SDSSSloan Digital Sky Survey
SKASquare Kilometer Array
VLAVery Large Array
WMAPWilkinson Microwave Anisotropy Probe
Contents
Part I Prologue
1 Cosmology Through Its Past
2 The Three Pillars of the Big Bang Theory
3 The Visible Universe
4 Dark Matter
Part II The Emergence of Galaxies
5 A Map of the Universe
6 How Did Galaxies Come into Existence?
7 The Weight, Shape, and Fate of the Universe
Part III The Search for the Cosmic Dawn
8 The Search for Light in the Dark Ages
9 Observing the First Galaxies
&nb
sp; 10 Cosmic Archaeology
11 Looking Ahead in Wonder: Telescopes at the Cosmic Frontier
12 Tour de Force: The James Webb Telescope
Epilogue
Footnotes
1I have tried to avoid abbreviations as much as possible in this book, but a few have crept in that I list below.
Part 1
Prologue
George RheeAstronomers' UniverseCosmic Dawn2013The Search for the First Stars and Galaxies10.1007/978-1-4614-7813-3_1© Springer Science+Business Media, LLC 2013
1. Cosmology Through Its Past
George Rhee1
(1)Department of Physics & Astronomy, University of Nevada, Las Vegas, Nevada, USA
Abstract
One of the characters in the 1950s British comedy radio series, The Goon Show, once remarked that “Everybody’s got to be somewhere.” The answer to the question of where we are in the universe and how we got there has changed dramatically over the centuries. It is a question that all cultures try to answer in one way or another. We begin with a Native American myth and then discuss Greek thought and the idea of rational inquiry. The development of theories of planetary motion are discussed leading to the work of Isaac Newton. The implications of Newton’s theory for the idea of an infinite universe are presented. The telescope enters the stage, and we discuss its use in changing our view of the solar system. The discovery of nebulae by telescopic observations leads us to the story of how the nature of galaxies was revealed. We end with the discovery of the expanding universe and the idea of the Big Bang.
The Greeks were the first mathematicians who are still ‘real’ to us today…So Greek mathematics is permanent, more permanent even than Greek literature. Archimedes will be remembered when Aeschylus is forgotten because languages die and mathematical ideas do not.
G.H. Hardy, A Mathematician’s Apology
One of the characters in the 1950s British comedy radio series, The Goon Show, once remarked that “Everybody’s got to be somewhere.” The answer to the question of where we are in the universe and how we got there has changed dramatically over the past 2,000 years. It is a question that all cultures try to answer in one way or another. We discuss in this chapter the history of our attempts to answer this question. I begin with a Native American myth and then discuss Greek thought and the idea of rational inquiry. The ideas of motion in the solar system are discussed leading to the work of Isaac Newton. This, in turn, leads to thoughts on cosmology and the infinite universe. The telescope enters the stage, and we discuss its use in changing our view of the solar system and how galaxies was discovered. We close this chapter with the story of how the nature of galaxies was revealed and a description of work on cosmology in the first half of the twentieth century.
A Journey Back in Time: The Grand Canyon
The Grand Canyon of the Colorado River is one of the most spectacular places on earth. To journey into the Grand Canyon is to take a trip into the Earth’s past. At the deepest point the rocks one sees are over 2 billion years old, one-seventh of the age of the universe. One of many striking places in the Grand Canyon is the confluence of the Little Colorado River with the main Colorado River. Here, one can see a major part of the Earth’s history at a glance, from the 300-million-year-old rocks at the rim to the 2-billion-year-old rocks at the bottom. Near this place is a mound of earth that has great significance for the native Hopi people, who believe that the first people were created in a cave deep below the Earth’s surface. According to the Hopi myth, these first people climbed up through caves from lower worlds until they reached the earth’s surface and entered the fourth world through a hole in the earth known as the Sipapu. For the Hopi this is the holiest spot on earth. The Hopi people believe that the fourth world is sacred and that if the land is abused they will lose their sacred way of life.
This myth speaks to the human thirst for knowledge of origins. Our sense of identity is linked to our sense of history. Cosmology seeks to answer the same questions that myths address. How did things come to be the way they are today? Where do we come from? How did we get here? The history of cosmology reveals that our answers are determined by our view of the universe and include the limitations of that view. Our cosmology is determined by how much of the universe we can see with our eyes and our telescopes, and, for most of history, astronomy was done without telescopes.
