Section 30.3
Cosmology
Objectives
Distinguish the different models of the universe.
Compare and contrast how expansion is
relative to each of the models.
Explain the importance of the Hubble constant.
Section 30.3
Cosmology
The Big Bang theory was formulated by
comparing evidence and models to describe
the beginning of the universe.
Review Vocabulary
radiation: the process of emitting radiant
energy in the form of waves or particles
Section 30.3
Cosmology
New Vocabulary
cosmology
Big Bang theory
cosmic background
radiation
Section 30.3
Cosmology
Big Bang Model
The study of the universe—its nature, origin,
and evolution—is called cosmology.
The theory that the universe began as a
point and has been expanding since is the
Big Bang theory.
Section 30.3
Cosmology
Big Bang Model
Outward expansion
When the rate of expansion( H- Hubble
constant) of the universe is known, it is
possible to calculate the time since the
expansion started and determine the age of
the universe.
Section 30.3
Cosmology
Big Bang Model
Outward expansion
Based on the best value for H that has been
calculated from Hubble Space Telescope
data and the data on the cosmic background
radiation, the age of the universe can be
pinpointed to 13.7 billion years.
Section 30.3
Cosmology
Big Bang Model
Outward expansion
In the Big Bang model, the
momentum of the outward
expansion of the universe is
opposed by the inward force
of gravity acting on the
matter of the universe to
slow that expansion.
Section 30.3
Cosmology
Big Bang Model
Possible outcomes
Based on the Big Bang theory,
there are three possible
outcomes for the universe.
1.The universe could be an
open universe and continues
to expand forever. (expansion
greater than gravity.)
Open universe
Section 30.3
Cosmology
Big Bang Model
2.The universe could be a
closed universe where the
expansion stops and all of the
mass is pulled back to the
original point of origin,(Gravity is
greater)
3. it could be a flat universe
where the expansion becomes
so slow that it seems to stop.
(expansion almost equal to
gravity)
Closed universe
Flat universe
Section 30.3
Cosmology
Big Bang Model
Critical density
All three outcomes are based on the premise
that the rate of expansion has slowed since
the beginning of the universe, but the
density of the universe is what is
unknown.
Section 30.3
Cosmology
Big Bang Model
Critical density
At the critical density, there is a balance, so
that the expansion will come to a halt in an
infinite amount of time. The critical density,
about 6 × 10–27 kg/m3, means that, on average,
there are only two hydrogen atoms for every
cubic meter of space.
Section 30.3
Cosmology
Cosmic Background Radiation
Discovery
In 1965, scientists discovered a persistent
background noise in their radio antenna. This
noise was caused by weak radiation, called
the cosmic background radiation, that
appeared to come from all directions of space
and corresponded to an emitting object having
a temperature of about 2.735 K (–270C).
Section 30.3
Cosmology
Cosmic Background Radiation
Discovery
The temperature was very close to the
temperature predicted by the Big Bang
theory, and the radiation was interpreted
to be from the beginning of the Big Bang.
Section 30.3
Cosmology
Cosmic Background Radiation
Mapping the radiation
Earth’s atmosphere blocks much of the
cosmic background radiation, so it is best
observed from high-altitude balloons or
satellites. An orbiting observatory called the
Wilkinson Microwave Anisotropy Probe
(WMAP), launched by NASA in 2001,
mapped the radiation in greater detail.
Section 30.3
Cosmology
Cosmic Background Radiation
Mapping the radiation
The peak of the radiation measured by WMAP
has a wavelength of approximately 1 mm;
thus, it is microwave radiation in the radio
portion of the electromagnetic spectrum.
Section 30.3
Cosmology
Cosmic Background Radiation
Acceleration of the expansion
The data produced by WMAP have provided
enough detail to refine cosmological models. In
particular, astronomers have found small wiggles
in the radiation representing the first major
structures in the universe. This helped to pinpoint
the time at which the first galaxies and clusters of
galaxies formed and also the age of the universe.
Section 30.3
Cosmology
Cosmic Background Radiation
Acceleration of the expansion
According to every standard model, the
expansion of the universe is slowing down
due to gravity. However, there was a
surprising discovery that the expansion of
the universe is now accelerating.
