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  • Chapter 18: Cosmology

    For a humorous approach to quarks, check out the Jefferson Labs game. In Looking for the Top Quark, each player receives six quarks that they hide on a grid. The players use coordinates to find their opponent's hidden quarks. The first player to find all six of their opponent's quarks wins! education.jlab.org/topquarkgame/ Information on the Planck mission will be found at www.esa.int/science/planck.

  • WHAT DO YOU THINK?What does the Universe include?Did the Universe have a beginning?Is the Universe expanding, fixed in size, or contracting?Will the Universe last forever?

  • You will discoverCosmology, which seeks to explain how the Universe began, how it evolves, and its fate.The best theory we have for the evolution of the Universe the Big Bang.How astronomers explain the overall structure of the Universe.Our understanding of the fate of the Universe.

  • In the Beginning the Big BangThe Universe began 13.7 billion years ago with an event called the Big Bang.All of space-time, matter, and energy were created at the Big Bang.The left-over energy from the Big Bang can be detected today as the Cosmic Microwave Background Radiation.The temperature of this radiation is only a few degrees above absolute zero.

  • The Beginning The Big Bang

  • In Search of The Earliest PhotonsWilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001

    FIGURE 18-3 In Search of Primordial Photons (a) TheWilkinson Microwave Anisotropy Probe (WMAP) satellite, launchedin 2001, improved upon the measurements of the spectrum andangular distribution of the cosmic microwave background takenby the COBE satellite. (b) The balloon-carried telescopeBOOMERANG orbited above Antarctica for 10 days collecting dataused to resolve the cosmic microwave background with 10 timeshigher resolution than that of COBE. All these experiments foundlocal temperature variations across the sky, but no overalldeviation from a perfect blackbody spectrum. (a: NASA/WMAPScience Team b: The BOOMERANG Group, University of California, SantaBarbara)

  • WMAPs Baby Picture of the Universe Cosmic Microwave Background Radiation

  • The Universe is ExpandingThe Redshift of Superclusters shows us that the Universe is expanding. This Redshift is called the Cosmological Redshift, because it is caused by the expansion of space.The farther away a galaxy is from us, the faster it moves away from us.

  • The Expansion of the Universe Cosmological RedshiftSpace itself is expanding.

    FIGURE 18-1 Cosmological Redshift Just as the waves drawnon this rubber band are stretched along with the rubber band,so too are the wavelengths of photons stretched as the universeexpands.

  • Expanding Cake AnalogyJust as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies move away from each other as the space of the Universe expands.

    The Expanding Chocolate Chip CakeAnalogy The expanding universe can becompared to a chocolate chip cake bakingand expanding in the Space Shuttles microwave oven. Justas all the chocolate chips move apart asthe cake rises, all the superclusters ofgalaxies recede from each other as theuniverse expands.

  • The Observable UniverseThe cosmic light horizon today is about 13.7 billion light-years away in all directions.

    FIGURE 18-14 The Observable UniverseThis diagram shows why we only see partof the entire universe. As time passes, thisvolume grows, meaning that light frommore distant galaxies reaches us. Thegalaxies we see at the farthest reaches ofour telescopes resolving power are as theywere within a few hundred million yearsafter the Big Bang (see inset). Thesegalaxies, formed at the same time as theMilky Way, appear young because the lightfrom their beginnings is just now reachingus. The radius of the cosmic light horizon isequal to the distance that light has traveledsince the Big Bang. Because the Big Bangoccurred about 13.8 billion years ago,the cosmic light horizon today is about13.8 billion light-years away in all directions.Inset: This image of the Hubble Deep Fieldshows some of the most distant galaxieswe have seen. (inset: Robert Williams and theHubble Deep Field Team, STScI and NASA)

  • HST Galaxies >13 Billion LY AwayThis HST Ultra Deep Field Telescope image shows some of the most distant galaxies we have seen.

    FIGURE 16-32 Distant Galaxies (a) The young cluster ofgalaxies MS1054-03, shown on the left, contains many orbitingpairs of galaxies, as well as remnants of recent galaxy collisions.Several of these systems are shown at the right. This cluster islocated 8 billion light-years away from Earth. (b) This image ofmore than 300 spiral, elliptical, and irregular galaxies containsseveral that are an estimated 12 billion light-years from Earth.Two of the most distant galaxies are shown in the images on theright, colored in red at the centers of the pictures. (a, b: P. VanDokkum, Uner of Granengen, ESA and NASA)

  • Early Universe Temperature VariationsTiny temperature fluctuations in the Cosmic Microwave Background Radiation are related to the large-scale structure of the Universe today, indicating where Superclusters and voids grew.

