Astronomy 182: The Origin and Evolution of the Universe

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Astronomy 182 The Origin and Evolution of the
Universe
Lecture 2


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Astronomy 182 The Origin and Evolution of the
UniverseCourse information
Class meets Tuesdays, Thursdays 130-250 in AAC
107 Prof. Josh Frieman (frieman_at_oddjob.uchicago.e
du) Tel [phone] (Tu/Th) 630-840-2226
(MWF) Office hours AAC 032 after class or by
appt. Grader Dave Johnston
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References Texts
Textbooks T. Ferris, The Whole Shebang
(Touchstone Books 1997) B. Greene, The Elegant
Universe (Vintage, 1999) References A. Guth and
A. Lightman, The Inflationary Universe J. Silk,
A Short History of the Universe C. Hogan, The
Little Book of the Big Bang More advanced A.
Liddle, An Introduction to Modern Cosmology E.
Linder, First Principles of Cosmology A request
has gone in to Crerar Library to place all of
these on reserve.

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Class Website

• Printable Course outline/syllabus
• Lecture schedule and electronic versions of
  Lectures
• Textbooks and references
• Links to other cosmology sites (in progress send
  links!)
• URL
• http//astro.uchicago.edu/frieman/A182/
• At the moment, the Lectures can only be viewed
  with
• a Microsoft Internet Explorer browser
  working on it

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Assignment
For next week Read Preface, Chapters 1 and 2 of
T. Ferris, The Whole Shebang (Touchstone Books
1997) For April 9 Hand in first 3-page essay
summarizing your understanding of Ferris,
Chapter 2, along with 1 page of questions on
issues you do not understand or feel were not
presented clearly in the book or in class. Start
surfing the web for cosmology sites.

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Today
--Finish Overview of the Course --Brief History
of pre-Modern Cosmology --Expansion of
the Universe, Part I
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The Big Bang Theorya well-tested framework for
understanding the observationsand for asking new
questions
The Universe has been expanding isotropically
from a hot, dense beginning (aka the Big Bang)
for about 13 billion years The only successful
framework we have for explaining several key
facts about the Universe ?Hubbles law of
galaxy recessionexpansion ?Uniformity
(isotropy) of Microwave background ?Cosmic
abundances of the light elements
Hydrogen, Helium, Deuterium, Lithium, cooked in
the first 3 minutes

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The Big Bang Theory
Not just a theory, but one of the most firmly
established paradigms in science.
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The Big Bang Theory
Not just a theory, but one of the most firmly
established paradigms in science. One of our
goals in this course will be to establish the
bases for this statement.
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The Big Bang Theory
Not just a theory, but one of the most firmly
established paradigms in science. One of our
goals in this course will be to establish the
bases for this statement. At the same time, the
Big Bang is an idealization, a simplified descript
ion (analogous to the approximation of the Earth
as a perfect sphere), and cosmologists are now
occupied with mapping out/filling in the
details. Even so, certain basic elements of the
model remain to be understood e.g., the Natures
of the Dark Matter Dark Energy which together
make up 95 of the mass-energy of the Universe
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The Big Bang Theory
The Big Bang is an idealization, a
simplified description (analogous to the
approximation of the Earth as a perfect sphere),
and cosmologists are now occupied with mapping
out/filling in the details. Even so, certain
basic elements of the model remain to be
understood e.g., the natures of the Dark Matter
Dark Energy which together make up 95 of the
mass-energy of the Universe These puzzles do
NOT mean that the Big Bang Theory is
wrongrather, it provides the framework for
investigating them.
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The Big Bang Theory
Imperfect analogy with Darwins Theory of
Evolution Evolution was well established by
data (fossil record) well before its
molecular-genetic basis in DNA was found. It
provides a broad framework for understanding the
more recent biological developments. Galaxy
Surveys ?? Human Genome
Project mapping the
mapping the genome Universe Key
difference cosmologists have a successful theory
for the formation of the hierarchical
structures (galaxies, clusters, large-scale
structure) seen in the Universe
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Einstein and General Relativity
Idea Matter affects the structure of
Space-Time
A massive star attracts nearby objects by
distorting spacetime
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Einstein space can also be globally curved
What is the geometry of three-dimensional space?
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Einstein space can also be globally curved
What is the geometry of space? Recent
observations of the Microwave background
radiation indicate it is flat
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The Future of the Universe
Newton Einstein the expansion of the Universe
should be slowing down over time, due to the
mutual gravitational attraction of all
matter in the Universe If there is enough matter
in the Universe, we would expect the
expansion to eventually halt, and the Universe
to recollapse in a big crunch. If there is too
little matter, we expect the Universe will
continue to expand forever. Which of these
Universes do we inhabit?
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Accelerating
Empty
Size of the Universe
Open
Closed
Will the Universe expand forever or recollapse in
a Big Crunch?
Today
Cosmic Time
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Distant Supernova Explosions indicate that the
Expansion of the Universe is Accelerating rathe
r than Slowing Down Unexpected and
quite Interesting
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What is causing the acceleration of the
Universe? Dark Energy a new form of energy
permeating the Universe What are its
properties? Will the acceleration continue
into the indefinite future?
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The Early Universethe key to Large-scale
Structure
From our vantage point 13-14 billion years after
the Big Bang, we are now trying to unravel what
happened in the earliest tiny fraction of a
second, when the Universe was 10-35
seconds (0.000000000000000000000000000000000001
seconds) old! We can test our ideas about the
Very Early Universe by observing the
distributions of galaxies and of cosmic
radiations (e.g., the Microwave background) in
space. This has been a major breakthrough in
cosmology over the last decade.
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Early
Evolution of Structure in a Simulated Big
Bang Universe Filled with Dark Matter The
Cosmic Web Galaxies and Clusters form at the
intersections of sheets and filaments, very
similar to the Structure seen in galaxy surveys
Today
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Early SDSS Data 200,000 Galaxies Mapped in
3D so far
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The Big Bang TheoryHow do we really know its
correct?
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The Big Bang as Cultural Metaphor
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From The New Yorker, March 5, 2001 A hiss of
chronic corruption suffuses the capital like
background radiation from the big bang.
--Hendrik
Hertzberg
The Talk of the Town
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(as seen on public buses and roadside billboards)
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Cosmology vs. Religion?
There should be a mutually enriching conversation
between science and religion about the
implications of new discoveries about the
Universe, and an understanding of the nature
and limitations of science. Creationism (or
Creation Science, or Arguments from Design)
is not a rational, scientific alternative to Big
Bang cosmology (or evolution), any more than
the Flat Earth theory is a plausible
alternative to modern geography. An old
antagonism based on misunderstanding Cf.
Galileo, Bruno,
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Cosmology vs. Religion?

