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T H E F R O N T I E R S C O L L E C T I O N U L T I M A T E HH OO R I Z O N S U L T I M A T E H O R I Z OO NN SS U L T I M A T E H O R I Z O N S U L T II MM A Helmut Satz T E H O R I Z O N S U L T I M A T E H O R I Z O N S U L T I M A T E H O R I Z O N S U L T I M A T E H O R I U LT I M ATZ OEN S U L T I M A T E H O R I Z O N S U L T I M A T E H O R I Z O N S UU L T I M A T E H O R I Z O N S U L TT II MM A T E H O R I Z O N S U L T I M A T E H O R I Z O N S U L T I M A H O R I Z O N S T E H O R I Z O N S UU LL T I M A T E H O R I Z O N S U L T I M A T E H O RR I Z O N S U L T I M A T E H O R I ZZ OO N SS UU LL T I M A T E H O R I Z O N S UU LL TTT II MM AA TT EE HH OO R I Z O N S Probing the Limits of the Universe 123 THE FRONTIERS COLLECTION Series editors Avshalom C. Elitzur Université Grenoble I Centre Équation, Labo. Verimag, Gières, France e-mail: [email protected] Laura Mersini-Houghton Department of Physics & Astronomy, University of North Carolina, Chapel Hill, North Carolina, USA e-mail: [email protected] T. Padmanabhan Inter University Centre for Astronomy and Astrophysics (IUC), Pune University Campus, Pune, India e-mail: [email protected] Maximilian Schlosshauer Institute for Quantum Optics and Quantum Information Austrian Academy of Sciences, Portland, Oregon, USA e-mail: [email protected] Mark P. Silverman Department of Physics, Trinity College, Hartford, Connecticut, USA e-mail: [email protected] Jack A. Tuszynski Department of Physics, University of Alberta, Edmonton, Alberta, Canada e-mail: [email protected] Rüdiger Vaas University of Giessen, Giessen, Germany e-mail: [email protected] For furthervolumes: http://www.springer.com/series/5342 THE FRONTIERS COLLECTION Series Editors A. C. Elitzur L. Mersini-Houghton T. Padmanabhan M. Schlosshauer M. P. Silverman J. A. Tuszynski R. Vaas The books in this collection are devoted to challenging and open problems at the forefrontofmodernscience,includingrelatedphilosophicaldebates.Incontrastto typical research monographs, however, they strive to present their topics in a manner accessible also to scientifically literate non-specialists wishing to gain insightintothedeeperimplicationsandfascinatingquestionsinvolved.Takenasa whole,theseriesreflectstheneedforafundamentalandinterdisciplinaryapproach tomodernscience.Furthermore,itisintendedtoencourageactivescientistsinall areas toponderoverimportantandperhapscontroversialissuesbeyondtheirown speciality. Extending from quantum physics and relativity to entropy, conscious- ness and complex systems—the Frontiers Collection will inspire readers to push back the frontiers of their own knowledge. Helmut Satz ULTIMATE HORIZONS Probing the Limits of the Universe 123 Helmut Satz FakultätfürPhysik Universität Bielefeld Bielefeld Germany ThisworkappearsinaparallelGermanedition‘‘GottesunsichtbareWürfel’’,publishedby C. H.BeckVerlag. ISSN 1612-3018 ISSN 2197-6619 (electronic) ISBN 978-3-642-41656-9 ISBN 978-3-642-41657-6 (eBook) DOI 10.1007/978-3-642-41657-6 Springer Heidelberg NewYork Dordrecht London LibraryofCongressControlNumber:2013953242 (cid:2)Springer-VerlagBerlinHeidelberg2013 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpartof the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,broadcasting,reproductiononmicrofilmsorinanyotherphysicalway,andtransmissionor informationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodology now known or hereafter developed. Exempted from this legal reservation are brief excerpts in connection with reviews or scholarly analysis or material supplied specifically for the purposeofbeingenteredandexecutedonacomputersystem,forexclusiveusebythepurchaserofthe work. Duplication of this publication or parts thereof is permitted only under the provisions of theCopyright Law of the Publisher’s location, in its current version, and permission for use must always be obtained from Springer. Permissions for use may be obtained through RightsLink at the CopyrightClearanceCenter.ViolationsareliabletoprosecutionundertherespectiveCopyrightLaw. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexempt fromtherelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. While the advice and information in this book are believed to be true and accurate at the date of publication,neithertheauthorsnortheeditorsnorthepublishercanacceptanylegalresponsibilityfor anyerrorsoromissionsthatmaybemade.Thepublishermakesnowarranty,expressorimplied,with respecttothematerialcontainedherein. Printedonacid-freepaper SpringerispartofSpringerScience+BusinessMedia(www.springer.com) In memory of my mother who dared to venture into the unknown in search of a better life for her sons Preface Confronted with the choice between paradise and knowledge, man, according to theBible,chose knowledge.Werethesereallyalternatives?Itcame