Solving Fermi’s Paradox

432 Pages·2019·11.691 MB·English

by  Duncan H. Forgan

SOLVING FERMI’S PARADOX
The Search for Extraterrestrial Intelligence (SETI) has for 60 years attempted to
solveFermi’sparadox:ifintelligentlifeisrelativelycommonintheuniverse,where
is everybody? Examining SETI through this lens, this volume summarises cur-
rent thinking on the prevalence of intelligent life in the universe and discusses 66
distinct solutions to the so-called paradox. It describes the methodology of SETI
and how many disciplines feed into the debate, from physics and biology, to phi-
losophy and anthropology. The presented solutions are organised into three key
groups: rare-Earth solutions, suggesting that planetary habitability, life and intel-
ligence are uncommon; catastrophist solutions, arguing that civilisations do not
survivelongenoughtomakecontact;andnon-empiricalsolutions,whichtakethe-
oretical approaches, such as that our methodology is flawed. This comprehensive
introductiontoSETIconcludesbylookingatthefutureofthefieldandspeculating
onhumanity’spotentialfate.
DUNCAN H. FORGAN is Associate Lecturer at the Centre for Exoplanet Sci-
ence at the University of St Andrews. He is a founding member of the UK SETI
researchnetworkandleadsUKresearcheffortsintotheSearchforExtraterrestrial
Intelligence. His work includes simulations of civilisation evolution, developing
observablesofintelligenceandpolicyforpost-detectionscenarios.

CAMBRIDGE ASTROBIOLOGY
SeriesEditors
BruceJakosky,AlanBoss,FrancesWestall,DanielPrieur,andCharlesCockell
BooksintheSeries:
1. PlanetFormation:Theory,Observations,andExperiments
EditedbyHubertKlahrandWolfgangBrandner
ISBN978-0-521-18074-0
2. FitnessoftheCosmosforLife:BiochemistryandFine-Tuning
EditedbyJohnD.Barrow,SimonConwayMorris,StephenJ.Freeland,and
CharlesL.Harper,Jr.
ISBN978-0-521-87102-0
3. PlanetarySystemsandtheOriginofLife
EditedbyRalphPudritz,PaulHiggs,andJonathanStone
ISBN978-0-521-87548-6
4. ExploringtheOrigin,Extent,andFutureofLife:Philosophical,Ethical,and
TheologicalPerspectives
EditedbyConstanceM.Bertka
ISBN978-0-521-86363-6
5. LifeinAntarcticDesertsandOtherColdDryEnvironments
EditedbyPeterT.Doran,W.BerryLyons,andDianeM.McKnight
ISBN978-0521-88919-3
6. OriginsandEvolutionofLife:AnAstrobiologicalPerspective
EditedbyMurielGargaud,PurificaciónLopez-Garcia,andHervéMartin
ISBN9780521-76131-4
7. TheAstrobiogicalLandscape:PhilosophicalFoundationsoftheStudyofCosmicLife
MilanM.C´irkovic´
ISBN9780521-19775-5
8. TheDrakeEquation:EstimatingthePrevalenceofExtraterrestrialLifethrough
theAges
EditedbyDouglasA.VakochandMatthewF.Dowd
ISBN978-1-107-07365-4
9. Astrobiology,Discovery,andSocietalImpact
StevenJ.Dick
ISBN978-1-108-42676-3
10. SolvingFermi’sParadox
DuncanH.Forgan
ISBN978-1-107-16365-2

SOLVING FERMI’S PARADOX
DUNCAN H. FORGAN
Universityof StAndrews,Scotland
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Identifiers:LCCN2018052247|ISBN9781107163652(alk.paper)
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Contents
Preface pagexvii
PartI Introduction 1
1 IntroducingtheParadox 3
1.1 FermiandHisParadox 3
1.1.1 TheParadox,inBrief 3
1.1.2 Fermi’sParadoxIsNotHis,andItIsn’taParadox 4
1.2 DrakeandHisEquation 7
1.3 TheGreatFilter 11
2 FactA–TheGreatSilence 15
2.1 RadioSETI 21
2.1.1 TheWaterHole 21
2.1.2 DopplerDrift 24
2.1.3 RadioFrequencyInterference 24
2.1.4 Single-DishRadioAstronomy 25
2.1.5 Multi-DishRadioInterferometry 27
2.1.6 AHistoryofRadioSETIobservations 30
2.2 OpticalSETI 30
2.2.1 ArtefactSETI 35
2.2.2 AHistoryofOpticalSETIObservations 37
3 ClassifyingScenariosandSolutionstotheParadox 38
3.1 ContactScenariosandtheRioScale 38
3.2 TheThreeClassesofCivilisation–theKardashevScale 40
3.3 TheThreeClassesofSolutionstoFermi’sParadox 43
3.3.1 RareEarth(R)Solutions 43
3.3.2 Uncommunicative(U)Solutions 44
ix
x Contents
3.3.3 Catastrophic(C)Solutions 44
3.3.4 HardandSoftSolutions 44
PartII RareEarthSolutions 45
4 HabitableWorldsAreRare 47
4.1 WorldsAreNotRare 47
4.1.1 TheFirstExoplanets–PulsarTiming 47
4.1.2 TheRadialVelocityMethod 48
4.1.3 TransitDetection 53
4.1.4 GravitationalMicrolensing 56
4.1.5 DirectImaging 61
4.1.6 DetectingLifeonExoplanets 64
4.1.7 TheExoplanetPopulation 68
4.2 HabitableZones 71
4.2.1 CircumstellarHabitableZones 71
4.2.2 GalacticHabitableZones 75
4.3 TheEarthasaHabitablePlanet 84
4.4 GoodandBadPlanetaryNeighbours 87
4.4.1 MilankovitchCycles 87
4.4.2 PlanetaryNeighboursasAsteroidShields 89
4.5 DoestheEarthNeedtheMoonToBeHabitable? 91
4.5.1 What Influence Does the Moon Have on Earth’s
Habitability? 91
4.5.2 WhatIftheMoonNeverExisted? 93
4.5.3 Are Large Moons Common in Terrestrial Planet
Formation? 95
5 LifeIsRare 98
5.1 WhatIsLife? 98
5.2 TheOriginsofLife 100
5.2.1 Oparin-HaldaneTheoryandtheMiller-Urey
Experiments 101
5.2.2 ‘Vents’Theories 103
5.2.3 ‘Pools’Theories 104
5.2.4 MultipleOriginsofLife? 104
5.3 TheMajorEvolutionaryTransitionsinTerrestrialOrganisms 104
5.3.1 Free-Floating Self-Replicating Molecules to
MoleculesinCompartments 105
5.3.2 IndependentReplicatorstoChromosomes 105