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Galaxies and the Universe

Galaxies and the Universe. What Are Galaxies?. Greek galax = milk William Herschel, 1783: A disk with the Sun slightly off-center. What Are Galaxies?. 19th Century: “Spiral Nebulae” Nearby? Maybe Solar Systems in Formation? 1920: Galaxies are Stars 1920’s: Galaxies are like the Milky Way

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Galaxies and the Universe

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  1. Galaxies and the Universe

  2. What Are Galaxies? • Greek galax = milk • William Herschel, 1783: A disk with the Sun slightly off-center

  3. What Are Galaxies? • 19th Century: “Spiral Nebulae” • Nearby? Maybe Solar Systems in Formation? • 1920: Galaxies are Stars • 1920’s: Galaxies are like the Milky Way • Biggest single increase in our mental picture of the Universe in human history

  4. Where Are We in our Galaxy? • The visible Milky Way suggests our galaxy is a flat disk • Surrounding other galaxies is a spherical halo of Globular Star Clusters

  5. Galaxies and Globular Clusters

  6. The Milky Way’s Globular Clusters

  7. The Milky Way As We See It

  8. Anatomy of a Galaxy

  9. Spiral Arms

  10. In Microwaves, We Can See the Hub of the Galaxy

  11. Mapping the Neighborhood

  12. Mapping the Neighborhood

  13. Mapping the Galaxy: Not There Yet

  14. Mapping the Galaxy: Not There Yet

  15. The Local Group

  16. Downtown: The Virgo Cluster: 50 m.l.y

  17. The Local Super-cluster

  18. The Coma Cluster350 m.l.y.

  19. Large-Scale Structure of the Universe to 500 m.l.y.

  20. Travel to the Stars? • Kinetic Energy = 1/2 Mv2 • What does it take to get a 1000-ton spaceship to 10% of the speed of light? (43 years to Alpha Centauri) • M=106 kg, v = 3 x 107 m/sec • KE = 1/2 x 106 x 9 x 1014 = 4.5 x 1020 joules • Equals U.S. Energy Production for 4.5 years • Once you get there, you have to stop.

  21. Relativity • Speed of Light is Independent of Source • Michelson and Morley, 1887 - Speed of Light Independent of Observer • “One of the Most Unexpected Results in the History of Science” - Isaac Asimov • Conclusion: Speed of Light is the Same for All Observers • Implication: Space and Time Must Change to Keep Speed of Light Constant

  22. Why the Speed of Light is a Speed Limit • Energy of a Moving Object in Relativity:E = mc2------------------------------------------------------------------------------- 1 - v2/c2 • One consequence: as v approaches c, Energy goes to infinity • Also, as we approach c, Energy goes up very fast

  23. Fuel Economy of a Starship • At 0.1 c, energy is 0.7% greater than Newtonian formula • At 0.5 c, 24% greater • At 0.9 c, 3 x greater • At 0.99 c, 12 x greater • At 0.999 c, 43 x greater • Each extra 9 more than triples the energy • Getting our 1000 ton ship to 0.9 c takes 1.1 x 1023 joules = U.S. energy use for 1100 years

  24. Another Consequence of Relativity- Gravitational Lenses

  25. What Does The Universe Look Like?

  26. What Does The Universe Look Like?

  27. “The Big Bang” • Edwin Hubble, Recession of Galaxies, 1929 • Red-shift increases with distance • Cosmic Microwave Background, 1965 • Estimated Age of Universe: 12-15 b.y. • “Big Bang” originally a derisive term, coined by Fred Hoyle

  28. As Far Out as We Can See - Ten Days With the Hubble Telescope

  29. A New Name for the “Big Bang?”(Sky and Telescope, 1995) • The Big Boot • God’s Log-On • Fred Withair Day (“Nobody ever named anything else after me, so why not?”) • What Happens If I Push This Button? • You’re Never Going To Get It All Back In There Again

  30. 90% of the Universe is “Missing” • Outer Stars in Galaxies revolve faster than expected • What holds clusters of galaxies together? • Conclusion: There must be a lot of invisible mass in the Universe • Not really “missing”, just non-luminous

  31. Astronomers Are Not As Upset As One Might Expect • MACHO’s (Massive Compact Halo Objects): faint stars, brown dwarfs, planets • Cool non-luminous gas • Massive Neutrinos? • WIMP’s (Weakly Interacting Massive Particles) • Magnetic monopoles • Exotic objects: strings, mini-black holes

  32. Fine Tuning the Universe • Density • Much greater and the Universe would already have collapsed in on itself • Much less and stars could not have formed • Nuclear Forces • Fusion impossible • Fusion too easy • Anthropic Principle • Cosmology has to be able to explain why we exist

  33. Fine Tuning the Universe • It just came out that way • It has to be that way for reasons we haven’t yet discovered • Maybe there are an infinity of universes but only those with certain parameters develop intelligent life (Multiverse) • Engineered or designed

  34. Fine Tuning the Universe • Designer? • Doesn’t Explain Anything • If the Designer can create a Universe, why is c = 300,000 km/sec instead of 400,000? • If Designer had to have c = 300,000 km/sec, why? What (who?) dictated that, and why? • Who says Designer is anything pictured by any religion?

  35. Misinterpreting Relativity • There are no absolutes • Speed of light is absolute • It may not be possible to be absolutely right but it is very easy to be absolutely wrong

  36. Where Will It All End? • Trillions of years: Star formation ends • 10-100 trillion years: Stars stop radiating • 1015 – 1020 years: Planetary orbits decay • 1032 – 1041 years: Protons decay? • Heat Death? • Big Crunch? • Big Bounce?

  37. What Does Cosmology Imply for Philosophy? • Nothing • At Least, Not Yet • It Is Hopelessly Premature To Try To Create A Philosophy Based on Cosmology • We can say what the fate of the Universe will be based on specific assumptions • We are a long way from knowing the assumptions are complete or correct • If you support your philosophy with science, be prepared for science to prove it wrong

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