Cosmology

							 The Beginning of Time




Somewhere, something incredible
    is waiting to be known.
           - Carl Sagan
       WHAT DO YOU THINK?

1.   Did the universe have a beginning?
2.   Into what is the universe expanding?
3.   Will the universe last forever?
4.   Are there other universes?
5.   Can we ever find out what started everything?
6.   Should we try??
    In this chapter you will discover…
   Cosmology, which seeks to explain how the
    universe began, how it evolves, and its fate

   the best theory that we have for the evolution of
    the universe—the Big Bang

   how astronomers trace the emergence of matter
    and the formation of galaxies
    In this chapter you will discover…
   Cosmology, which seeks to explain how
    the universe began, how it evolves, and its
    fate

   How astronomers explain the overall
    structure of the universe

   Our understanding of the fate of the
    universe
      Key Essay Questions


 How did the universe begin?
 How will it end?
 How do we know?
 What evidence do we have?
                     Facts
    Must be explained by a scientific theory to
                 be considered


   Quasars more prevalent far away; we
    don’t see them beyond ~ 13 Billion light
    years.

   Cosmic Microwave Background Radiation
                      Facts
    Must be explained by a scientific theory to
                 be considered

   The Night Sky is Dark (Olber’s Paradox)

   Hubble’s Law: Distant Galaxies move away from
    us, faster. The Universe is changing in time.

   90% of the Universe is Hydrogen, 10% is Helium
Olber’s Paradox – Why is the Night
            Sky Dark?


 If the universe contains an infinite number
  of stars, uniformly distributed in space,
  and the universe is infinitely old, then:
Olber’s Paradox – Why is the Night
            Sky Dark?
   If the universe contains an infinite number of stars, uniformly
    distributed in space, and the universe is infinitely old, then:
        Overall brightness received in any direction from
         those stars is constant.
        Farther away, more space, but more stars in that
         space.
        In every direction, eventually look at surface of a star,
         so….
        Every point in the sky should be as bright as the
         surface of a star.
            Olber’s Paradox
          If…then logical argument
           assumption  conclusion

Clearly the night sky IS dark
The conclusion is false so one or more
  assumptions must be incorrect!
The universe is not infinite in size, and not
  infinite in age!
                        Facts
    Must be explained by a scientific theory to
                 be considered

   The Night Sky is Dark (Olber’s Paradox)
   Hubble’s Law: Distant Galaxies move away from us,
    faster. The Universe is changing in time.
   90% of the Universe is Hydrogen, 10% is Helium
   Quasars more prevalent far away; we don’t see them
    beyond ~ 13 Billion light years.
   Cosmic Microwave Background Radiation
Penzias & Wilson’s Horn
Antenna used to discover
        CMBR
WMAP satellite (2001)
Boomerang Balloon-Lofted Probe
 above Antarctica (1998 & 2003)
    What is the Cosmic Microwave
             Background?
 Relic ―heat‖ energy from Big Bang
 Released ~ 1/2 million years after Bang
     Earlier, universe = ―sea‖ of high energy
      particles & photons
     After, universe cooled allowing neutral matter
      to form
 Radiation then is visible through space
 Redshifted as universe expands
                        Facts
    Must be explained by a scientific theory to
                 be considered

   The Night Sky is Dark (Olber’s Paradox)
   Hubble’s Law: Distant Galaxies move away from us,
    faster. The Universe is changing in time.
   90% of the Universe is Hydrogen, 10% is Helium
   Cosmic Microwave Background Radiation
   Quasars more prevalent far away; we don’t see them
    beyond ~ 13 Billion light years.
                  Assumptions

   Physics: The laws we know of around us work
    everywhere in the same way.

   Isotropy: The Universe looks the same as it appears to
    us – everywhere

   Homogeneity: The Universe is made of the same stuff
    we see around us - everywhere
Facts + Assumptions Theory
   The Big Bang Theory

       The universe started ~ 14 Billion years ago

       All energy, incredibly hot and dense

       Expands incredibly fast (inflation)

       Matter (protons, electrons, neutrons) created
        from energy (E = mc2)
Facts + Assumptions Theory
   The Big Bang Theory

       Some protons (Hydrogen) fuse to create Helium

       Universe cools and expands

       Eventually, neutral atoms form…

       ―Recombination‖ era is when CBR can be seen
A Big Bang Timeline…
              The Details…. 
   What would the universe have been like in
    the first few …
     billionths of billionths of a second?
     Seconds?
     Three Minutes?

