Cosmic Update: Dark Puzzles. Arrow of Time. Future History

151 Pages·2012·2.62 MB·English

by  Fred Adams

Cosmic Update
MultiversalJourneys
FoundingEditor: FarzadNekoogar,President
MultiversalJourneys
EditorialAdvisoryBoard: DavidFinkelstein,GeorgiaInstituteofTechnology
LawrenceM.Krauss,ArizonaStateUniversity
MarkTrodden,UniversityofPennsylvania
Forfurthervolumes:
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Fred Adams (cid:2) Thomas Buchert
Laura Mersini-Houghton
Farzad Nekoogar
Founding Editor
Cosmic Update
Dark Puzzles. Arrow of Time. Future History
123
FredAdams ThomasBuchert
DepartmentofPhysics Universite´Lyon1
RandallLaboratory CentredeRechercheAstrophysiquedeLyon
UniversityofMichigan CNRSUMR5574
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USA [email protected]
[email protected]
LauraMersini-Houghton
DepartmentofPhysicsandAstronomy
UniversityofNorthCarolina
ChapelHillNorthCarolina
USA
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FoundingEditor
FarzadNekoogar
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Preface
Outfornoreasonthisuniversecametobe
Outofaplacetobe,thisuniversefilleditself
Rumi
1207–1273
Many cultures throughout the history including the Greeks, ancient Egyptians,
Indians, Chinese, and Persians fascinated by the night sky studied stars and
the heavens for centuries. However, the study of the cosmos in the form of
classical scientific astronomy using mathematical descriptions is traced back to
early seventh century AD. From seventh to fourteenth century, Persian mathe-
maticians and astronomers Kharazmi (780–850), Biruni (973–1048), Khayyam
(1048–1131),Tusi(1201–1274),andKashani(1380–1429)eachcontributedalotto
thefieldofastronomy.Theircontributionswerefurtherdevelopedandimprovedby
EuropeanastronomersCopernicus(1473–1543),Galileo(1564–1642),andKepler
(1571–1630)overthenextthreecenturies.SirIsaacNewton’stheoryofgravitation
revolutionizedastronomicalcalculationsbylatesixteenthcentury(in1687,Newton
published his Principia). Newtonian mechanics made it possible to formulate the
motionofallcelestialbodiesinthesolarsystemandbeyond.
New discoveries and theories within the last century have drastically changed
our understanding of the cosmos. With the advent of Einstein’s General Theory
of Relativity and the observational discovery on the expansion of the Universe
by Slipher, as well as Hubble’s discovery of Hubble’s law (indicating that far
galaxies are receding from us) as early as 1920s, cosmology became a much
more distinct science than astronomy. In 1922, Alexander Friedmann’s solutions
to Einstein’s equations formulated the evolution of a relativistic expanding or
contracting dynamic Universe. The more advanced models are now known as
Friedmann–Lemaitre–Robertson–Walker (FLRW) models of cosmology due to
manyenhancementsandcontributionsfromothercosmologists.
From 1930s onward, the Big Bang theory formed the basis for explaining
the expansion of the Universe. However, the original Big Bang theory endured
three problems, namely, the smoothness problem, the horizon problem, and the
vii
viii Preface
flatness problem. The first problem asks why the matter is uniformly distributed
in the Universe. The second problem concerns the large-scale uniformity of the
observable Universe. Finally, the third problem asks why the Universe is close to
being spatially flat. With the introductionof the InflationaryModelof cosmology
in 1980s by Alan Guth, the three problems of the Big Bang cosmological model
weresolved.Accordingtoinflationarycosmology,thesizeoftheUniverseexpanded
exponentiallytoanextremelyhugenumber(1060/ofitsoriginalsize.Thishappened
inaveryshorttimefrom10(cid:4)35to10(cid:4)32saftertheBigBang.Collectively,theBig
BangmodelandInflationModelsofcosmologydescribedtheoriginandexpansion
oftheUniverse.
By the mid-1990s, new observations led to new models of cosmology. The
modernStandardModelofCosmology,whichisgenerallyacceptedamongcosmol-
ogists,integratesthefollowingtheories,models,andconcepts:afixedbackground
space-time, the General Theory of Relativity, Dark Matter, Dark Energy, initial
conditionsat Big Bang (best described by InflationaryModels), and the Standard
Model of particle physics. Although the Standard Model of Cosmology has its
own outstandingproblemssuch as Dark Matter and Dark Energy,and issues with
