Constructing Reality: Quantum Theory and Particle Physics

296 Pages·2011·2.949 MB·English

by  John Marburger

Constructing Reality
Questionsofthefundamentalnatureofmattercontinuetoinspireand
engageourimagination.However,theexcitingnewconceptsof
strings,supersymmetry,andexoticmatterbuildonideasthatarewell
knowntophysicistsbutmysteriousandpuzzlingtopeopleoutsideof
theseresearchfields.
Coveringkeyconceptualdevelopmentsfromthelastcentury,this
bookprovidesabackgroundtotheboldideasandchallengesfacedby
physiciststoday.QuantumtheoryandtheStandardModelofparticles
areexplainedwithminimalmathematics,andadvancedtopics,such
asgaugetheoryandquantumfieldtheory,areputintocontext.With
concise,lucidexplanations,thisbookisanessentialguidetotheworld
ofparticlephysics.
john marburger,III,isUniversityProfessorofPhysicsand
ElectricalEngineeringandVicePresidentforResearchatStonyBrook
University.Previoustothis,hehasbeenScienceAdvisortothe
PresidentoftheUnitedStatesandDirectoroftheOfficeofScienceand
TechnologyPolicy,DirectorofBrookhavenNationalLaboratory,and
PresidentofStonyBrookUniversity.Hisaccomplishmentsinscience
policyandadministrationhavebeenrecognizedbynumerousawards
andhonors.