• Why should responsible citizens should be
  informed about these matters?
• State textbook committees in Kansas (late 1990s)
  
• and Ohio (currently) have debated removal
  of
• evolution and the Big Bang from school
  curricula
• or giving equal time to creationist
  alternatives
• The U.S. government spends many millions
• annually on cosmology research your tax
  dollars
• at work.

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224?Youve got to be kidding. --God
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While the Big Bang Theory does not rest on as
firm a ground as arithmetic, it springs from
the same principles. It is a well-tested
framework that we use to understand the
evolution of the Universe on the largest scales.
If a better idea than the Big Bang were to come
along, cosmologists would not hesitate to
abandon it while science is perhaps
inherently conservative (Cf. T. Kuhn, The
Structure of Scientific Revolutions), it is also
highly competitive and subject to trends and
fashions--if a hot new idea comes along, few
of us can resist the temptation to explore
it. But it must be at least as successful as the
current paradigm and in addition show promise
of explaining the previously unexplained
or of unifying previously disparate strands
of thought.

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Some Key Questions for 21st Century Cosmology
How did the hierarchy of large-scale structure,
from stars to galaxies to clusters and beyond,
form? Did this structure arise from the
expansion stretching of microscopic quantum
ripples in the fabric of spacetime during the
earliest moments of the Big Bang (a theory known
as cosmic Inflation)? What is the nature of the
Dark Matter that makes up most of the mass of the
Universe? Is it in the form of exotic elementary
particles as yet undiscovered? (The Ultimate
Copernican Principle) What is the nature of the
Dark Energy that is causing the expansion of the
Universe to Accelerate? Will the Universe
continue to accelerate forever? What happened
before the Big Bang? Is this question
meaningful? Are there more than 3 spatial
dimensions? Can we ever detect them?

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Despite major recent advances in cosmology, such
fundamental mysteries remain
Unlike the ancient mystics, however, we hope
these unexplained phenomena can in principle be
understood, by a combination of new theoretical
insight and experimental advances scientists are
perpetual optimists. So far, this optimism has
been justified by the continued progress of
science. What are the ultimate limits to our
understanding of the Universe?

