Origins: Fourteen Billion Years Of Cosmic Evolution

Also by Neil deGrasse TysonThe Sky Is Not the Limit: Adventures of an Urban AstrophysicistCosmic Horizons: Astronomy at the Cutting Edge(with Steven Soter, eds.)One Universe: At Home in the Cosmos (with Charles Liu and Robert Irion)Universe Down to EarthJust Visiting This PlanetMerlin’s Tour of the UniverseAlso by Donald GoldsmithChaos to Cosmos: A Space Odyssey(with Laura Danly and Leonard David)Connecting with the Cosmos: Nine Ways to Experience the Wonder of the UniverseThe Search for Life in the Universe (with Tobias Owen; 3rd ed.)The Runaway Universe: The Race to Findthe Future of the CosmosThe Ultimate Planets BookWorlds Unnumbered: The Search for Extrasolar PlanetsThe Ultimate Einstein (with Robert Libbon)Einstein’s Greatest Blunder? The Cosmological Constant andOther Fudge Factors in the Physics of the Universe

Fourteen Billion Years ofCosmic EvolutionNeil deGrasse TysonandDonald GoldsmithW. W. NORTON & COMPANYNEW YORK LONDON

To all those who look up,And to all those who do not yet knowwhy they should

ContentsAcknowledgmentsPREFACEA Meditation on the Origins of Science and the Science of OriginsOVERTUREThe Greatest Story Ever ToldPart I: The Origin of the UniverseCHAPTER 1CHAPTER 2CHAPTER 3CHAPTER 4CHAPTER 5CHAPTER 6In the BeginningAntimatter MattersLet There Be LightLet There Be DarkLet There Be More DarkOne Universe or Many?Part II: The Origin of Galaxies and Cosmic StructureCHAPTER 7CHAPTER 8Discovering GalaxiesThe Origin of StructurePart III: The Origin of StarsCHAPTER 9CHAPTER 10Dust to DustThe Elemental ZooPart IV: The Origin of PlanetsCHAPTER 11CHAPTER 12CHAPTER 13When Worlds Were YoungBetween the PlanetsWorlds Unnumbered: Planets Beyond the Solar SystemPart V: The Origin of LifeCHAPTER 14CHAPTER 15CHAPTER 16Life in the UniverseThe Origin of Life on EarthSearching for Life in the Solar System

CHAPTER 17CODASearching for Life in the Milky Way GalaxyThe Search for Ourselves in the CosmosGlossary of Selected TermsFurther ReadingImage CreditsIndexPhoto Insert

AcknowledgmentsFor reading and rereading the manuscript, ensuring that we mean what we say and say what we mean,we are indebted to Robert Lupton of Princeton University. His tandem expertise in astrophysics andthe English language allowed the book to reach several notches higher than we had otherwiseimagined for it. We are also grateful to Sean Carroll at Chicago’s Fermi Institute, Tobias Owen of theUniversity of Hawaii, Steven Soter of the American Museum of Natural History, Larry Squire of UCSan Diego, Michael Strauss of Princeton University, and PBS NOVA producer Tom Levenson for keysuggestions that improved several parts of the book.For expressing confidence in the project from the beginning, we thank Betsy Lerner of the GernertAgency, who saw our manuscript not only as a book but also as an expression of deep interest in thecosmos, deserving the broadest possible audience with whom to share the love.Major portions of Part II and scattered portions of Parts I and III first appeared as essays in NaturalHistory magazine by NDT. For this, he is grateful to Peter Brown, the magazine’s editor in chief, andespecially to Avis Lang, their senior editor, who continues to work heroically as a learned literaryshepherd to NDT’s writing efforts.The authors further recognize support from the Sloan Foundation in the writing and preparation ofthis book. We continue to admire their legacy of support for projects such as this.Neil deGrasse Tyson, New York CityDonald Goldsmith, Berkeley, CaliforniaJune 2004

