The new cosmic onion: quarks and the nature of the universe

233 Pages·2007·2.331 MB·English

by  Close, Frank

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Frank Close
University of Oxford,
England
New York London
Taylor & Francis is an imprint of the
Taylor & Francis Group, an informa business
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electron
atom
nucleus
proton
neutron
quark
Typical sizes: 1/100,000,000 cm 1/1,000,000,000,000 cm 1/10,000,000,000,000 cm
1/100,000,000,000,000 cm (or less)
Theseminutedistancescanbemoreeasilywrittenas10−8 cmforatoms,10−12 cmfor
nucleus, and 10−13 cm for a nuclear particle. Electrons and quarks are the varieties of
matterthatexistasdistancesoflessthan10−14cm.Thesearetheshortestdistancesthat
presenttechnologycanprobe.(Source:CERN.)
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Foreword
Whyarescientistsspending$10billiontobuildtheLargeHadronCollider(LHC)?
This question is being increasingly asked as this most ambitious project in particle
physicspreparesforitsgrandopeningin2007.Inanattempttoprovidesomeofthe
answersforapublicwhoknowofsciencebutwhoarenotnecessarilyprofessional
scientists,IdecidedtoproducethisnewversionofTheCosmicOnion.
The original version first appeared in 1983: a time when popular accounts of
particle physics were almost non-existent. Its title became a brand in its own right,
being widely adopted as a metaphor for the structure of matter consisting of ever
deeperlayers:fromgalaxiesofstars,toatoms,andthebasicseeds—quarks.Today,
by contrast, there is a vast literature on popular physics, increasingly focussed on
excitingbuthighlyspeculativeideassuchassuperstringtheory,higherdimensions,
andparalleluniverses.Sometimesitisdifficultforthepublictodistinguishbetween
whatissciencefactandsciencefictionor,inthewordsofBillBryson,1“legitimately
weird or outright crackpot; twaddle, a work of genius or a hoax.” I restricted the
originalCosmicOniontoestablishedconceptsthat,whiletheyoncemighthavebeen
classifiedasweirdgenius,hadmaturedtoestablishedconservatismthatIfeltwould
last:aquarterofacenturylater,Iampleasedtosaythatthishasturnedouttobethe
case.Butinthatperiodanumberofthingshavehappenedthathavealertedmetothe
passageoftimeandtheneedforTheNewCosmicOnion.
First, there was the personal shock when, about 10 years ago, undergraduates
startedtellingmethatTheCosmicOnionhadbeentheirfirstchildhoodintroduction
to the fascinating subject of particle physics. In the past 5 years, these childhood
experienceswerebeingrecalledbypost-doctoralresearchfellows;andwhenatenured
physicisttoldmeasmuch,Ifeltitwastimetostartwritingbeforeitwastoolate.On
thescientificfront,newdiscoverieshaveradicallychangedourperceptionofmatter
andtheuniverse,manyofwhichwereundreamedofin1983.Theseallhighlighted
howmanyyearshadpassedsinceIwrotetheoriginal:astheworldofparticlephysics
preparedfortheLHC,IdecideditwashightimetobringTheCosmicOnionupto
date.
Originallywrittenasapopulardescriptionofthenatureofmatterandtheforces
thatcontroltheuniverse,itgainedamuchwiderfollowing.Itwasusedasarecom-
mended background book in universities and schools; Sir John Kendrew’s national
committeereviewingBritain’sroleinworldhigh-energyphysicsandatleastoneU.K.
governmentministerofscienceuseditasabrief;itledtotheauthor’stelevisedRoyal
InstitutionChristmasLectures“TheCosmicOnion”in1993,aswellasinspiringa
generationofstudentstotakeupscience.
Byfocusingonconceptsthatwereinmyopinionestablished,Iampleasedthat
almostnothingofthatoriginalCosmicOnionhasprovedtobesohighlyconjectural
thatithasbeenoverthrown.Manynewfactshavecometobeknown,includingseveral
1Bryon,B.,AShortHistoryofNearlyEverything,BroadwayBooks,2003.
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thatwerenotanticipated,andmuchofthematerialinthelatterpartofthisnewversion
bearstestimonytothat.
