1. Chapter 18: Cosmology
For a humorous approach to quarks, check out the Jefferson Lab’s game.  In Looking for the Top Quark, each player receives six quarks that they hide on a grid. The players use coordinates to find their opponent's hidden quarks. The first player to find all six of their opponent's quarks wins!   education.jlab.org/topquarkgame/
Information on the Planck mission will be found at

2. WHAT DO YOU THINK? What does the Universe include?
Did the Universe have a beginning?
Is the Universe expanding, fixed in size, or contracting?
Will the Universe last forever?

3. You will discover…
Cosmology, which seeks to explain how the Universe began, how it evolves, and its fate.
The best theory we have for the evolution of the Universe – the Big Bang.
How astronomers explain the overall structure of the Universe.
Our understanding of the fate of the Universe.

4. In the Beginning – the Big Bang
The Universe began 13.7 billion years ago with an event called the “Big Bang.”
All of space-time, matter, and energy were created at the Big Bang.
The left-over energy from the Big Bang can be detected today as the Cosmic Microwave Background Radiation.
The temperature of this radiation is only a few degrees above absolute zero.

5. The Beginning – The Big Bang

6. In Search of The Earliest Photons
FIGURE 18-3 In Search of Primordial Photons (a) The
Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched
in 2001, improved upon the measurements of the spectrum and
angular distribution of the cosmic microwave background taken
by the COBE satellite. (b) The balloon-carried telescope
BOOMERANG orbited above Antarctica for 10 days collecting data
used to resolve the cosmic microwave background with 10 times
higher resolution than that of COBE. All these experiments found
local temperature variations across the sky, but no overall
deviation from a perfect blackbody spectrum. (a: NASA/WMAP
Science Team b: The BOOMERANG Group, University of California, Santa
Barbara)
Wilkinson Microwave Anisotropy Probe (WMAP) satellite, launched in 2001

7. WMAP’s Baby Picture of the Universe – Cosmic Microwave Background Radiation

8. The Universe is Expanding
The Redshift of Superclusters shows us that the Universe is expanding. This Redshift is called the “Cosmological Redshift,” because it is caused by the expansion of space.
The farther away a galaxy is from us, the faster it moves away from us.

9. The Expansion of the Universe – Cosmological Redshift
FIGURE 18-1 Cosmological Redshift Just as the waves drawn
on this rubber band are stretched along with the rubber band,
so too are the wavelengths of photons stretched as the universe
expands.
Space itself is expanding.

10. Expanding Cake Analogy
The Expanding Chocolate Chip Cake
Analogy The expanding universe can be
compared to a chocolate chip cake baking
and expanding in the Space Shuttle’s microwave oven. Just
as all the chocolate chips move apart as
the cake rises, all the superclusters of
galaxies recede from each other as the
universe expands.
Just as all the chocolate chips move apart as the cake rises, all the superclusters of galaxies move away from each other as the space of the Universe expands.

11. The Observable Universe
FIGURE The Observable Universe
This diagram shows why we only see part
of the entire universe. As time passes, this
volume grows, meaning that light from
more distant galaxies reaches us. The
galaxies we see at the farthest reaches of
our telescopes’ resolving power are as they
were within a few hundred million years
after the Big Bang (see inset). These
galaxies, formed at the same time as the
Milky Way, appear young because the light
from their beginnings is just now reaching
us. The radius of the cosmic light horizon is
equal to the distance that light has traveled
since the Big Bang. Because the Big Bang
occurred about 13.8 billion years ago,
the cosmic light horizon today is about
13.8 billion light-years away in all directions.
Inset: This image of the Hubble Deep Field
shows some of the most distant galaxies
we have seen. (inset: Robert Williams and the
Hubble Deep Field Team, STScI and NASA)
The cosmic light horizon today is about 13.7 billion light-years away in all directions.

