Lecture 22: Cosmology- The End of the World as We Know It

Navigation Options

You may :
  • Go to the Astro 106 Main Menu
  • Go to the Class Schedule
  • Look at the Review Questions for Lecture # 22
  • Go to the Lecture # 21 Master Page
  • Go to the Lecture # 23 Master Page

    • Date: April 20, 1995
    Reading Assignment: pp. 591-603

    Description : the Hubble expansion and the formation of the Universe

    Objectives

  • be able to distinguish between the methods in modern cosmology and ancient cosmologies
  • be able to understand the Cosmological Principle
  • be able to understand Olber's paradox
  • be able to relate Hubble's law and the Cosmological Principle to universal expansion
  • be able to distinguish and characterize the three possible future for the universe
  • be able to see the relationships between the average density of the universe, the curvature of space, and the future of the universe

    • Lecture Outline

    Slide # 1: Cosmology

  • the end of the world as we know it
    • Slide # 2: Today's Lecture
  • ancient vs modern cosmology
  • Olber's Paradox
  • Cosmological Principle
  • Hubble's law and Universal Expansion
  • The Future
    • Slide # 3: The Distance Ladder
  • radar
  • parallax
  • spectroscopic parallax
  • Cepheid variables
  • type I supernova, Tully-Fisher
  • Hubble's law
    • Slide # 4: Cosmology
  • the study of the universe
  • the universe
  • all space, time, matter, and energy
    • Slide # 5: Cosmological Questions
  • what was it like in the "old days"
  • early universe
  • what will it be like tomorrow
  • fate of the universe
  • why is it like this now?
    • Slide # 6: Ancient Cosmologies
  • Cosmology has been studied for a long time
    • Slide # 7: Ancient Cosmological Method
  • make observations
  • form hypothesis- interpret data
  • interpretation becomes "reality"
  • if new data conflicts with interpretation
  • discard data
  • revise data
  • supress data
    • Slide # 8: Modern Cosmology- Scientific Method
  • make observation
  • form hypothesis
  • test hypothesis
  • verify or disprove hypothesis
    • Slide # 9: The Scientific Method
  • testing is ESSENTIAL!!!!
  • something is not scientific unless it is subject to experimental verification
    • Slide # 10: Olber's Paradox
  • why is the universe dark?
    • Slide # 11: Lost in a Big Forest (GRAPHICS)
  • everything is the same for a long way in all directions
    • Slide # 12: Lost in a Big Forest (GRAPHICS)
  • every direction you look, you see trees
    • Slide # 13: The Universe
  • assume the universe is infinitely big
  • assume the universe is infinitely old
  • assume the universe is uniform
    • Slide # 14: The Universe (GRAPHICS)
  • everything is the same in all directions
    • Slide # 15: Lost in a Big Universe (GRAPHICS)
  • every direction you look, you see a star's surface
    • Slide # 16: Olber's Paradox
  • if the universe is infinitely old, infinitely large, and uniform
  • why isn't the sky bright?
  • it should be the surface temperature of stars
    • Slide # 17: The Answer
  • the universe cannot be infinitely large or infinitely old
    • Slide # 18: The Cosmological Principle
  • the universe is isotropic and homogeneous
  • we are not in a special place
    • Slide # 19: Isotropic
  • the same in all directions
  • the universe has no preferred directions
    • Slide # 20: Homogeneous
  • at the very largest scales, the universe has is uniform
  • things are pretty much the same all over
  • the same physical concepts apply everywhere
    • Slide # 21: The Cosmological Principle
  • this is an assumption about the universe
  • we will test it
    • Slide # 22: Why?
  • we thought we were in the center of the solar system
  • we were wrong
  • we thought we were in the center of the Galaxy
  • we were wrong
  • we thought we were the ONLY galaxy in the universe
  • we were wrong
    • Slide # 23: Is the universe homogeneous?
  • probably- based on very large studies, it seems to be uniform on 200 Mpc scale
    • Slide # 24: Pencil Beam Surveys (GRAPHICS)
  • redshift survey of a small area in the sky
