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PH1600: Introductory AstronomyLecture 21: Geometry of the Universe

PH1600: Introductory AstronomyLecture 21: Geometry of the Universe

Next Lecture: In the Beginning …

School: Michigan Technological UniversityProfessor: Robert Nemiroff

Online Course WebCT pages: http://courses.mtu.edu/

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 1 - 10. HW 11 released later today (Wed) by 4 pm See WebCT at http://courses.mtu.edu/

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 r2

3D: Spheres have volume = 4/3 π r3

Negative curvature 2D: Circles have area > π r2

3D: Spheres have volume > 4/3 π r3

Positive curvature 2D: Circles have area < π r2

3D: Spheres have volume < 4/3 π r3

http://imagine.gsfc.nasa.gov/docs/features/exhibit/map_shape.html

Example: 2D: The Earth

Draw a small circle on your paper It’s area is very close to π r2

Draw a circle the size of Houghton Area still close to π r2

Draw a circle around the Earth Area NOT π r2

Area actually 2 π R2, where R is the distance to the center of the Earth

http://map.gsfc.nasa.gov/m

_mm

/mr_content.htm

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Average Universe Density Determines Universe Curvature

ρcrit = 3 Ho2/(8 pi G)

Ω = ρ / ρcrit

Flat Geometry: Ω = 1 Negative curvature: Ω < 1 Positive curvature: Ω > 1

A Simple Example Universe Made Only of Matter: Ω = ΩM

Open: ΩM > 1 Universe infinite in size Universe will expand forever

Closed: ΩM < 1 Universe finite in size

Can circle the universe! Universe will expand for a while Universe will eventually end in a Big Crunch

Flat: ΩM = 1 Universe infinite in size, always was, always will be Universe will expand forever but stop an infinity

http://physics.uoregon.edu/~courses/BrauImages/Chap26/FG26_009.jpg

Our Accelerating Universe

Supernova cosmology Microwave background Ω = 1

ΩM = 0.3; Ωλ = 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 LightCredit: VIMOS, VLT, ESO APOD: 2002 March 19

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

http://casa.colorado.edu/~ajsh/astr5770_06/sn.htm

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http://en.wikipedia.org/wiki/Image: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 MatterCredit: Richard Mushotzky (GSFC/NASA),

ROSAT, ESA, NASA APOD: April 4, 1999

The Matter of the Bullet ClusterComposite 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 ImagesCredit: 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