12. HST – Galaxies >13 Billion LY Away
This HST Ultra Deep Field Telescope image shows some of the most distant galaxies we have seen.
FIGURE Distant Galaxies (a) The young cluster of
galaxies MS , shown on the left, contains many orbiting
pairs of galaxies, as well as remnants of recent galaxy collisions.
Several of these systems are shown at the right. This cluster is
located 8 billion light-years away from Earth. (b) This image of
more than 300 spiral, elliptical, and irregular galaxies contains
several that are an estimated 12 billion light-years from Earth.
Two of the most distant galaxies are shown in the images on the
right, colored in red at the centers of the pictures. (a, b: P. Van
Dokkum, Uner of Granengen, ESA and NASA)

13. Early Universe Temperature Variations
FIGURE Structure of the
Early Universe This microwave
map of the entire sky, produced
from data taken by the Wilkinson
Microwave Anisotropy Probe
(WMAP), shows temperature
variations in the cosmic microwave
background. Red regions are about
K warmer than the
average temperature of 2.73 K; blue
regions are about K cooler
than the average. Inset: These tiny
temperature fluctuations, observed
by BOOMERANG, are related to the
large-scale structure of the
universe today, indicating where
superclusters and voids grew. The
radiation detected to make this map
is from a time 379,000 years after
the Big Bang. (NASA/WMAP Science
Team; inset: NSF/NASA)
Tiny temperature fluctuations in the Cosmic Microwave Background Radiation are related to the large-scale structure of the Universe today, indicating where Superclusters and voids grew.

14. The First Stars – much larger than the Sun – with much shorter lives
FIGURE Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the burst of
star formation that occurred within a few hundred million years
after the Big Bang. The arcs and irregular circles represent
interstellar gas that is illuminated by supernovae. (b) Using the
Hubble and Keck telescopes, astronomers discovered two groups of
stars (arrows) 13.4 Bly away that are believed to be protogalaxies,
from which bigger galaxies grew. These protogalaxies were
discovered because they were enlarged by the gravitational lensing
of an intervening cluster of galaxies. (c) The Chandra X-ray
telescope imaged gravitationally bound gas around the distant
galaxy 3C 294. The X-ray emission from this gas is the signature of
an extremely massive cluster of galaxies, in this case at a distance
of about 11.2 Bly from us. (a: Adolf Schaller, STScI/NASA/K. Lanzetta,
SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib (Observatorie Midi-
Pyrenees, France), NASA, ESA; c: NASA)
The burst of star formation that occurred within a few hundred million years after the Big Bang.

15. Proto-Galaxy Formation
FIGURE Galaxies Forming by Combining Smaller Units
(a) This painting indicates how astronomers visualize the burst of
star formation that occurred within a few hundred million years
after the Big Bang. The arcs and irregular circles represent
interstellar gas that is illuminated by supernovae. (b) Using the
Hubble and Keck telescopes, astronomers discovered two groups of
stars (arrows) 13.4 Bly away that are believed to be protogalaxies,
from which bigger galaxies grew. These protogalaxies were
discovered because they were enlarged by the gravitational lensing
of an intervening cluster of galaxies. (c) The Chandra X-ray
telescope imaged gravitationally bound gas around the distant
galaxy 3C 294. The X-ray emission from this gas is the signature of
an extremely massive cluster of galaxies, in this case at a distance
of about 11.2 Bly from us. (a: Adolf Schaller, STScI/NASA/K. Lanzetta,
SUNY; b: Richard Ellis (Caltech) and Jean-Paul Kneib (Observatorie Midi-
Pyrenees, France), NASA, ESA; c: NASA)
Hubble and Keck telescope images of two groups of stars that are believed to be proto-galaxies, from which bigger galaxies grew

16. Creation of Spiral and Elliptical Galaxies
If the rate of star formation was low, then a spiral galaxy formed.
If the rate of star formation was high, then an elliptical galaxy formed.
FIGURE The Creation of Spiral and
Elliptical Galaxies A galaxy begins as a huge
cloud of primordial gas that collapses
gravitationally. (a) If the rate of star birth is low,
then much of the gas collapses to form a disk,
and a spiral galaxy is created. (b) If the rate of
star birth is high, then the gas is converted into
stars before a disk can form, resulting in an
elliptical galaxy.
A galaxy begins as a huge cloud of primordial gas that collapses gravitationally.