 Why did the universe expand so quickly?
 When did galaxies form?
 Why did galaxies form?
    Conditions in the Early Universe

   The most distant quasars and galaxies we
    observe come from a time when the Universe
    was a billion years old.

   The cosmic microwave background prevents us
    viewing light from before the Universe was
    ~400,000 years old.

   So how do we know what conditions were like at
    the beginning of time?
      Conditions in the Early Universe

   Know conditions & expansion
    rate of the Universe today.

   By running the expansion
    backwards, model the early
    universe
    Conditions in the Early Universe

•   predict temperature & density of
    Universe at anytime in its history
    using basic physics

•   study how matter behaves at high
    temperatures & densities in
    laboratory experiments

•   current experimental evidence
    provides info on conditions as early
    as 10–10 sec after the Big Bang
          The Creation of Matter

 The early Universe was filled with radiation &
  subatomic particles.
 E = mc2 is a two-way street!



If T >    1012   K                   matter
                             p+
                                      n       e -

                                -
                             p       n       e +
                                    antimatter
       The Destruction of Matter

 When two identical particles of matter &
 antimatter collide

 •   they annihilate & form gamma photons
          The Destruction of Matter

   During first few moments of the Universe…

    •   matter and radiation (energy) were
        continually converting into each other

    •   the total amount of mass-energy remained
        constant
         (small details about)   The Big Bang
                                        –43
            Planck Era (t < 10                sec)
   Because we are as yet unable to link…
    • quantum mechanics (our successful theory of
      the very small)
    • general relativity (our successful theory of the
      very large)
   Can’t yet describe what happened in this era.
   We suppose that all four natural forces
    were unified during this era.
            (small details about)   The Big Bang
                                    –43          –38
            GUT Era (10                   < t < 10     sec)

   The Universe contained two natural
    forces:

    •   Gravity
    •   Grand Unified Theory (GUT) force
         electromagnetic + strong (nuclear) + weak forces
           unified
          (small details about)   The Big Bang
                                  –43          –38
          GUT Era (10                   < t < 10         sec)

                                                   –38
   Lasted until Universe was 10                         sec old.
                                                             29
    •   at this time, Universe had cooled to 10 K
    •   strong force emerges separate and distinct
        from electro-weak force
    •   the energy released by this caused a sudden
        and dramatic inflation of the size of the
        Universe
         (small details about)   The Big Bang
                                    –38          –10
    Electroweak Era (10                   < t < 10     sec)


   Universe contained three natural forces:
    gravity, strong, & electroweak

                                               –10
   Lasted until Universe was 10                     sec old.
                                                         15
    •   at this time, Universe had cooled to 10 K
    •   electromagnetic & weak forces separated
          (small details about)   The Big Bang
                                     –38          –10
    Electroweak Era (10                    < t < 10     sec)

   This was experimentally verified in 1983:
    •   discovery of W & Z bosons
    •   electroweak particles predicted to exist above
           15
        10 K
And then something happens…
 From this high-energy state, galaxies and
  stars must eventually form
 What triggers galaxy formation?
 Why bubbles and voids?
 Why doesn’t the universe slow down as
  much as it should be?
 What is dark matter??
      The End of the Universe?
It is difficult beyond description to conceive
that space can have no end; but it is more
difficult to conceive an end. It is difficult
beyond the power of man to conceive an
eternal duration of what we call time; but
it is more impossible to conceive a time
when there shall be no time.
  Thomas Paine (1737 – 1809)
  American patriot, from “The Age of Reason”
               What is Dark Matter?
•   Recall rotation curve of
    Milky Way Galaxy.

    •   Clouds of H beyond our
        Sun orbit faster than
        predicted by Kepler’s Law