    FIGURE 18-15 Structure of theEarly Universe This microwavemap of the entire sky, producedfrom data taken by the WilkinsonMicrowave Anisotropy Probe(WMAP), shows temperaturevariations in the cosmic microwavebackground. Red regions are about0.00003 K warmer than theaverage temperature of 2.73 K; blueregions are about 0.00003 K coolerthan the average. Inset: These tinytemperature fluctuations, observedby BOOMERANG, are related to thelarge-scale structure of theuniverse today, indicating wheresuperclusters and voids grew. Theradiation detected to make this mapis from a time 379,000 years afterthe Big Bang. (NASA/WMAP ScienceTeam; inset: NSF/NASA)

  • The First Stars much larger than the Sun with much shorter livesThe burst of star formation that occurred within a few hundred million years after the Big Bang.

    FIGURE 18-16 Galaxies Forming by Combining Smaller Units(a) This painting indicates how astronomers visualize the burst ofstar formation that occurred within a few hundred million yearsafter the Big Bang. The arcs and irregular circles representinterstellar gas that is illuminated by supernovae. (b) Using theHubble and Keck telescopes, astronomers discovered two groups ofstars (arrows) 13.4 Bly away that are believed to be protogalaxies,from which bigger galaxies grew. These protogalaxies werediscovered because they were enlarged by the gravitational lensingof an intervening cluster of galaxies. (c) The Chandra X-raytelescope imaged gravitationally bound gas around the distantgalaxy 3C 294. The X-ray emission from this gas is the signature ofan extremely massive cluster of galaxies, in this case at a distanceof about 11.2 Bly from us. (a: Adolf Schaller, STScI/NASA/K. Lanzetta,SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib (Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

  • Proto-Galaxy FormationHubble and Keck telescope images of two groups of stars that are believed to be proto-galaxies, from which bigger galaxies grew

    FIGURE 18-16 Galaxies Forming by Combining Smaller Units(a) This painting indicates how astronomers visualize the burst ofstar formation that occurred within a few hundred million yearsafter the Big Bang. The arcs and irregular circles representinterstellar gas that is illuminated by supernovae. (b) Using theHubble and Keck telescopes, astronomers discovered two groups ofstars (arrows) 13.4 Bly away that are believed to be protogalaxies,from which bigger galaxies grew. These protogalaxies werediscovered because they were enlarged by the gravitational lensingof an intervening cluster of galaxies. (c) The Chandra X-raytelescope imaged gravitationally bound gas around the distantgalaxy 3C 294. The X-ray emission from this gas is the signature ofan extremely massive cluster of galaxies, in this case at a distanceof about 11.2 Bly from us. (a: Adolf Schaller, STScI/NASA/K. Lanzetta,SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib (Observatorie Midi-Pyrenees, France), NASA, ESA; c: NASA)

  • Creation of Spiral and Elliptical GalaxiesA galaxy begins as a huge cloud of primordial gas that collapses gravitationally.If the rate of star formation was low, then a spiral galaxy formed.

    If the rate of star formation was high, then an elliptical galaxy formed.

    FIGURE 18-18 The Creation of Spiral andElliptical Galaxies A galaxy begins as a hugecloud of primordial gas that collapsesgravitationally. (a) If the rate of star birth is low,then much of the gas collapses to form a disk,and a spiral galaxy is created. (b) If the rate ofstar birth is high, then the gas is converted intostars before a disk can form, resulting in anelliptical galaxy.

  • The Fate of the UniverseThe fate of the Universe depends on the shape of space-time.The shape of space-time is determined by how much total matter and energy there is in the Universe.Space-time could have one of three shapes:

    Sphere = positive curvature = closed.Our floor = no curvature = flat.Saddle = negative curvature = open.

  • Possible Shapes of Space-time,and the Fate of the UniverseClosed Universe would collapse.

    Flat Universe could slowly expand forever.

    Open Universe would expand forever.

    FIGURE 18-20 The Possible Geometries of the Universe Theshape of space (represented here as two-dimensional for ease ofvisualization) is determined by the matter and energy contained inthe universe. The curvature is either (a) positive, (b) zero, or(c) negative, depending on whether the average matter and energydensity throughout space is greater than, equal to, or less than acritical value. The lines on each