Lecture 26

Lecture 26 - Today (Weds.) in Astro 3 Cell phones on...

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Today (Weds.) in Today (Weds.) in Astro Astro 3 3 z Cell phones on vibrate… z The Plan: Í (last extra credit planetarium/telescope opportunity tonight) Í Quiz 10 (will be posted today) on Chapters 16 and 17 due Monday 11 p.m. Í Today: start Chapter 17 “Cosmology”. Í Also fill out course evaluations
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Units of Chapter 17 The Universe on the Largest Scales The Expanding Universe Cosmic Dynamics and the Geometry of Space The Fate of the Cosmos The Early Universe The Formation of Nuclei and Atoms Cosmic Inflation The Formation of Large-Scale Structure in the Universe
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17.1 The Universe on the Largest Scales This galaxy map shows the largest structure known in the Universe, the Sloan Great Wall . No structure larger than 300 Mpc is seen.
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17.1 The Universe on the Largest Scales Therefore, the Universe is homogenous (any 300-Mpc-square block appears much like any other) on scales greater than about 300 Mpc. The Universe also appears to be isotropic –the same in all directions. (The cosmological principle includes the assumptions of isotropy and homogeneity .)
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17.2 The Expanding Universe Olbers’s Paradox : If the universe is homogeneous , isotropic , infinite , and unchanging , the entire sky should be as bright as the surface of the Sun.
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17.2 The Expanding Universe So, why is it dark at night? The universe is homogeneous and isotropic It must not be infinite and/or unchanging . We have already found that galaxies are moving faster away from us the farther away they are:
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17.2 The Expanding Universe So, how long did it take the galaxies to get there?
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Using we find that time is about 14 billion years. Note that
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Lecture 26 - Today (Weds.) in Astro 3 Cell phones on...

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