Discoveriesandprecisionmeasurementsduringthepast10yearshaveestablished
Electroweak Theory as a law of nature. The discovery of the top quark had been
expected,butitwasasurprisethatitturnedouttobesomassive,somethirtytimes
greater than its sibling, the bottom quark. A question for the future is whether this
makesthetopquarktheoddoneoutorwhetheritistheonly“normal”one,existingon
thescaleofelectroweaksymmetrybreaking,whilealltheotherfundamentalparticles
areanomalouslylight.Inanyevent,thetopquarkisutterlydifferentandwhentheLHC
enablesittobestudiedindetailforthefirsttime,furthersurprisescouldensue.The
bottomquarkturnedouttobesurprisinglystable,whichhasopenedanewwindowinto
themysteryoftheasymmetrybetweenmatterandantimatter.Wehavelookedintothe
heartoftheSunandevenasupernovabymeansofneutrinos;thesehaveshownthat
neutrinosarenotsimplymasslessparticlesthattravelatlightspeed,andinturnthis
is opening up new research lines that were not on the theorists’ agenda in 1983.
TenyearsofprecisiondatafromLEPatCERNinGenevahaverevealedthesubtle
quantummechanicalinfluencethattheHiggsfieldhasonthevacuumandestablished
thecriteriabywhichtheHiggsBosonmaybeproduced.Inthecosmologicalarena
wearenowcomingtotheopinionthattheuniverseis“flat,”withappreciabledark
matter(aboutwhichsomewerebeginningtospeculate20yearsago)andalsodark
energy(whichwasutterlyunexpected).Quarksandleptonshavebeenshowntobe
structurelessparticlestodistancesassmallas10−19 m,whichisassmallrelativeto
aprotonastheprotonistothedimensionsofahydrogenatom.
Whiletheseadvanceshavebeendeliveredbyexperiment,therewerealsotheoret-
icalconcepts,suchassuperstrings,thatin1983wereonlyjustabouttoemerge,and
whicharenowamajormathematicalresearcharea.Itispossiblethatthiswilleven-
tuallyprovetobethelong-soughtTheoryofEverything;andtoreadsomepopular
science,orwatchitontelevision,youmighthavetheimpressionthatitisestablished
lore.However,thereisatpresentnoclearevidencetoshowthatithasanythingtodo
withthephysicsthathasbeenrevealedbyexperiment.Timeandexperimentwilltell,
andthatisforthefuture.Forthepresent,thatiswhyTheNewCosmicOnioncomes
withnostringsattached.
The New Cosmic Onion contains the best from the original, thoroughly revised
andupdated,plusextensivenewmaterialthatexplainsthescientificchallengesatthe
startofthe21stcentury.Newacceleratorsarebeingbuiltthatwillshowhowtheseeds
ofmatterwerecreatedwhenouruniversewaslessthanabillionthofasecondold.
Thediscoveriesinthiscenturypromisetobenolessrevolutionarythaninthelast.
ThehopeisthatTheNewCosmicOnionwillprovidetheexplanationsthatstudents,
opinionformers,andintelligentcitizensneediftheyaretounderstandhowscience
hascometothisfrontier,andwherewethinkitisheadedintheimmediatefuture.As
intheoriginal,IhaveselectedthecontentthatIbelievewilllast,andhaveavoided
flightsoffancythatmightnotsurvivethetestoftime.
Iamgratefultothemanypeoplewho,havingreadtheoriginal,wrotetomewith
corrections, questions, and suggestions. In particular, I am grateful to my physics
studentsatExeterCollege,Oxford,whohavereadtheoriginalaspartoftheirsum-
mer studies and identified points that needed better explanations. Some readers’
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suggestions are mutually exclusive, so the new version will not be to everyone’s
taste. Nonetheless, I anticipate and welcome comments, in the hope that once the
discoveriesstarttoflowfromtheLHC,revisionswillbeabletotakesuchcomments
into account. However, one result of writing such books is that the author receives
countlessletterswithnewsofthewriter’sproofthatEinsteinwaswrong,orofthem
havingstumbledonsomecodeofnumbersthatexplainsthemassesoftheparticles
intermsofπ ore.Scienceadvancesbynovelideas,certainly,butitisessentialthat
theynotonlyfitknownfacts,butalsomakesometestableprediction.Itisexperiment
thatdecideswhatistrueorfalse;thatiswhatIhaveusedasaparadigmindeciding
whattoincludeinandwhattoomitfromthisbook.
