The document discusses the Big Bang theory of the formation and evolution of the universe. It states that according to this theory, approximately 13.7 billion years ago all matter in the known universe was compacted into a tiny, extremely dense particle that exploded, propelling matter and energy outward. Over millions of years, this matter cooled and came together to form galaxies that continue moving farther apart due to the ongoing expansion of the universe, as evidenced by the redshift of light from distant galaxies. The document also discusses evidence supporting the Big Bang theory, such as cosmic microwave background radiation, and competing theories like the steady-state theory.

1. Lesson 1
The Universe

2. The Big Bang Theory
The most widely accepted theory for the
formation of the universe is known as the
big bang theory
 According to this theory all matter was
once compacted in a tiny, dense particle
smaller than a piece of dust
 The particle was compacted by extreme
pressure and temperature until an
explosive event called the big bang
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3. The Big Bang Theory
Evidence suggests that the big bang
occurred approximately 13.7 billion years
ago
 In a fraction of a second, this explosion
propelled matter and energy outward in all
directions, forming the universe
 More than 300,000 years after the big
bang, some of this matter cooled to form
galaxies
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Galaxies are very large groups of stars and
associated matter that are found throughout
the universe

4. Evidence for the Big Bang
Scientists study the movement of galaxies
to help understand how the universe
formed
 These studies show that most galaxies
today are moving apart
 This observation indicates that the
universe continues to expand
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5. Evidence for the Big Bang
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To understand how galaxies are
moving look at the balloons to
the right
The balloon on the left is only
partly inflated
The dots on the balloons
represent galaxies
As more air is added to the
balloon, it expands, as shown
on the right
As the balloon expands its
“galaxies” move farther apart
The movement of the galaxies
on the balloon model is similar
to the movement of galaxies
observed by scientists
Galaxies

6. Evidence for the Big Bang
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After the explosion of the big bang, the matter and
energy of the universe would have started moving
outward in all directions
Evidence for the motion of galaxies comes from
the light they give off
The light from most galaxies is shifted toward the
red end of the spectrum
This red shift indicates that the galaxies are
moving away from Earth in all directions
The red shift provides evidence that the universe
is expanding
In the 1920’s Edwin Hubble demonstrated that the
farther away a galaxy is, the faster it is moving

7. Evidence for the Big Bang
Additional evidence supporting the big bang
theory was provided by the discovery of
cosmic background radiation in the mid
1960’s
 This weak radiation was found to be coming
from all directions of space
 The universe at the time of the big bang
would have been very hot, and would have
given off large amounts of infrared radiation
(thermal energy) and visible light
 As the universe has expanded, it has also
cooled
 The cosmic background radiation is thought
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8. Steady-State Theory
Not all scientists agree with the big bang
theory
 They don’t accept that the universe had a
definite beginning
 Another theory for the formation of the
universe is the steady-state theory
 This theory proposes that the universe has
always looked the same on a large scale
 And the theory states that the universe looks
the same in one location as it does in any
other location
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9. Steady-State Theory
Evidence that the universe is expanding
seems to contradict the steady-state
theory
 However, proponents of the steady-state
theory hypothesize that as the universe
expands, new matter is created
 In this way, the overall density of the
universe stays the same
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10. The Future of the Universe
Scientists use measurements from Earth
to various galaxies to estimate the age of
the universe and how it changes
 Such measurements indicate that the rate
of expansion of the universe is increasing
 It is not clear whether the universe will
continue to expand forever
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11. The Future of the Universe
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Some scientists hypothesize that at some point in
time, the expansion of the universe will slow down
Some believe that as more matter forms, gravitational
attractions between objects in space will prevent the
universe from continuing to expand
The pulsating universe theory suggests that once the
universe stops expanding, it will begin to contract and
collapse until it returns to its original state
In other words, the events resulting from the big bang
will take place in reverse until the universe contracts
back to a single point in a big crunch
Some scientists believe the universe will continue to
expand forever
Stars making up galaxies will age and die
As more stars die over billions of years, the universe
will eventually grow cold and dark