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History the Universe in Time Space
Creation Myths (e.g., Enuma Elish) 1.
Describe birth of Universe in terms of the
observed environment, extrapolating observed
processes of change 2. Universe begins in
time--it is dynamic, changing. Late Greek era
through 1920s Universe is static and
everlasting.
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Pre-Socratic debate Heraclitus change is
fundamental to the world Parmenides
change is an illusion. Reality is
essentially static. The
One. Aristotle (5th cent. BC)On the Heavens
The Universe began in time, but is
thereafter unchanging and everlasting
into the future. Aristotelian view of a
static Universe dominated scientific discourse
well into the 20th Cent.
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Einstein Theory of General Relativity (GR)
(1916) According to equations of GR,
Universe is time-dependent (dynamic)
since this conflicted with prevailing assumption
of a static Universe, he added a term to
his equations, the Cosmological Constant,
in order to get static solutions. After the
expansion of the Universe was discovered in
late 1920s, he called this the biggest
blunder of my life (since he could have
predicted the Expanding Universe). Friedmann
(1922) had earlier showed that Einsteins theory
contains expanding and contracting
Universe solutions. (Also Lemaitre, de
Sitter, Robertson, and Walker,) Einstein
initially criticized this work, but later
accepted it. In fact, Einsteins static
Universe solutions are unstable they
eventually contract or expand. But his
Cosmological Constant has recently been
revived for completely different reasons!
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The Universe in Space
An Infinite Universe Greek atomists
(Democritus), Chinese cosmologists of
the Hsuan Yeh school. Plato the material world
is finite but surrounded by an infinite
void. Archytas (friend of Plato) (and later
Lucretius, 60 BC) If I am at the
extremity of the heaven of stars, can I not
stretch outward my hand? It is absurd to
suppose I could not if I can, what is
outside must be either body or space. i.e.,
the material world must be infinite
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Aristotle Universe is finite (concentric
crystalline spheres centered on the
Earth) Again, Aristotelian view prevailed and
became dogma. Giordano Bruno burned at the stake
(1600) for heretical views, including
espousing that the Universe is infinite. H.
Curtis vs. H. Shapley Great Debate (1920) on
the Scale of the Universe
Controversy over the distances and nature of the
spiral nebulae part of our Galaxy
(Shapley) or separate galaxies
(island universes, Cf. Kant) Issue settled in
1923 by E. Hubble, who resolved stars in
a number of spiral nebulae (and later measured
their distances)
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M87 Nebula in Orion (star forming region in our
galaxy)
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NGC 1087 spiral galaxy in Aries
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Hubbles Law and the Expanding Universe
Slipher (1922) measured redshifts (recession
velocities) of 40 spiral galaxies by their
spectra Doppler effect Henrietta Leavitt
studied Cepheid variable stars in our
Galaxy, showed a correlation between their
Luminosity and their Period of variation
L(T) Hubble (1929)found Cepheids in 20 nearby
galaxies and measured their periods T ?
inferred L. From their apparent brightness
(flux f L/4pd2), he then obtained their
distances d. Comparing the distances d with
Sliphers radial velocities v, he
empirically found that vHd
where H550 km/sec/Megaparsec

Hubbles constant
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Distances and Units
1 parsec (pc) 3.26 light years (parallax of
1 arcsecond) 1 light year (3x1010 cm/sec) x (1
yr3x107 sec) 9.4x1017 cm 1
kiloparsec (kpc) 103 pc (10 kpc typical
galaxy size) 1 Megaparsec (Mpc) 106 pc
typical distance between
neighboring
galaxies Our Sun is approximately 8.5 kpc from
the center of the Milky Way Galaxy Andromeda
galaxy is about 700 kpc from the Milky Way
(nearest large galaxy, companion to the Milky Way)
speed of light c
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Edwin P. Hubble (1884-1953) (U of C graduate)
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The Redshift Measuring radial
velocities via Doppler-shifted emission and
absorption lines in the spectra from gas and
stars These are easy to measure accurately.
Measuring distances much more difficult.
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D
D
D distance travelled by light wave in time Dt
Stationary Source emitting light waves at
intervals (Dt)
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D
D
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D
d
Moving source emitting light waves at intervals Dt
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D
D
l
l distance between successive wavecrests in
direction of motion D c (Dt) v (Dt)
(c-v)(Dt)
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?
l l
Note Dt is same thing as ?t
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Doppler Shift of Light Wavelength
Wavelength ? distance between successive crests
Observed wavelength ? Rest wavelength ?0
Wavelength of light (or sound) emitted by moving
object is shortened if it is approaching you,
lengthened if it recedes from you
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Light wavelength corresponds to color blue
short
red long
Light from a receding source is shifted to the
red redshift
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Electromagnetic Wavelength Spectrum
Increasing wavelength
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Hydrogen emission and absorption lines
Atomic Energy Levels
Downward (upward) transition between two energy
levels of an atom accompanied by emission
(absorption) of light ?E energy
difference between the levels it determines
wavelength of emitted or absorbed light
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Spectroscopy of Stars and Galaxies
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Galaxy Spectrum
Emission lines
Absorption lines
(Angstroms)
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Redshifting of Galaxy Emission Lines v/c z
??/?0 (approximation for objects moving with
v/c ltlt 1)
receding slowly
?
receding quickly
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Hubbles data (1929) H v/d 500
km/sec/Megaparsec
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Hubble Space Telescope 1990s
Measuring distances using Cepheid variable stars
same method as Shapley/Hubble, but 10 times
farther and also more accurate
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Hubble Space Telescope
Modern value H0 72 /- 7 km/sec/Mpc
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Next Time Interpretation of Hubbles Law in
terms of the Expanding Universe