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Understanding Cosmology: Exploring the Universe and the Hubble Constant

Dive into the complexities of the Hubble Constant, the expanding universe, and the implications of the Big Bang theory, shaped by Einstein's general theory of relativity. Discover the universe's shape, density, and early conditions.

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Understanding Cosmology: Exploring the Universe and the Hubble Constant

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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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