Out Into the UniverseBeyond Our Comfort ZoneGraphical Logarithmic Representation of the Physical Scales in our UniverseOutward JourneyOutward Journey; Solar SystemOutward Journey; Solar System, cont.Outward Journey; Solar NeighborhoodOutward Journey; Milky Way GalaxyOutward Journey, ExtragalacticOutward Journey; Extragalactic, cont.Slide 11PowerPoint PresentationTelescopes as Time MachinesEarly GalaxiesThe Big BangExpansion ExampleUseful Analogies (and their limits)Slide 18Redshifts IllustratedHubble’s Expansion LawReferences and AssignmentUCSDPhysics 10Out Into the UniverseOut Into the UniverseAn overview of the cosmos:An overview of the cosmos:What’s out there?What’s out there?How big is it? Is it getting bigger?How big is it? Is it getting bigger?Spring 2008 2UCSDPhysics 10Beyond Our Comfort ZoneBeyond Our Comfort Zone•Direct Experience: 10Direct Experience: 10-5-5 to 10 to 1055 meters meters–Dust grain may have 0.01 mm = 10 micron diameter–View from mountaintop may extend 100 km•““Experts” may claim comfort with 10Experts” may claim comfort with 10-7-7 to 10 to 1077 m m–Optical surfaces are smoother than wavelength of light–Earth diameter about 12,750 km•Scientists today deal with much larger rangesScientists today deal with much larger ranges–Particle physics probes 10-18 m scales–Visible Universe spans 1026 m–Theorists stop at “Planck scale”; 10-35 mSpring 2008 3UCSDPhysics 10Graphical Logarithmic RepresentationGraphical Logarithmic Representationof the Physical Scales in our Universeof the Physical Scales in our Universe-30 -20 -10 0 10 20ComfortZonePlanckScaleCurrentExperimentalLimitProtonAtomCellPhys 10StudentStateDistanceTo SunTo NearestStarMilkyWayVisibleUniversemeans 10-30 metersDoes it even mean anything to look beyond the scales represented here?This may be all that matters!Spring 2008 4UCSDPhysics 10Outward JourneyOutward Journey•The logarithmic scale is deceptively compactThe logarithmic scale is deceptively compact–We think linearly, because that’s how we perceive time–Now let’s imagine the universe in linear terms…•We use the speed of light to express large distancesWe use the speed of light to express large distances–c =300,000,000 m/s: 1 light second = 3108 meters–1 light year is about 1016 meters•1 yr is about  107 seconds (actually 3.15576107 s)•Imagine how far you could walk in a given amount Imagine how far you could walk in a given amount of light travel-timeof light travel-time–Puts things into a familiar context–Gadzooks, the Universe is big!Spring 2008 5UCSDPhysics 10Outward Journey; Solar SystemOutward Journey; Solar System•The moon is 385,000 km awayThe moon is 385,000 km away–1.25 light seconds–Walk about 2 meters in this time: Across a small roomNote: Deceiving perspective. The moon is about 30 earth-diametersaway from earth. Photo from Galileo spacecraft (NASA).Spring 2008 6UCSDPhysics 10Outward Journey; Solar System, cont.Outward Journey; Solar System, cont.•The sun is 1.5The sun is 1.510101111 m away (1 A.U.) m away (1 A.U.)–8 light minutes–Walk across campus in this amount of time•Pluto is 40 A.U. away: 6x10Pluto is 40 A.U. away: 6x101212 m m–5 hours light time–Walk to Downtown from here in this timeSunEarthJupiterSaturnUranusNeptunePlutoSpring 2008 7UCSDPhysics 10Outward Journey; Solar NeighborhoodOutward Journey; Solar Neighborhood•Nearest Star to Sun: Proxima CentauriNearest Star to Sun: Proxima Centauri–4.5 light years–Walk 5 times around earth at normal walking speed!Rings are at 0.5 parsec(=1.63 l.y.) intervals.Proxima Centauri is partof the multiple star grouplabeled Alpha Centauri,to the lower right of Sun.Other, familiar naked-eyestars are Sirius and Procyon,each on the left edge of thedisk.Spring 2008 8UCSDPhysics 10Outward Journey; Milky Way GalaxyOutward Journey; Milky Way Galaxy• Milky Way GalaxyMilky Way Galaxy–20,000 light years to center from here–Forget about walking—try even living that long!–100,000 light years in diameter–disk is a few hundred light years thick where we liveNot actually our Galaxy, but this is what it would look like.Spring 2008 9UCSDPhysics 10Outward Journey, ExtragalacticOutward Journey, Extragalactic•Andromeda Galaxy (nearest large spiral)Andromeda Galaxy (nearest large spiral)–2,200,000 (2.2 million) light years away–Light we receive today is older than Homo sapiensCan actually see this galaxy with the naked eye from a dark sky!Spring 2008 10UCSDPhysics 10Outward Journey; Extragalactic, cont.Outward Journey; Extragalactic, cont.•Virgo Cluster of galaxies (several 1000 members)Virgo Cluster of galaxies (several 1000 members)–50 million light years–We’re talking dinosaurs now…Central Part of Virgo ClusterSpring 2008 11UCSDPhysics 10Outward Journey; Extragalactic, cont.Outward Journey; Extragalactic, cont.•Most distant galaxies yet imaged (Most distant galaxies yet imaged (zz  4) 4)–12.5 billion light years–Older than Earth/Sun; 90% of Universe age–infer 100 billion galaxies in visible UniverseThe Hubble Deep Field, taken by the Hubble SpaceTelescope in 1995.Almost all objects are galaxies, save one foregroundstar just to upper left of center.Most galaxies are lower redshift (z < 1), but someof the smaller, more distant galaxies are z > 3.www.pbs.org/wgbh/nova/universe/tour_ggsn05.htmloposite.stsci.edu/pubinfo/PR/96/01.htmlSpring 2008 12UCSDPhysics 10The Distribution of Galaxies: Large Scale Structure10,000 Milky Ways would fit across a typical voidSpring 2008 13UCSDPhysics 10Telescopes as Time MachinesTelescopes as Time Machines•More distant galaxies are More distant galaxies are oldold galaxies galaxies–Takes time for light to reach us–12 billion light years away means we see it as it was 12 billion years ago•Bigger telescopes, better technology Bigger telescopes, better technology  see farther see farther back in timeback in time–and guess what—galaxies don’t look like they used to•we can see galaxies in the process of forming•bottom-up construction, built up by collisions/mergersSpring 2008 14UCSDPhysics 10Early GalaxiesEarly GalaxiesMessy TrainWrecks!All are distorteddue to collisionsand mergersSpring 2008 15UCSDPhysics 10The Big BangThe Big Bang•The Universe is expanding like a spongeThe Universe is expanding like a sponge–The farther the galaxy, the faster it appears to recede–Not expanding into anything, space itself is