Section 4: The Big Bang Theory

1
Section 4 The Big Bang Theory

• Preview
• Key Ideas
• Hubbles Observations
• A Theory Emerges
• Big Bang Theory
• Universal Expansion
• A Universe of Surprises
• Maps In Action

2
Key Ideas

• Explain how Hubbles discoveries lead to an
  understanding that the universe is expanding.
• Summarize the big bang theory.
• List evidence for the big bang theory.

3
Hubbles Observations

• cosmology the study of the origin, properties,
  processes, and evolution of the universe
• Cosmologists and astronomers can use the light
  given off by an entire galaxy to create the
  spectrum for that galaxy.
• Edwin Hubble used galactic spectra to uncover new
  information about our universe.

4
Hubbles Observations, continued

• Measuring Red Shifts
• Hubble found that the spectra of galaxies, except
  for the few closest to Earth, were shifted toward
  the red end of the spectrum.
• Hubble determined the speed at which the galaxies
  were moving away from Earth.
• Hubble found that the most distant galaxies
  showed the greatest red shift and thus were
  moving away from Earth the fastest.

5
Hubbles Observations, continued

• The Expanding Universe
• Using Hubbles observations, astronomers have
  been able to determine that the universe is
  expanding.
• The expanding universe can be thought of as a
  raisin cake rising in the oven. If you were able
  to sit on one raisin, you would see all the other
  raisins moving away from you.
• Similarly, galaxies in the universe are moving
  farther away from each other due to the expansion
  of the universe.

6
A Theory Emerges

• Although cosmologists have proposed several
  different theories to explain the expansion of
  the universe, the current and most widely
  accepted is the big bang theory.
• big bang theory the theory that all matter and
  energy in the universe was compressed into an
  extremely small volume that 3 to 15 billion years
  ago exploded and began expanding in all
  directions
• By the mid-20th century, almost all astronomers
  and cosmologists accepted the big bang theory.

7
A Theory Emerges, continued

• Reading Check
• What does the big bang theory tell us about the
  early universe?
• All matter and energy in the early universe were
  compressed into a small volume at an extremely
  high temperature until the temperature cooled and
  all of the matter and energy were forced outward
  in all directions.

8
A Theory Emerges, continued

• Cosmic Background Radiation
• cosmic background radiation radiation uniformly
  detected from every direction in space
  considered a remnant of the big bang
• Astronomers believe that cosmic background
  radiation formed shortly after the big bang.
• The background radiation has cooled after the big
  bang, and is now about 270 C below zero.

9
A Theory Emerges, continued

• Ripples in Space
• Maps of cosmic background radiation over the
  whole sky look very smooth. But on satellite maps
  that show where temperatures differ from the
  average background temperature, ripples become
  apparent.
• These ripples are irregularities caused by small
  fluctuations in the distribution of matter in the
  early universe.
• The ripples are thought to indicate the first
  stages in the formation of the universes first
  galaxies.

10
A Theory Emerges, continued

• Timeline of the Big Bang

11
Big Bang Theory
Click below to watch the Visual Concept.
12
Universal Expansion
Click below to watch the Visual Concept.
13
A Universe of Surprises

• Dark Matter
• Analysis of the ripples in the cosmic background
  radiation suggests that the matter that humans,
  the planets, the stars and the matter between the
  stars makes up only 4 of the universe.
• About 23 of the universe is made up of a type of
  matter that does not give off light but that has
  gravity. This type of matter is called dark
  matter.

14
A Universe of Surprises, continued

• Dark Energy
• Most of the universe is made up of an unknown
  material called dark energy.
• Scientists think that dark energy acts as a force
  that opposes gravity. Many scientists think that
  some form of undetectable dark energy is pushing
  galaxies apart.
• Because of dark energy, the universe is not only
  expanding, but the rate of expansion also seems
  to be accelerating.

15
Maps In Action

• The Milky Way