I am grateful to my students for their penetrating questions, and to my long-
suffering family and friends who have been used as sounding boards for potential
answers.IamgratefultoAnneandStuartTaylorfortheelegantwritingdeskattheir
Norfolkcottage,andtotheNorfolkWildlifeTrustforprovidingsuchwell-situated
birdhidesthatenabledmywifetospendhourswatchingnaturethroughhertelescopes,
whileIpassedthetimewaitingfortheBittern(thatnevershoweditself)bywriting
aboutNatureasrevealedbytheultimatemicroscopes.
FrankClose
Oxford,2006
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Suggestions for Further Reading
Thisisnotintendedasacomprehensiveguide,butratherasameansofextendingor
deepeningyourreadingonparticlephysics.
For the experimental aspects of particle physics, together with many images of
facilities,detectors,andparticletrails,seeTheParticleOdyssey,FrankClose,Michael
Marten, and Christine Sutton (Oxford University Press, 2003) or its predecessor,
TheParticleExplosion.Abriefsummarysuitableforundergraduatebackgroundread-
ingisParticlePhysics—AVeryShortIntroduction,FrankClose(OxfordUniversity
Press,2004).
A detailed technical introduction, which is excellent for serious students, is
NuclearandParticlePhysics,W.S.C.Williams(OxfordUniversityPress,1994).
A classic review of modern ideas in theoretical particle physics is Dreams of
a Final Theory by Steven Weinberg (Pantheon, 1992; Vintage, 1993). Two Nobel
Laureateswhosharedinthecreationofthebirthofelectroweaktheoryhavewritten
semi-popular books on the subject: In Search of the Ultimate Building Blocks by
G.’tHooft(CambridgeUniversityPress,1996)andFactsandMysteriesinElementary
ParticlePhysicsbyM.Veltman(WorldScientific,2003).
Asymmetry and the ideas of spontaneous symmetry breaking that underpin the
HiggsmechanismaredescribedinLucifer’sLegacybyFrankClose(OxfordUniver-
sityPress,2000),andbyHenningGenzinNothingness(PerseusBooks,1999).
BrianGreene’sTheElegantUniverse,Superstrings,HiddenDimensionsandthe
Quest for Ultimate Reality (Jonathan Cape, 1999) and Gordon Kane’s The Particle
Garden:OurUniverseasUnderstoodbyParticlePhysicistswilltakeyoutotheideas
on superstrings and other more speculative areas that are not covered in The New
CosmicOnion.Foracontraryviewpointaboutstringtheory,whichisperhapsnearer
to the thesis of the present book, try Not Even Wrong by P. Woit (Jonathan Cape,
2006).
Ihave,asfaraspossible,triedtoavoidthemysteriesofquantummechanics.For
thosewhowantapopularandinformedintroduction,readTheNewQuantumUniverse
byTonyHeyandPatrickWalters(CambridgeUniversityPress,2003).Amoreformal
but accessible introduction to the basic concepts is Quantum Mechanics — A Very
Short Introduction, John Polkinghorne (Oxford University Press). A history of the
earlydaysofquantummechanics,andthebirthofparticlephysicsisInwardBound
byAbrahamPais(OxfordUniversityPress,1986).
AclassicnontechnicaldescriptionoftheaftermathoftheBigBangisTheFirst
ThreeMinutesbyStevenWeinberg(AndreDeutsch,1977;BasicBooks,1993).
For more on the history of quarks, read The Hunting of the Quark by Michael
Riordan(SimonandSchuster,1987)andforthequark-relatedworkofMurrayGell
Mann, Strange Beauty by G. Johnson (Vintage, 2000). For more general history of
20thcenturyparticlephysics,TheParticleCenturyisacollectionofarticleseditedby