What is this? PH1600: Introductory Astronomy Lecture 21: Geometry of the Universe

PH1600: Introductory Astronomy Lecture 21: Geometry of the Universe Next Lecture: In the Beginning … School: Michigan Technological University Professor: Robert Nemiroff Online Course WebCT pages: This class can be taken online ONLY, class attendance is not required!

You are responsible for… Lecture material Listed wikipedia entries But not higher math APODs posted during the semester APOD review every week during lecture Completing the Quizzes Homework quizzes HW 11 released later today (Wed) by 4 pm See WebCT at

Wikipedia entries: Shape of the universe redshift Dark matter Dark energy Age of the universe

Considering Our Universe as a Whole The Cosmological Principle Universe Homogeneous & Isotropic Homogeneous Smooth when averaged out Example: jello, even fruity jello Isotropic Same in every direction Example: room with the lights out

Possible Geometries of the Universe Flat 2D: Circles have area = π r 2 3D: Spheres have volume = 4/3 π r 3 Negative curvature 2D: Circles have area > π r 2 3D: Spheres have volume > 4/3 π r 3 Positive curvature 2D: Circles have area < π r 2 3D: Spheres have volume < 4/3 π r 3

Example: 2D: The Earth Draw a small circle on your paper Its area is very close to π r 2 Draw a circle the size of Houghton Area still close to π r 2 Draw a circle around the Earth Area NOT π r 2 Area actually 2 π R 2, where R is the distance to the center of the Earth

Average Universe Density Determines Universe Curvature ρ crit = 3 H o 2 /(8 pi G) Ω = ρ / ρ crit Flat Geometry: Ω = 1 Negative curvature: Ω < 1 Positive curvature: Ω > 1

A Simple Example Universe Made Only of Matter: Ω = Ω M Open: Ω M > 1 Universe infinite in size Universe will expand forever Closed: Ω M < 1 Universe finite in size Can circle the universe! Universe will expand for a while Universe will eventually end in a Big Crunch Flat: Ω M = 1 Universe infinite in size, always was, always will be Universe will expand forever but stop an infinity

Our Accelerating Universe Supernova cosmology Microwave background Ω = 1 Ω M = 0.3; Ω λ = 0.7 Universe geometry is flat Universe will expand forever Universe expansion rate is increasing

Possible fates of the universe Big Freeze (current favorite) Big Crunch Big Rip

Breaking Distant Light Credit: VIMOS, VLT, ESO APOD: 2002 March 19

Rumors of a Strange Universe Credit: Adam G. Riess (STScI) et al., NASA APOD: 2004 February 27

Cosmological_composition.jpg

Dark Matter: What is it? Makes up about 30% of universe energy Not seen directly Indicated by the way visible matter moves Spiral galaxies rotate too quickly Clusters of Galaxies would evaporate Clusters of Galaxies show smooth lens effect Composition unknown

Hot Gas and Dark Matter Credit: Richard Mushotzky (GSFC/NASA), ROSAT, ESA, NASA APOD: April 4, 1999

The Matter of the Bullet Cluster Composite Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; APOD: 2006 August 24

Giant Cluster Bends, Breaks Images Credit: W. N. Colley (U. Virginia) et al., HST, NASA APOD: 2004 August 7

Dark Energy: What is it? Dark Matter is NOT Dark Energy Makes up about 70% of Universe energy Repulsive gravitational affects seen Universe accelerating, larger than previously thought Supernova appear too dim to be close Nature and composition unknown

Future of the Universe Stellifereous Era Present day: universe filled with stars Degenerate Era Universe filled with degenerate stellar remnants Black Hole Era Universe filled with black holes Dark Era Universe filled with reshifting light

Will the Universe End in a Big Rip? Illustration Credit & Copyright: Lynette Cook APOD: 2007 October 21