what is this? ph1600: introductory astronomy lecture 21: geometry of the universe
TRANSCRIPT
What is this?
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