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.ÿþChapter 27CosmologyVersion 0227.1.pdf, 21 May 2003.Please send comments, suggestions, and errata via email to kip@tapir.calte ch.edu and alsoto rdb@caltech.edu, or on paper to Kip Thorne, 130-33 Caltech, Pasadena CA 91125[NOTE: I have done a quick and incomplete revision of this chapter in light of the recentobservational data from the WMAP satellite (Bennett et.al.2003).I have not had time todo this carefully, nor to absorb fully the WMAP results and incorporate them everywherein the chapter that I should; that must await our next revision. Kip]27.1 OverviewGeneral Relativity is an indispensable foundation for understanding the large scale structureand evolution of the universe (cosmology), but it is only one foundation out of many.Thecrudest of understandings can be achieved with general relativity and little else; but moredetailed and deeper understandings require combining general relativity with quantum fieldtheory, nuclear and atomic physics, thermodynamics, fluid mechanics, and large bodies ofastrophysical lore.In this chapter we shall explore aspects of cosmology which are sufficiently crude that gen-eral relativity, augmented by only bits and pieces of other physics, can provide an adequatefoundation.Our exploration will simultaneously illustrate key aspects of general relativityand give the reader an overview of modern cosmology.We shall begin in Sec.27.2 by discussing the observational data that suggest our universeis homogeneous and isotropic when averaged over regions of space huge compared to clustersof galaxies, and we then shall construct a spacetime metric for an idealized homogeneous,isotropic model for the universe.In Sec.27.3 we shall construct a stress-energy tensor thatdescribes, approximately, the total, averaged energy and pressure of the universe s matterand radiation; and we shall insert that stress-energy tensor and the metric of Sec.27.2 intothe Einstein field equation, thereby deducing a set of equations that govern the evolution ofthe universe.In Sec.27.4 we shall study the predictions that those evolution equations makefor the rate of expansion of the universe and the manner in which the expansion changeswith time, and we shall describe the most important physical processes that have occured1 2in the universe during its evolution into its present state.As we shall see, the details of theexpansion are determined by the values of seven parameters that can be measured todaywith the caveate that there may be some big surprises associated with the so-called darkenergy.In Sec.27.5 we shall describe the astronomical observations by which the universe sseven parameters are being measured, and the multifaceted evidence for dark energy.InSec.27.6 we shall discuss the big-bang singularity in which the universe probably began,and shall discuss the fact that this singularity, like singularities inside black holes, is a signalthat general relativity breaks down and must be replaced by a quantum theory of gravitywhich (hopefully) will not predict singular behavior.We shall also examine a few featuresthat the quantum theory of gravity is likely to exhibit.Finally, in Sec.27.7 we shall discussthe inflationary epoch that the universe appears to have undergone immediately after thequantum gravity, big-bang epoch.27.2 Homogeneity and Isotropy of the Universe;Robertson-Walker Line ElementThe universe obviously is not homogeneous or isotropic in our neighborhood: In our solarsystem (size [ Pobierz caÅ‚ość w formacie PDF ]