Constructing Reality
Quantum Theory and
Particle Physics
john marburger, iii
StonyBrookUniversity
cambridge university press
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Singapore,SãoPaulo,Delhi,Tokyo,MexicoCity
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Informationonthistitle:www.cambridge.org/9781107004832
©J.Marburger2011
Thispublicationisincopyright.Subjecttostatutoryexception
andtotheprovisionsofrelevantcollectivelicensingagreements,
noreproductionofanypartmaytakeplacewithoutthewritten
permissionofCambridgeUniversityPress.
Firstpublished2011
PrintedintheUnitedKingdomattheUniversityPress,Cambridge
AcatalogrecordforthispublicationisavailablefromtheBritishLibrary
LibraryofCongressCataloginginPublicationdata
Marburger,JohnH.(JohnHarmen)
Constructingreality:quantumtheoryandparticlephysics/JohnH.Marburger.
p. cm.
Includesbibliographicalreferencesandindex.
ISBN978-1-107-00483-2(hardback)
1. Quantumtheory. 2. Particles(Nuclearphysics) I. Title.
QC174.12.M3568 2011
530.12–dc22
2011000398
ISBN978-1-107-00483-2Hardback
CambridgeUniversityPresshasnoresponsibilityforthepersistenceor
accuracyofURLsforexternalorthird-partyinternetwebsitesreferredto
inthispublication,anddoesnotguaranteethatanycontentonsuch
websitesis,orwillremain,accurateorappropriate.
Contents
1. Thenatureofthings 1
1.1 Naturedoesnotconformtoourexpectations 3
1.2 Explanationversusdescription 5
1.3 Physicistskeeptryingtoexplain
the“unexplained” 6
Notes 7
2. Matterandmotioninspaceandtime 11
2.1 BernhardRiemannspeculatesontheempiricalnature
ofgeometry 11
2.2 Theworkofphysics 13
2.3 Newton’sunvisualizabledescription
ofNature’saction 17
2.4 Maxwelladdsfieldstothelistofthingsthatare 19
2.5 Maxwell’simpact(1):theinvariantspeedoflight 21
2.6 Einsteinexposesprejudicesaboutspaceandtime 23
2.7 AdigressiononE=mc2 25
2.8 Minkowskistretchesanewcanvasforthedepiction
ofNature 27
2.9 Theevolvinguniverseasatapestryofworld-linesin
space-time 29
2.10 Einsteinsaysthelawsofmotionmustnotdependupon
ourselves 31
2.11 Anewwayofthinkingaboutthelawsofmotion 33
2.12 An“explanation”forgravity 34
2.13 Weyl’sattempttoexplainelectromagnetism 37
2.14 ReflectionsonRiemann’sideaofgeometry
asphysics 40
Notes 41
vi contents
3. Realitylargeandsmall 52
3.1 Digressiononthequalityofknowledgein
auniverseofatoms 52
3.2 Maxwell’simpact(2):themismatchbetweenparticles
andfields 56
3.3 Planckpostulatesarelationbetweenenergy
andfrequency 57
3.4 ThematterwaveofdeBroglieandSchrödinger 62
3.5 Meanwhile,backinCopenhagen... 63
3.6 MaxBorn’sstatisticalinterpretation 64
3.7 Thequantummicroscopicworld
view:Step1 67
3.8 Schrödinger’scat 70
3.9 Wavesversusparticles 74
3.10 Aboutwaves 75
3.11 The“uncertaintyprinciple” 79
3.12 Amplitudesandphases 82
3.13 Quantumphaseasanew“dimension”
ofNature,andWeyl’striumph 85
3.14 Electromagnetism“explained” 89
Notes 91
4. ThelanguageofNature 102
4.1 Mathematicalthings 102
4.2 Schrödinger’swaveasasetofvectorcomponents 108
4.3 Thequantumstatevectorisnotofthisworld 112
4.4 Anewperspectiveonuncertaintyandcomplementarity 114
4.5 MorestructureforSchrödinger’swave:
“Intrinsicspin” 117
4.6 Spinisnotenough 121
4.7 Thepositronintrudes 122
4.8 Anti-matter 124
Notes 126
contents vii
5. Moreisdifferent 132
5.1 Thequantummicroscopicworldview:Step2 132
5.2 Systemswithmultipleexcitations 133
5.3 Quantumfieldtheory 135
5.4 Guessingequationsofmotion 137
5.5 “Statistics” 139
5.6 Aboutdetectors 143
5.7 ThedisturbingargumentofEinstein,Podolsky,
andRosen(EPR) 144
5.8 Bell’sinequality 148
5.9 Theentangleduniverse 151
Notes 152
6. Themachineryofparticlediscovery 157
6.1 Maxwell’simpact(3):atomismundermined 158
6.2 Particlespectroscopy 161
6.3 Thebigmachines 163
6.4 Neutronsandneutrinos 165
6.5 Moreinternal“dimensions”?Isospin 166
6.6 Mesonsandtherangeofforces 169
6.7 Ifisospinwere“real” 171
6.8 Symmetries(1):conservationlaws 174
6.9 Symmetries(2):groups 177
6.10 Symmetries(3):grouprepresentations 181
6.11 Thegameofparticlediscovery 183
6.12 Unitarityandrenormalization 184
6.13 Spontaneoussymmetrybreaking 187
Notes 190
7. TheStandardModel 197
7.1 Leptons 200
7.2 Quarks 203
7.3 Forces 209
7.4 ElectromagnetismandQED 210
7.5 ThestrongforceandQCD 214
viii contents
7.6 Theweakforce(butnoQWD) 221
7.7 Electro-weakunification 224
7.8 Parityviolation 226
7.9 CPviolation 227
7.10 Theproblemofmass 229
7.11 Adigressiononsuperconductivity 229
7.12 TheHiggsmechanism 231
7.13 TheHiggsboson(s) 234
Notes 236
8. Theproliferationofmatter 248
8.1 Anabbreviatedhistoryofcreation 248
8.2 Nucleonsandnuclei 252
8.3 Theperiodictableofelements 255
Notes 259
Epilogue:Beneathreality 262
Appendix:Howquantummechanics
isused 266
Notes 273
References 275
Index 282
1
The nature of things
I wrote this book for my friends who are not physicists, but who are
curiousaboutthephysicalworldandwillingtoinvestsomeeffortto
understand it. I especially had in mind those who labor to make the
workofphysicspossible–technicalworkersinotherfields,teachers,
science-minded public officials – who read popular accounts but are
hungry for a “next step” that might give them a firmer grasp of this
puzzling material. Physics gives me great pleasure, more from its
beautythanfromitsusefulness,andIregretthatmyenjoymentshould
dependontheeffortofsomanyotherswhodonotshareit.HereIhave
tried to ease my sense of guilt by attempting to disclose in ordinary
languagewhatmodernphysicsreallyisabout.Manysimilaraccounts
exist.1 In this one, I attempt to demystify the deep ideas as much as
possible in a nonmathematical treatment. Some mathematical ideas
areinevitable,andtheseItrytoexplain.Physicshasenteredanexcit-
ing phase with talk of new dimensions, exotic matter, and mind-
boggling events of cosmic scale. These dramatic ideas rest on a solid
conceptualframework,aproductofthelastcenturythatisnowoldhat
for physicists but remains exotic and impenetrable to most others.
This framework, quantum theory and the Standard Model of matter,
is an intellectual achievement of the highest order and essential for
understanding what comes next. My intention here is to provide a
reference and a guide to this known but still regrettably unfamiliar
world.
Different physicists have different interests, but I think most
would agree that the evolution of our field during the twentieth
centurystirsdeepaestheticfeelings.Iwilltrytoexplainwhythisis
so, but cannot guarantee readers will have the same reaction. My
accountisnotcomplete,norfaithfultothecomplexhistoryofthese