    •   But most of Galaxy’s light
        comes from stars closer to
        center than the Sun
               What is Dark Matter?
   There are only two
    possible explanations:
    •   we do not understand
        gravity on galaxy-size
        scales
    •   Higher velocities of
        Hydrogen gas are caused
        by gravitational attraction
        of unseen matter…called
        dark matter
            What is Dark Matter?
   IF we trust our theory of gravity...
       there may be 10 times more dark than
        luminous matter in our Galaxy

       luminous matter is confined to the disk

       dark matter is found in the halo and far
        beyond the luminous disk
        And still more Dark Matter!
   In other galaxies, we ―see‖ the same
    phenomena
       Rotation Curves of Spirals
   In clusters of galaxies, too
     Measuring Motions of galaxies
     Measuring ―Temperature‖ of gas
     Gravitational Lensing
        Velocities in Clusters of Galaxies
•   Pioneered by Fritz Zwicky.
    •   assume galaxies orbit about center
    •   measure orbital velocities measure
        each galaxy’s distance from center
    •   apply Kepler’s Law to calculate mass
   Zwicky found clusters had to
    be MUCH more massive!.
    •   his proposals of dark matter
        were met with skepticism in the
        1930s
    Measuring Motions in Clusters
•   Measuring galaxy orbits
    is not straightforward.
    •   we can only measure
        radial velocity
    •   must average all radial
        velocities to get the
        cosmological redshift
        (CR)
    •   subtract CR from each
        velocity
Intergalactic Gas Temperatures
Intracluster Medium contains hot (107–108
K) gas between galaxies emiting X-rays
 •   from X-ray spectrum, we can calculate the
     temperature
 •   gives average speed of gas particles
 •   again, we can estimate mass
       Gravitational Lensing
                      •   This is a gravitational
                          lens.
                      •   Einstein’s Theory of
                          Relativity states that
                          massive objects distort
                          spacetime.

•a massive cluster will bend the path of light which
approaches it (like a lens)
•the blue arcs are the lensed images of a galaxy which is
behind the cluster
        Agreement between methods

•   The cluster masses which are measured
    by all three of these independent
    methods agree:
    •   Most galaxy clusters must contain greater
        than 100 time the mass/light ration of one
        star like the sun.
    •   galaxy clusters contain far more mass in
        dark matter than in stars
        The Geometry of Space
   Space (and Time!) can take the shape of
     An infinitely expanding volume, accelerating
      over time
     A volume that gets bigger, but slows down to
      an eventual stop in an infinite amount of time
     A volume that reaches a maximum size, then
      recollapses
        The Geometry of Space
   Space (and Time!) can take the shape of
     An infinitely expanding volume, accelerating
      over time (OPEN)
     A volume that gets bigger, but slows down to
      an eventual stop in an infinite amount of time
      (FLAT)
     A volume that reaches a maximum size, then
      recollapses (CLOSED)
The Shape(s) of Space
A problem on the horizon?
           Dark Energy ?!?#%
   If the universe is really larger than it
    should be…
     Something must be making it expand…
     Energy must be present
     But we can’t see its source:



    Dark Energy!
Evidence for an Accelerating
        Universe?
    Four Models for the Future of the
               Universe
   Recollapsing Universe: the expansion will
    someday halt and reverse
   Critical Universe: will not collapse, but will
    expand more slowly with time
   Coasting Universe: will expand forever with
    little slowdown
   Accelerating Universe: the expansion will
    accelerate with time (currently ―favored‖)
              The critical density!
   How can we tell what the future holds?

       The amount of mass in the volume of space
        controls gravitational force’s impact

       Estimating ―critical density‖ is key!
              The Critical Density
•   IF gravitational attraction between galaxies
    can overcome the expansion of the Universe
    in localized regions.
    •   how strong must gravity be to stop the entire
        Universe from expanding?

    •   it depends on the total mass density of the
        Universe
            The Critical Density
•   if mass < critical density, the Universe will
    expand forever

•   if mass > critical density, the Universe will
    stop expanding and then contract

   The value of Ho tells us the current kinetic
    energy of the Universe AND indicates the
    critical density is 10–29 g / cm3
           The Critical Density
•   BUT all the luminous matter that we observe
    accounts for < 1% of critical density

•   And for dark matter to stop Universal
    expansion, even more would be required…