PREFACEA Meditation on the Origins of Science and theScience of OriginsA new synthesis of scientific knowledge has emerged and continues to flourish. In recent years, theanswers to questions about our cosmic origins have not come solely from the domain of astrophysics.Working under the umbrella of emergent fields with names such as astrochemistry, astrobiology, andastro-particle physics, astrophysicists have recognized that they can benefit greatly from thecollaborative infusion of other sciences. To invoke multiple branches of science when answering thequestion, Where did we come from? empowers investigators with a previously unimagined breadthand depth of insight into how the universe works.In Origins: Fourteen Billion Years of Cosmic Evolution, we introduce the reader to this newsynthesis of knowledge, which allows us to address not only the origin of the universe but also theorigin of the largest structures that matter has formed, the origin of the stars that light the cosmos, theorigin of planets that offer the likeliest sites for life, and the origin of life itself on one or more ofthose planets.Humans remain fascinated with the topic of origins for many reasons, both logical and emotional.We can hardly comprehend the essence of anything without knowing where it came from. And of allthe stories that we hear, those that recount our own origins engender the deepest resonance within us.Self-centeredness bred into our bones by our evolution and experience on Earth has led us naturallyto focus on local events and phenomena in the retelling of most origin stories. However, everyadvance in our knowledge of the cosmos has revealed that we live on a cosmic speck of dust, orbitinga mediocre star in the far suburbs of a common sort of galaxy, among a hundred billion galaxies in theuniverse. The news of our cosmic unimportance triggers impressive defense mechanisms in the humanpsyche. Many of us unwittingly resemble the man in the cartoon who gazes at the starry heavens andremarks to his companion, “When I look at all those stars, I’m struck by how insignificant they are.”Throughout history, different cultures have produced creation myths that explain our origins as theresult of cosmic forces shaping our destiny. These histories have helped us to ward off feelings ofinsignificance. Although origin stories typically begin with the big picture, they get down to Earthwith impressive speed, zipping past the creation of the universe, of all its contents, and of life onEarth, to arrive at long explanations of myriad details of human history and its social conflicts, as ifwe somehow formed the center of creation.Almost all the disparate answers to the quest of origins accept as their underlying premise that thecosmos behaves in accordance with general rules, which reveal themselves, at least in principle, toour careful examination of the world around us. Ancient Greek philosophers raised this premise toexalted heights, insisting that we humans possess the power to perceive how nature operates, as wellas the underlying reality beneath what we observe: the fundamental truths that govern all else. Quite

understandably, they insisted that uncovering those truths would be difficult. Twenty-three hundredyears ago, in his most famous reflection on our ignorance, the Greek philosopher Plato comparedthose who strive for knowledge to prisoners chained in a cave, unable to see objects behind them, andwho must attempt to deduce from the shadows of these objects an accurate description of reality.With this simile, Plato not only summarized humanity’s attempts to understand the cosmos but alsoemphasized that we have a natural tendency to believe that mysterious, dimly sensed entities governthe universe, privy to knowledge that we can, at best, glimpse only in part. From Plato to Buddha,from Moses to Mohammed, from a hypothesized cosmic creator to modern films about “the matrix,”humans in every culture have concluded that higher powers rule the cosmos, gifted with anunderstanding of the gulf between reality and superficial appearance.Half a millennium ago, a new approach toward understanding nature slowly took hold. This attitude,which we now call science, arose from the confluence of new technologies and the discoveries thatthey fostered. The spread of printed books across Europe, together with simultaneous improvementsin travel by road and water, allowed individuals to communicate more quickly and effectively, so thatthey could learn what others had to say and could respond far more rapidly than in the past. Duringthe sixteenth and seventeenth centuries, this hastened back-and-forth disputation and led to a new wayof acquiring knowledge, based on the principle that the most effective means of understanding thecosmos relies on careful observations, coupled with attempts to specify broad and basic principlesthat explain a set of these observations.One more concept gave birth to science. Science depends on organized skepticism, that is, oncontinual, methodical doubting. Few of us doubt our own conclusions, so science embraces itsskeptical approach by rewarding those who doubt someone else’s. We may rightly call this approachunnatural; not so much because it calls for mistrusting someone else’s thoughts, but because scienceencourages and rewards those who can demonstrate that another scientist’s conclusions are just plainwrong. To other scientists, the scientist who corrects a colleague’s error, or cites good reasons forseriously doubting his or her conclusions, performs a noble deed, like a Zen master who boxes theears of a novice straying from the meditative path, although scientists correct one another more asequals than as master and student. By rewarding a scientist who spots another’s errors—a task thathuman nature makes much easier than discerning one’s own mistakes—scientists as a group havecreated an inborn system of self-correction. Scientists have collectively created our most efficientand effective tool for analyzing nature, because they seek to disprove other scientists’ theories even asthey support their earnest attempts to advance human knowledge. Science thus amounts to a collectivepursuit, but a mutual admiration society it is not, nor was meant to be.Like all attempts at human progress, the scientific approach works better in theory than in practice.Not all scientists doubt one another as effectively as they should. The need to impress scientists whooccupy powerful positions, and who are sometimes swayed by factors that lie beyond their consciousknowledge, can interfere with science’s self-correcting ability. In the long run, however, errors cannotendure, because other scientists will discover them and promote their own careers by trumpeting thenews. Those conclusions that do survive the attacks of other scientists will eventually achieve thestatus of scientific “laws,” accepted as valid descriptions of reality, even though scientists understandthat each of these laws may some day find itself to be only part of a larger, deeper truth.