    • Slide # 25: Is the universe isotropic?
  • yes- it appears to be the same in all directions on very large scales
  • we do see some local motion of our galaxy and cluster of galaxies
    • Slide # 26: Constellation Corner (GRAPHICS)
  • Constellation De Jour
    • Slide # 27: Scorpius (GRAPHICS)
  • July 4 - 11pm - South - 4.0
    • Slide # 28: Scorpius (GRAPHICS)
  • July 4 - 11pm - South - 4.0
    • Slide # 29: Star Maps (GRAPHICS)
  • April 18- midnight- 4.0
    • Slide # 30: Hercules (GRAPHICS)
  • April 18- Midnight- W - 4.0
    • Slide # 31: Hercules (GRAPHICS)
  • April 18- Midnight- W - 4.0
    • Slide # 32: Leo (GRAPHICS)
  • April 18 - Midnight - West - 4.0
    • Slide # 33: Leo (GRAPHICS)
  • April 18 - Midnight - West - 4.0
    • Slide # 34: Cosmological Principle
  • the universe is homogeneous and isotropic
    • Slide # 35: Hubble's Law (GRAPHICS)
  • distant galaxies receed rapidly
  • the greater the distance, the more rapid the recession
    • Slide # 36: Hubble's Law (GRAPHICS)
  • recessional velocity vs distance
    • Slide # 37: Hubble's Law (GRAPHICS)
  • H is the Hubble constant
  • H = 80 km/s/Mpc
    • Slide # 38: Hubble's Law
  • Hubble's law must obey the Cosmological Principle.
  • Everything must be expanding from everything.
    • Slide # 39: Universal Expansion (GRAPHICS)
  • a loaf of bread with raisins
    • Slide # 40: Universal Expansion (GRAPHICS)
  • as the bread rises, the distance between raisins increases
    • Slide # 41: Universal Expansion
  • the amount of expansion depends on the initial distance between raisins
  • the rate of expansion depends on the distance between raisins
    • Slide # 42: The Universe
  • the rate space between galaxies is expanding depends on the distance between t
  • Hubble's law implies UNIVERSAL EXPANSION
    • Slide # 43: Will the Expansion:
  • continue forever
  • stop
  • reverse
    • Slide # 44: Gravity (GRAPHICS)
  • object does not escape
    • Slide # 45: Gravity (GRAPHICS)
  • object escapes
    • Slide # 46: Gravity (GRAPHICS)
  • object does barely escapes
    • Slide # 47: Gravity (GRAPHICS)
  • three possibilities
    • Slide # 48: Gravity and the Universe
  • the total mass of the Universe is slowing the expansion
  • the higher the mass, the more expansion will be slowed down
    • Slide # 49: The Universe (GRAPHICS)
  • three possibilities
    • Slide # 50: Density
  • the total gravity of the universe is determined by its mass
  • the mass is determined by its density and volume
  • if we know the density of the universe, we can determine its fate
    • Slide # 51: Critical Density
  • density needed to close the universe
  • 1029 gm/cm3
  • about 6 hydrogen atoms per cubic meter
    • Slide # 52: Eternal Expansion- Open Universe
  • universe continues to expand forever
  • hydrogen fusion continues in stars
  • hydrogen almost entirely disappears
  • universe becomes cold and dark
    • Slide # 53: Expansion Slows- Flat Universe
  • rate of expansion greatly slows down
  • stars run out of hydrogen
  • universe dies in the cold (again)
    • Slide # 54: Big Crunch- Closed Universe
  • expansion slows and eventually reverses
  • universe shrinks and heats up
  • universe becomes hotter and hotter
  • all life dies
  • universe disappears into a big crunch
    • Slide # 55: Curvature of the Universe
  • if the universe is open, light can travel fo forever
  • universe is infinite in size
  • if it is closed, light cannot escape
  • the universe must bend the path of light by gravity
  • universe if finite in size
    • Slide # 56: Vote for Your Universe
  • open- eternal expansion
  • flat - exactly at critical density
  • close - the Big Crunch
    • Slide # 57: Summary of Observations
  • very high luminosity
  • nonstellar spectra
  • highly variable over short time periods
  • often have jet-like structures
  • emissions lines are very broad
    • Slide # 58: Interpretation
  • lots of energy created in a small area
  • can't be stars- wrong spectra
  • must be strong gravity
  • spectral lines are broad indicating rapid rotation
  • jets may be from an accretion disk