We shall see that our current questions are more specific; What were the first objects to light up the universe and when did they do it? How do cosmic structures form and evolve? What are dark matter and dark energy?
Magic Reason and Experience: The Legacy of the Greek Thinkers
Our discussion of the origin of modern science begins with the works of ancient Greek thinkers. It is generally agreed that inquiries that are recognizable as science and philosophy were developed in the ancient world. Important developments took place from the sixth to the fourth centuries B.C. It is in this period that writers began to criticize what they called magical beliefs, and in particular criticized claims of the ability to forcibly manipulate the divine or supernatural. As an example, a treatise was written that exposed as frauds those who claimed to be able to cure epilepsy by purification, incantations, and other rituals.
The Greek idea of astronomy involved using a model to reproduce the observed motions of celestial objects in the night sky. Most Greek cosmologists placed the earth at the center of the universe. To our modern eyes, this seems perhaps egotistical. What is so important about our little planet that it should be at at the center of the universe? Greek scientists had actually searched for evidence of the Earth’s motion through space and found it lacking. Placing the earth at rest at the center was the simplest hypothesis consistent with the available facts.
Greek astronomers noticed that stars retain their positions relative to each other from night to night. The shape and relative positions of the constellations do not appear to change from one year to the next. This was true for all but five stars which appeared to move from one constellation to the next throughout the year. They called these objects planets, the Greek word for wanderers. The Greeks studied the motions of these planets relative to the stars and noticed that at certain times of the year a planet would stop its drift relative to the stars and change direction for a few weeks, then reverse its direction again, a phenomenon known as retrograde motion.
As we shall see, retrograde motion is really an optical illusion caused by the way the Earth passes other planets on its orbit around the Sun. Greek astronomy consisted of the study of the solar system, but their mathematical approach to the problem has enabled scientists to develop the big bang theory.
Mathematics, the Language of the Book of Nature
The Greek universe consisted of planets moving against a backdrop of fixed stars. The central issue for Greek cosmology was thus to explain planetary motion. The problem of planetary motion could have been solved in an easy way by invoking spirits. According to that view, the planets start their backwards motion during a certain month because they feel like it. It was not known at the time that planets are inanimate pieces of rock or gaseous spheres. When I walk down the street and suddenly stop, realizing I have not locked the house, I turn around of my own free will and go back and lock it, perhaps planets behave the same way. The Greeks had the deep insight to formulate a question that was to yield a fruitful answer. Might there not, they asked, be simple mathematical laws that govern motion of the planets? It turns out, remarkably, that the laws of physics can be written in mathematical form. Why this should be is a deep mystery. The world around us is remarkably complex. Weather patterns, the ebb and flow of life, human interactions, cannot be quantified by simple laws. Yet surprisingly, underlying all this complexity are simple laws that govern the behavior of all matter.
A hydrogen atom at the other end of our galaxy, 100,000 light years away will have exactly the same properties as a hydrogen atom in my body. This is a reflection of the fundamental laws of physics. The Greeks did no
t discover the fundamental laws of nature or even have the correct answers regarding motion in our solar system. Much more importantly however, they were asking the right questions. Science is the art of the soluble. The question the Greek astronomers posed was “is it possible to construct a simple mathematical model that explains the observed motions of the planets?” The model they constructed, much like our physical laws today, was an approximation, that provided a good fit to the best available measurements of the time.
The Greeks believed that the heavens embody perfection. The most perfect mathematical object known to them was a circle, so the Greeks constructed models based on uniform circular motion. The Greek model of the cosmos consisted of concentric spheres with the Earth at the center. To account for retrograde motion it was necessary to have at least two spheres for each planet. In practice a model for the solar system could consist of 20–50 spheres. For each planet a large sphere was necessary to account for the general drift of a planet and a smaller sphere was required to account for retrograde motion in the manner that we observe it. The model was described by Ptolemy (circ. AD 100–170) in a book called the Almagest which explained the motions of heavenly bodies and gave instructions as to how to calculate them. The Ptolemaic system agreed quite well with the observations available at the time and remained in use for the next 1,500 years. As I will explain in more detail below, astronomical observations made in the sixteenth and seventeenth centuries ultimately disproved the model.