17. The Fate of the Universe
The fate of the Universe depends on the shape of space-time.
The shape of space-time is determined by how much total matter and energy there is in the Universe.
Space-time could have one of three shapes:
Sphere = positive curvature = closed.
Our floor = no curvature = flat.
Saddle = negative curvature = open.

18. Possible Shapes of Space-time, and the Fate of the Universe
Closed – Universe would collapse.
Flat – Universe could slowly expand forever.
Open – Universe would expand forever.
FIGURE The Possible Geometries of the Universe The
shape of space (represented here as two-dimensional for ease of
visualization) is determined by the matter and energy contained in
the universe. The curvature is either (a) positive, (b) zero, or
(c) negative, depending on whether the average matter and energy
density throughout space is greater than, equal to, or less than a
critical value. The lines on each curve are initially parallel. They
converge, remain parallel, or diverge depending on the curvature
of space.

19. Cosmic Microwave Background indicates that Space-time is Flat – Universe could slowly expand forever
FIGURE The Cosmic Microwave
Background and the Curvature of Space
Temperature variations in the early universe
appear as “hot spots” in the cosmic
microwave background. The apparent sizes
of these spots depend on the curvature of
space. (a) In a closed universe with positive
curvature, light rays from opposite sides of
a hot spot bend toward each other. Hence,
the hot spot appears larger than it actually
is, as shown by the dashed lines. (b) The
light rays do not bend in a flat universe. (c)
In an open universe, light rays bend apart.
The dashed lines show that a hot spot
would appear smaller than its actual size.
(The BOOMERANG Group, University of
California, Santa Barbara)

20. BUT – dimmer distant Supernovae mean the expansion of the Universe is speeding up.
FIGURE Dimmer Distant Supernova
(a) These Hubble Space Telescope images show the
galaxy in which the supernova SN 1997ff occurred. This
supernova, more than 10 Bly away, was dimmer than
expected, indicating that the distance to it is greater
than the distance it would have if the universe had
been continually slowing down since the Big Bang. This
supports the notion that an outward (cosmological)
force is acting over vast distances in the universe. The
arrow on the first inset shows the galaxy in which the
supernova was discovered. The bright spot on the
second inset shows the supernova by subtracting the
constant light emitted by all the other nearby objects.
(b) The distances and brightnesses of many very
distant supernovae are plotted on this diagram. The
location of the most distant supernovae in the upper
region strongly indicates that the universe has been
accelerating outward for the past 6 billion years.
(a: Adam Riess, Space Telescope Science Institute, NASA)

21. 100 billion years from now the Universe will appear frozen in time as we look out into space. Only the light from the Local Group of galaxies will remain visible, if anyone is still around to see it.

22. Expansion of the Universe is speeding up
Very distant Type 1a Supernovae are not as bright as they should be.
This means the expansion of the Universe is speeding up instead of slowing down or staying the same.
There is something really weird called Dark Energy (not the same as Dark Matter) that is causing this acceleration.
Dark Energy acts like anti-gravity, pushing the Universe apart.
We do not know what this Dark Energy is, but it makes up 73% of the total energy/matter of the Universe.

23. Composition of the Universe
Suppose all the matter and energy in the Universe is $100 in your wallet or purse.
$73 would be Dark Energy – the mysterious energy that’s pushing the Universe apart faster and faster.
$23 would be Dark Matter – matter that doesn’t give off any kind of radiation, so we can’t see it – but it does have gravity.
So out of your Universe of $100, $96 represents Dark Energy and Dark Matter that have yet to be identified.
Only $4 would be visible matter – the regular stuff we can see, like stars, gas clouds, and dust – the same stuff we’re made of.
Of the visible matter ($4), only one-tenth of it shines as stars. That’s 40 cents out of your total $100. The rest of the visible matter is gas clouds and dust.

24. Composition of the Universe

25. WHAT DID YOU THINK? What does the Universe include?
It is all the matter, energy, and space-time that will ever be detectable from the Earth or that will ever affect us.
Did the Universe have a beginning?
Yes, it occurred about 13.7 billion years ago in an event called the Big Bang.
Is the Universe expanding, fixed in size, or contracting?
The Universe is expanding, faster and faster.
Will the Universe last forever?
Current observations support the belief that it will last (expand) forever.