The Universe April 2 2008 Physics 10 UCSD Physics 10 UCSD Beyond Our Comfort Zone Direct Experience 10 5 to 105 meters Dust grain may have 0 01 mm 10 micron diameter View from mountaintop may extend 100 km Experts Experts may claim comfort with 10 7 to 107 m Optical surfaces are smoother than wavelength of light Earth diameter about 12 750 km Scientists 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 m Out Into the Universe An overview of the cosmos What What s out there How big is it Is it getting bigger Spring 2008 Physics 10 UCSD Physics 10 UCSD Graphical Logarithmic Representation of the Physical Scales in our Universe Proton 30 Planck Scale 20 10 Atom Current Experimental Limit To Nearest Star State Cell Outward Journey The logarithmic scale is deceptively compact Phys 10 Student means 10 30 meters 2 0 Comfort Zone 10 Distance To Sun Visible Universe 20 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 distances c 300 000 000 m s 1 light second 3 108 meters 1 light year is about 1016 meters Milky Way 1 yr is about 107 seconds actually 3 15576 107 s Imagine how far you could walk in a given amount of light travel time Does it even mean anything to look beyond the scales represented here This may be all that matters Puts things into a familiar context Gadzooks the Universe is big Spring 2008 Lecture 2 3 Spring 2008 4 1 The Universe April 2 2008 Physics 10 UCSD Physics 10 UCSD Outward Journey Solar System Outward Journey Solar System cont The sun is 1 5 1 5 1011 m away 1 A U The moon is 385 000 km away 1 25 light seconds Walk about 2 meters in this time Across a small room 8 light minutes Walk across campus in this amount of time Pluto is 40 A U away 6x1012 m Spring 2008 Note Deceiving perspective The moon is about 30 earth diameters away from earth Photo from Galileo spacecraft NASA 5 Physics 10 UCSD Pluto Neptune Uranus Saturn Sun Earth Jupiter 5 hours light time Walk to Downtown from here in this time Spring 2008 6 Physics 10 UCSD Outward Journey Solar Neighborhood Outward Journey Milky Way Galaxy Nearest Star to Sun Proxima Centauri Milky Way Galaxy 4 5 light years Walk 5 times around earth at normal walking speed Rings are at 0 5 parsec 1 63 l y intervals 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 live Proxima Centauri is part of the multiple star group labeled Alpha Centauri to the lower right of Sun Other familiar naked eye stars are Sirius and Procyon each on the left edge of the disk Spring 2008 Lecture 2 7 Spring 2008 Not actually our Galaxy but this is what it would look like 8 2 The Universe April 2 2008 Physics 10 UCSD Physics 10 UCSD Outward Journey Extragalactic Outward Journey Extragalactic cont Andromeda Galaxy nearest large spiral Virgo Cluster of galaxies several 1000 members 2 200 000 2 2 million light years away Light we receive today is older than Homo sapiens 50 million light years We re talking dinosaurs now Central Part of Virgo Cluster Spring 2008 Can actually see this galaxy with the naked eye from a dark sky 9 Physics 10 UCSD Spring 2008 10 Physics 10 UCSD The Distribution of Galaxies Large Scale Structure Outward Journey Extragalactic cont Most distant galaxies yet imaged z z 4 12 5 billion light years Older than Earth Sun 90 of Universe age infer 100 billion galaxies in visible Universe The Hubble Deep Field taken by the Hubble Space Telescope in 1995 Almost all objects are galaxies save one foreground star just to upper left of center Most galaxies are lower redshift z 1 but some of the smaller more distant galaxies are z 3 www pbs org wgbh nova universe tour ggsn05 html oposite stsci edu pubinfo PR 96 01 html Spring 2008 Lecture 2 11 10 000 Milky Ways would fit across a typical void Spring 2008 12 3 The Universe April 2 2008 Physics 10 UCSD Physics 10 UCSD Telescopes as Time Machines Early Galaxies More distant galaxies are old galaxies Takes time for light to reach us 12 billion light years away means we see it as it was 12 billion years ago Messy Train Wrecks Bigger telescopes better technology see farther back in time and guess what galaxies don t look like they used to All are distorted due to collisions and mergers we can see galaxies in the process of forming bottom up construction built up by collisions mergers Spring 2008 13 Physics 10 UCSD Spring 2008 14 Physics 10 UCSD The Big Bang Expansion Example The Universe is expanding like a sponge The farther the galaxy the faster it appears to recede Not expanding into anything space itself is expanding There is no center where the explosion took place Everything is simply getting farther from everything else as the space between swells This is true for light waves as well leading to redshifted light Not true for bound objects galaxy solar system earth meter stick human brain If we run the movie in reverse must must ve started out very small thus the Big Bang idea Spring 2008 Lecture 2 15 Spring 2008 16 4 The Universe April 2 2008 Physics 10 UCSD Physics 10 UCSD Cosmic Expansion Redshifts Light Useful Analogies and their limits Balloon being inflated Close Recent good points if confined to surface there is no center of expansion each galaxy sees all others receding space itself is what s expanding can represent closed geometry Far Ancient flaws little pictures of galaxies expand too which is inaccurate Light from far away has more time to stretch Raisin Bread baking good points Light from nearby sources gets stretched less raisins all move farther from each other as bread expands 3 dimensional expansion of space bread dough galaxies raisins themselves do not expand Longer wavelength redder light far away light more redshifted flaws bounded has edge expands into environment Spring 2008 17 Physics 10 UCSD Spring 2008 Physics 10 UCSD Redshifts Illustrated Hubble Hubble s Expansion Law Galaxies have identifiable usually unambiguous spectral features from specific atoms that serve as wavelength references These features get pushed out toward the red the farther away they are To the left are spectra of quasars galaxies with active black holes at a variety of redshifts The farther away the galaxy the bigger the redshift Redshift is often treated like a Doppler velocity Apparent speed at which