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ASTR 1102-002 2008 Fall Semester

ASTR 1102-002 2008 Fall Semester. Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture22]. Chapter 26 : Cosmology and Chapter 27: Exploring the Universe. The “Hubble Constant” H 0. Let’s examine more closely the meaning of the so-called “Hubble Constant,” H 0

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ASTR 1102-002 2008 Fall Semester

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  1. ASTR 1102-0022008 Fall Semester Joel E. Tohline, Alumni Professor Office: 247 Nicholson Hall [Slides from Lecture22]

  2. Chapter 26: CosmologyandChapter 27: Exploring the Universe

  3. The “Hubble Constant” H0 • Let’s examine more closely the meaning of the so-called “Hubble Constant,” H0 • H0 = (73 km/s)/Mpc = (73 km/s)/(3.085 x 1019 km) = 2.37 x 10-18 /s • That is, 1/H0 = 4.23 x 1017 s = 13.4 billion yrs

  4. Interpretation of Hubble’s Law • Hubble’s Law appears to put us in a special location in the Universe: Everything appears to be expanding away from us! • Einstein’s general theory of relativity provides a context for interpreting (& understanding) Hubble’s Law that does not put us in a special location.

  5. §26-2: Universe is Expanding • Natural solution to Einstein’s general theory of relativity • Motivated by the “Hubble Law” observations • How to picture what’s going on: • Expanding chocolate chip cake analogy • Expanding balloon

  6. §26-2: Universe is Expanding • Natural solution to Einstein’s general theory of relativity • Motivated by the “Hubble Law” observations • How to picture what’s going on: • Expanding chocolate chip cake analogy • Expanding balloon analogy

  7. §26-6: Shape of the Universe • Curvature • Flat (e.g., expanding cake analogy) • Positive curvature (e.g., sphere/balloon) • Negative curvature (e.g., saddle-shaped) • Critical density rc = (3H02)/(8pG) • Density parameter W0 = r0/rc, where r0 is the current average density of matter in the universe

  8. Circumference of circle = 2pr

  9. Circumference of circle < 2pr

  10. Circumference of circle > 2pr

  11. §26-6: Shape of the Universe • Curvature • Flat (e.g., expanding cake analogy) • Positive curvature (e.g., sphere/balloon) • Negative curvature (e.g., saddle-shaped) • Critical density rc = (3H02)/(8pG) • Density parameter W0 = r0/rc, where r0 is the current average density of matter in the universe

  12. How Do We Measure W0 ? • Measure (count up) all the matter density in the universe (r0) and compare the value to rc. • Measure distances and redshifts of even more distant galaxies and look for deviations in the Hubble diagram.

  13. How Do We Measure W0 ? • Measure (count up) all the matter density in the universe (r0) and compare the value to rc. • Measure distances and redshifts of even more distant galaxies and look for deviations in the Hubble diagram.

  14. How Do We Measure W0 ? • Measure (count up) all the matter density in the universe (r0) and compare the value to rc. • Measure distances and redshifts of even more distant galaxies and look for deviations in the Hubble diagram.

  15. Implications  Big Bang • About 13.4 billion years ago, the universe must have been very dense, hot, and rapidly expanding • “Big Bang” origin of the universe! • What are other implications of this model? Specifically, what were conditions like in the very early universe, and can we test our predictions?

  16. Implications of Big Bang • Era of “recombination” and “Cosmic Microwave Background (CMB)” • Origin of the Elements • Non-uniformities in the Early Universe and the Origin of Galaxies

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