How Far is Far?
• Too far to measure with meters or
• How about a light-year?
• Nearest galaxy is _______ light-
• What we see happened
in the past
How Did it All Begin?
• How old is the universe?
• What was there before the
universe was created?
• What is the evidence?
• Measured movement of galaxies
• Found that all galaxies were
moving away from each other
• VERY unexpected
• Galaxies farther away moving
Big Bang Theory
The dominant scientific theory of the origin
of the universe.
Big Bang – The Theory
• The universe was once extremely dense
• A cosmic explosion occurred ~ 13-15
billion years ago
• Right after the explosion matter in the
universe was very hot and dense
• The universe has been expanding and
cooling since then
What Happened Next?
• At first, the universe was so hot and
dense that matter was very different
• Temperatures exceeded billions of
• As the universe expanded and cooled,
particles that make up atoms, like
quarks and electrons, formed
Cosmic Background Radiation
• In 1965 dim radiation was found
coming from apparently empty parts of
• Like long-lasting embers from a fire
• Cycles of expansion &
• Steady State
• Calculate backwards using
velocities of galaxies
• 13-15 billion years
What Happens Next?
There are possibilities….
• If the amount of matter in the
universe is enough……
• If not ……………