tobethatthe gainingofknowledgeandthewiderhorizonoutsidethegardenofEdenbroughtto many as much pleasure and satisfaction as any paradise they could imagine. Humans have always wanted to explore the world they live in, and they have always wanted to know what lies beyond the horizons that limit their view. The search for richer pastures, better climates, easier communication—all these cer- tainlyplayedapartinthis,butbehinditalltherewasaninherenthumansenseof curiosity. This curiosity triggered a journey starting some 200,000 years ago in a remotecornerofAfricaandhasdrivenustonavigatealltheoceans,toconquerthe entire Earth, to probe the heavens and to penetrate ever more deeply into inter- stellar space, to study ever more distant galaxies. At the other end of the scale, high-energy particle accelerators allow us to resolve the structure of matter to an everhigherdegree,tolookforitsultimateconstituentsandstudyhowtheyinteract witheachothertoformourworld.Aretherelimits,isthereanendtothisdrive,at the large scale as well as at the small? Inthelasthundredyears,modernphysicsandcosmologyhaveshownthatthere existregionsforeverbeyondourreach,hiddenfromusbytrulyultimatehorizons. Theseregions wecanaccessinourimaginationonly;wecanspeculatewhatthey arelikeandwhetherperhapssomesignoftheirexistence,someindicationoftheir nature can ever reach our world. Suchhiddenregionsexistinthoseremotepartsoftheuniversewhere,fromour point of view, space expands faster than the speed of light. Closer to us, they are foundinblackholes,wheregravityisstrongenoughtoretainevenlightwithinits horizon of ultimate attraction. And in the realm of the very small, quarks remain forever confined to their colorful world of extreme density; they can never be removed from it. But given the Big Bang origin of the universe, our world in its veryearlystageswasimmenselyhotanddense;andgiventhespectrumofallthe particles created in high-energy collisions, we can try to reconstruct ever earlier stages. The evolution of the universe, with cooling and expansion, then defines horizons in time, thresholds through which the universe had to pass to reach its present state. What were the earlier stages like? vii viii Preface Althoughitisnotpossibletotransmitinformationacrossthe‘‘eventhorizons’’ that form the borders of these forbidden regions, still sometimes strange signals may appear, providing us with hints of the existence of those other worlds. Such striking phenomena can become possible through quantum effects; ‘‘Hawking– Unruh’’ radiation provides one example expected to arise in a variety of cases, whenever there exists an event horizon. And looking at the multitude of ‘‘ele- mentary’’ particles produced in high-energy accelerators, we can speculate that they originally came from a simpler, more symmetric world, which in the course of the evolution experienced transitions, like the freezing of water or the mag- netization of metals, to form the many-faceted and less symmetric world we see today. Theaimofthisbookistotellthestoryofhowthedifferenthorizons,onEarth and in the heavens, on large and on small scales, now and in the past, were discoveredandusedtodefineourviewoftheworld.Itisastoryoftheevolutionof this view, which started before ‘‘science,’’ and which is much more than just ‘‘something for scientists.’’ It started with philosophers wondering what matter wasmadeof,andhow;withsailorsdaringtofindoutiftheworldendssomewhere; withastronomerstryingtodetermineourpositionamongthestars,toestimatethe size of the Earth by looking at the Sun and using the newly developed geometry. With Edgar Allan Poe, the Big Bang appeared in literature before it was com- monplace in physics and cosmology; and aspects of both black holes and worm- holes were part of the stories of Lewis Carroll before they became significantly appreciated in science. Many of the ideas, even today’s, have come up here and there inthe course oftime.Thewaysof treating them, andthe toolsused for that were different, ofcourse, and changed over the centuries. But what remained was thatdesiretoseewhatliesbeyond,andtofindoutwhetherthereisalimittowhat we can reach and understand. We begin by looking at the various horizons partitioning our world and then showhowdifferentforbiddenregionsariseintheuniverse,andwhenandhowthey canemitsignaturesastestimonytotheirpresenceandtheirnature.Themysterious light emerging fromaneventhorizon, orthe equally mysteriousclustersinanew andstrangeether,theymaywellremainallthatwecaneverseeofwhatishidden beyond the ultimate horizons. This book is not meant to give a systematic presentation of the recent devel- opments in physics or cosmology. Its aim is to tell a story that began a long time ago and that will certainly not come to an end very soon. And it covers devel- opmentsthatsometimes,asintheageofVascodaGamaandColumbus,orinthe time