Astronomers have labeled this acceleration
dark energy.
Section 30.3
Cosmology
Contents of the Universe
Dark matter and energy
Universe is composed of dark matter (21
percent), dark energy (75 percent), and
luminous matter (4%).
What is unknown today is the nature of
the dark matter and dark energy.
Section 30.3
Cosmology
Contents of the Universe
Dark matter and energy
Dark matter is thought to consist of subatomic
particles, but of the known particles, none
display the right properties to explain or fully
define dark matter.
Although scientists recognize the effects of
dark energy, they still do not know what it is.
CH
Study Guide
Key Concepts
Section 30.3 Cosmology
The Big Bang theory was
formulated by comparing evidence and models
to describe the beginning of the universe.
 The study of the universe’s origin, nature, and
evolution is cosmology.
 The Big Bang model of the universe came
from observations of density and acceleration.
CH
Study Guide
Key Concepts
Section 30.3 Cosmology
 The critical density and the amount of dark
energy of the universe will determine
whether the universe is open or closed.
 Cosmic background radiation gives support
to the Big Bang theory of the universe.
 Mapping the cosmic background radiation
has indicated the existence of dark matter
and dark energy.
CH
Galaxies and the Universe
30.3 Section Questions
Cosmologists estimate that the universe
is composed mostly of dark matter and
dark energy.
a. true
b. false
CH
Galaxies and the Universe
30.3 Section Questions
Cosmologists have observed that the expansion
of the universe is accelerating. What may be the
cause of this acceleration?
a. dark matter
b. dark energy
c. Big Bang momentum
d. gravity
CH
Galaxies and the Universe
30.3 Section Questions
What is the cosmic background radiation?
Answer: Cosmic background radiation—a
persistent background noise that is picked up
by radio antenna—is leftover radiation from
the early, hot phase of the universe’s
expansion, also known as the Big Bang.
CH
Galaxies and the Universe
Chapter Assessment
Questions
The diagram shows a side view of the Milky
Way galaxy. Where are the oldest stars in the
galaxy likely to be found?
a. spiral arms
b. outer disk
c. inner disk
d. nuclear bulge
CH
Galaxies and the Universe
Chapter Assessment
Questions
There are several hypotheses about why
galaxies keep their spiral shape. What does
one hypothesis say is responsible for creating
a galaxy’s spiral arms?
a. spiral energy waves
b. spiral halo waves
c. spiral density waves
d. spiral disk waves
CH
Galaxies and the Universe
Chapter Assessment
Questions
What could be defined as the velocity at which
a galaxy is moving away from Earth, divided
by its distance from Earth?
Answer: the Hubble constant
CH
Galaxies and the Universe
Chapter Assessment
Questions
What are active galactic nuclei?
Answer: Active galactic nuclei are the cores
of galaxies that emit exceedingly large
amounts of energy from their centers.
CH
Galaxies and the Universe
Chapter Assessment
Questions
How might active galactic nuclei and quasars
be related?
Answer: Today’s active galactic nuclei might
be former quasars that are not as energetic as
they were billions of years ago.
CH
Galaxies and the Universe
Standardized Test
Practice
In which part of a spiral galaxy are new stars
being formed?
a. spiral arms
b. central bulge
c. halo
d. globular clusters
CH
Galaxies and the Universe
Standardized Test
Practice
What occupies the centers of most galaxies?
a. quasars
b. density waves
c. superclusters
d. black holes
CH
Galaxies and the Universe
Standardized Test
Practice
In which part of the Milky Way galaxy is our solar
system located?
a. a spiral arm
b. the central bulge
c. the halo
d. a globular cluster
CH
Galaxies and the Universe
Standardized Test
Practice
What is a radio galaxy?
Answer: A radio galaxy is one that emits as
much or more energy in radio wavelengths
than it does in wavelengths of visible light.
CH
Galaxies and the Universe
Standardized Test
Practice
How have cosmologists used galactic clusters
to infer the existence of dark matter?
Answer: The total mass of the galaxies in the
cluster is determined by the motions of the
galaxies. That sum is much greater than the
mass that can be determined by the galaxies’
luminosity. The difference in mass is evidence
of the existence of dark matter.