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Section 4: The Big Bang Theory


... astronomers have been able to determine that the universe is ... continued Reading Check What does the big bang theory tell us about the early universe? – PowerPoint PPT presentation

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Title: Section 4: The Big Bang Theory

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

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.

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.

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.

Hubbles Observations, continued
  • The Expanding Universe
  • Using Hubbles observations, astronomers have
    been able to determine that the universe is
  • 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.

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
  • By the mid-20th century, almost all astronomers
    and cosmologists accepted the big bang theory.

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.

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.

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
  • 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

A Theory Emerges, continued
  • Timeline of the Big Bang

Big Bang Theory
Click below to watch the Visual Concept.
Universal Expansion
Click below to watch the Visual Concept.
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

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.

Maps In Action
  • The Milky Way
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