of Einstein, Planck, Bohr and Heisenberg, revolutionize the world in two or three decades. At other times, between Ptolemy and Copernicus, it takes a mil- lennium to add a couple of epicycles to the accepted scheme of things. The problem is, in the words of the renowned Austrian theorist Walter Thirring, that ‘‘to do something really new, you have to have a new idea,’’ and that does not happen so very often. It does not suffice to play on the keyboard of the available theoreticalformalisms;thisjustleadstomanymelodiesandnottoanyconvincing and lasting new harmony. Preface ix Ihavetriedtopresentthingsinawaynotneedinganymathematics.Thatis,asI indicate in the section on Notation, a two-sided issue. Even Einstein sometimes presentedthespecialtheoryofrelativityintermsofpeopleonatrainversuspeople on the ground. It can be done, and it is indeed helpful to convey the basic ideas. For a full understanding of the ultimate conclusions, however, mathematics becomesessential.Totravelamiddleroad,Ihaveattimesaddedinserts,inwhich someaspectsofthebasic mathematicalformulationareindicated. ButIhopethat the presentation remains understandable even if you skip these. One unavoidable aspect appears if one tries to present things in as readable a way as possible: some points and concepts are mentioned more than once. Although strictly speaking logical, the reminder ‘‘as already discussed in the previousChapter’’isinfactoftennotwhatthereaderwants;itseemsbettertojust briefly recall the idea again. So I offer my apologies for a number of repetitions. And another apology is probably also needed. When forced to choose between scientific rigor and simplifying an idea enough to make it understandable, I gen- erallytookthelatterpath.Ithoughtitbettertotrytohavereadersfollowmytrain of thought, even if they will later need corrections, than to lose them in technical detailstheycannotfollow.MyinspirationherewerethewordsofthegreatDanish physicist Niels Bohr, who noted that Wahrheit (truth) and Klarheit (clarity) are complementary: the more precisely you enforce one, the less precise the other becomes. Finally, it is my pleasure to express sincere thanks to all who have helped me withthisendeavor.ObvioussupportcamefrommycolleagueshereinBielefeld,in Brookhaven, at CERN, in Dubna and elsewhere. They have been of crucial importance in forming my view of things. And last, but far from least, profound thanks go to my wife, who has patiently borne with me during all these years. Bielefeld, May 2013 Helmut Satz Contents 1 Horizons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 The Horizon of Accessibility . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Forbidden Rooms in the Universe . . . . . . . . . . . . . . . . . . . . . . 6 1.3 Ultimate Constituents. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4 The End of the Earth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.5 The Roof of Heaven . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2 The Vanishing Stars. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.1 The Speed of Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.2 Why Is the Sky Dark at Night?. . . . . . . . . . . . . . . . . . . . . . . . 29 2.3 The Big Bang. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.4 Cosmic Inflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.5 The Absolute Elsewhere. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 3 The Secret Glow of Black Holes. . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1 The Escape Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.2 Tidal Effects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.3 The Sea of Unborn Particles. . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.4 Invisible Light on the Horizon . . . . . . . . . . . . . . . . . . . . . . . . 54 4 The Visions of an Accelerating Observer . . . . . . . . . . . . . . . . . . . 59 4.1 Gravity and Acceleration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 4.2 A Total End of Communication . . . . . . . . . . . . . . . . . . . . . . . 63 4.3 The Temperature of the Vacuum. . . . . . . . . . . . . . . . . . . . . . . 64 4.4 Lightning in Empty Space . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.5 Quantum Entanglement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 5 The Smallest Possible Thing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 5.1 Why Does the Sun Shine? . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 5.2 The Strong Nuclear Interaction. . . . . . . . . . . . . . . . . . . . . . . . 78 5.3 The Weak Nuclear Interaction. . . . . . . . . . . . . . . . . . . . . . . . . 84 5.4 The Quarks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 5.5 The Standard Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.6 The Confinement Horizon . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 xi