inflation,yetitexplainsalltheobservations.
Todaycosmologistsworkwithsomeofthemostintriguingandyetfundamental
questionssuchas:
(cid:129) WhatistheoverallshapeandsizeoftheUniverse?
(cid:129) WhydidtheUniversestartinanimprobablestate?
(cid:129) Didinflationhappen?
(cid:129) Isthereamultiverse?
(cid:129) WhatistheultimatefateoftheUniverse?
(cid:129) WhatisthetruenatureofDarkEnergy?
(cid:129) CanphysicsdescribewhatwashappeningbeforetheBigBang?
(cid:129) WhathappenstothenotionsofspaceandtimebeforetheBigBang?
Currently there is no single theory that successfully answers all of the above
questions. Beyond the Standard Model of cosmology, speculative theories in
quantumgravity are used to researchsolutionsfor the problemof the selectionof
initialconditionsoftheUniverse.
Thepurposeofthisbookistopresentandexplainthefollowinguniquetopicsin
moderncosmology:
(cid:129) AnovelapproachtouncoverthedarkfacesoftheStandardModelofcosmology.
(cid:129) The possibility that Dark Energy and Dark Matter are manifestations of the
inhomogeneousgeometryofourUniverse.
(cid:129) On the history of cosmological model building and the general architecture of
cosmologicalmodels.
(cid:129) Illustrationsofthelarge-scalestructureoftheUniverse.
(cid:129) AnewperspectiveontheclassicalstaticEinsteinCosmos.
(cid:129) GlobalpropertiesofWorldModelsincludingtheirtopology.
(cid:129) ThearrowoftimeinaUniversewithapositivecosmologicalconstant (cid:2).
Preface ix
(cid:129) Exploringthe consequencesof a fundamentalcosmologicalconstant (cid:2) for our
Universe.
(cid:129) ExploringwhythecurrentobservedaccelerationoftheUniversemaynotbeits
finaldestiny.
(cid:129) Demonstratingthatnatureforbidstheexistenceofapurecosmologicalconstant.
(cid:129) Ourcurrentunderstandingofthelongterm(intimescalesthatgreatlyexceedthe
currentageoftheUniverse)futureoftheUniverse.
(cid:129) The long-term fate and eventual destruction of the astrophysical objects that
populate the Universe – including clusters, galaxies, stars, planets, and black
holes.
(cid:129) All evidence of the Big Bang including the Cosmic Microwave Background
(CMB), and of the existence of other galaxies outside our own will disappear
inabout100billionyears.
The materialis presented in a layperson-friendlylanguagefollowed by additional
technicalsectionsthatexplainthebasicequationsandprinciples.Thisfeatureisvery
attractivetoreaderswhowanttolearnmoreaboutthetheoriesinvolvedbeyondthe
basicdescription.
Each chapter is self-contained. Chapter 3 and Appendix A are related and
collectivelydescribethefutureoftheUniverse.
Chapter1discussesa newperspectiveontheconceptofDarkMatterandDark
Energy. The conventional view on Dark Matter is that these are particles that
respond to the gravitational force, but they do not respond to strong, weak, and
electromagneticforces.Wesimplyjusthavenotdiscoveredthemyet.Whetherthey
will be produced in the near future with LHC experiments at CERN, or detected
withotherexperimentssuchastheCryogenicDarkMatterSearch(CDMS),remains
to be seen. The nature of Dark Energy, however, is more mysterious than that of
Dark Matter. It is believed to be the vacuum energy with negative pressure in its
simplestformthatcausesthe Universeto accelerate.Itaccountsforabout75%of
thematter/energyoftheUniverse.
Chapter1arguesthattheStandardModelofcosmologymaybejusttoosimple,
sinceitassumesthattheUniverseasawholecanbedescribedbythehomogeneous
solutions of Einstein’s equations. The chapter recalls the historical development
of the Standard Model of cosmology and illustrates modern developmentsof our
understanding of the large-scale structure of the Universe. It explains the short-
comingsoftheStandardModelanddevelopsamoregeneralmodelofcosmology
that takes into account the inhomogeneities in the matter distribution, but also in
the geometryof space-time. The tight relations between this geometryand global
propertiesofourUniverse,asimpliedbyafullapplicationoftheGeneralTheoryof
Relativity,providepossiblesolutionstotheDarkEnergyandDarkMatterproblems.
Inthisnewframework,theclassicalUniversemodel,favoredbyEinstein,isputinto
perspectiveand, using this example, the limits and possible generalizationsof the
StandardCosmologicalPrinciplearediscussed.
Chapter 2 investigates the Arrow of Time in a Universe with a positive cos-
mologicalconstant (cid:2). On the observedacceleration of our Universe, the analysis