   This line of research suggests the Universe
    will expand forever!
Summary of Key Ideas
                   The Big Bang
   Astronomers believe that the universe began as an
    exceedingly dense cosmic singularity that expanded
    explosively in an event called the Big Bang. The Hubble
    law describes the ongoing expansion of the universe and
    the rate at which superclusters of galaxies move apart.
   The observable universe extends about 13.7 billion light-
    years in every direction from Earth to what is called the
    cosmic light horizon. We cannot see any objects that
    may exist beyond the cosmic light horizon because light
    from these objects has not had enough time to reach us.
                     The Big Bang
   According to the theory of inflation, early in its existence,
    the universe expanded super rapidly for a short period,
    spreading matter that was originally near our location
    throughout a volume of the universe so large that we
    cannot yet observe much of it. The observable universe
    today is thus a growing volume of space containing
    matter and radiation that was in close contact with our
    matter and radiation during the first instant after the Big
    Bang. This explains the isotropic and homogeneous
    appearance of the universe.
      A Brief History of Spacetime, Matter,
             Energy, and Everything
   Four basic forces—gravity, electromagnetism, the strong
    nuclear force, and the weak nuclear force— explain the
    interactions observed in the universe.
   According to current theory, all four forces were identical
    just after the Big Bang. At the end of the Planck time
    (about 10-43 s after the Big Bang), gravity became a
    separate force. A short time later, the strong nuclear force
    became a distinct force. A final separation created the
    electromagnetic force and the weak nuclear force.
   Before the Planck time, the universe was so dense that
    known laws of physics do not describe the behavior of
    spacetime, matter, and energy.
      A Brief History of Spacetime, Matter,
             Energy, and Everything
   In its first 30,000 years, the universe was radiation
    dominated, during which time photons prevented matter
    from forming clumps. Then it was matter-dominated, during
    which time superclusters and smaller clumps of matter
    formed. Today it is dark-energy-dominated. Dark energy of
    some sort supplies a repulsive gravitational force that
    causes superclusters to accelerate away from each other.
   Astronomers think that during the first 379,000 years of the
    universe, matter and energy formed an opaque plasma,
    called the primordial fireball. Cosmic microwave
    background radiation is the greatly redshifted remnant of
    the universe as it existed about 379,000 years after the Big
    Bang.
     A Brief History of Spacetime, Matter,
            Energy, and Everything
   By 379,000 years after the Big Bang, spacetime
    expansion caused the temperature of the universe to fall
    below 3000 K, enabling protons and electrons to
    combine to form hydrogen atoms. This event is called
    the era of recombination. The universe became
    transparent during the era of recombination, meaning
    that the microwave background radiation contains the
    oldest photons in the universe.
     A Brief History of Spacetime, Matter,
            Energy, and Everything
   Clusters of galaxies and individual galaxies formed from
    pieces of enormous hydrogen and helium clouds, each
    of which became a separate supercluster of galaxies.
   All of the superclusters and some of the clusters of
    galaxies within each supercluster are moving away from
    one another.
   During the matter-dominated era, structure formed in the
    universe. As the universe goes farther into the dark
    energy-dominated era, the large-scale structure of
    superclusters of galaxies will fade away.
               The Fate of the Universe
   The average density of matter and dark energy in the
    universe determines the curvature of space and the
    ultimate fate of the universe.
   Observations show that the universe is flat and that the
    cosmic microwave background is almost perfectly isotropic,
    resulting from a brief period of very rapid expansion (the
    inflationary epoch) in the very early universe.
   The universe is accelerating outward and it will expand
    forever.
                 Key Terms
Big Bang                      isotropy
closed universe               isotropy problem
confinement                   matter-dominated universe
cosmic light horizon          open universe
cosmic microwave background   pair production
cosmological constant         Planck time
cosmological redshift         primordial fireball
cosmology                     primordial nucleosynthesis
dark ages                     quark
dark energy                   quintessence
decoupling                    radiation-dominated universe
era of recombination          strong nuclear force
expanding universe            superstring theories
Grand Unified Theory (GUT)    Theories of Everything
homogeneity                   universe
horizon problem               weak nuclear force
inflation
inflationary epoch
    WHAT DID YOU THINK?
 What is the universe?
 It is all of the matter, energy, and
  spacetime that will ever be detectable from
  Earth or that will ever affect us.
     WHAT DID YOU THINK?
 Did the universe have a beginning?
 Yes, it occurred about 13.7 billion years
  ago, in an event called the Big Bang.
     WHAT DID YOU THINK?
 Into what is the universe expanding?
 Nothing. The Big Bang created space and
  time (spacetime), as well as all matter and
  energy in the universe. Spacetime is
  expanding to accommodate the expansion
  of the universe.
    WHAT DID YOU THINK?
 How strong is gravity compared to the
  other forces in nature?
 Gravity is by far the weakest force.
    WHAT DID YOU THINK?
 Will the universe last forever?
 Current observations support the belief
  that the universe will last forever.