Ch. 4 Sec. 5The Expanding

Universe

Discover activity-How Does the Universe Expand pg. 148

1. What happens to the distances between galaxies that are close together?

2. What happens to the distances between galaxies that are far apart?

3. If the universe is expanding, do galaxies that are close together move apart faster or slower than galaxies that are far apart? Explain.

Big Bang Theory• theory that universe formed in an instant, billions of yrs. ago, in an enormous explosion

Video clip-The Big Bang

Edwin Hubble• discovered :

1.galaxies are moving away from us & each other

2. relationship between distance to a galaxy & its speed

Hubble’s law•farther away galaxy is faster it is moving away from us

Video clip- Moving Galaxies

The galaxies in the universe are like the raisins in rising bread dough.

How does rising raisin bread dough resemble the expanding universe?

cosmic background radiation

• faint radiation glow that comes from all directions in space

• leftover thermal radiation from the big bang

How old is the universe?

13.7 billion years old

Video clip-Cosmic background radiation

Formation of the solar

system

1. 5 billion yrs. ago,

solar nebula (giant cloud of gas & dust) collapsed to form our

solar system

2. Gravity pulled solar

nebula together

3. Solar nebula shrank &

began spinning very fast

4. Solar nebula flattened- formed a rotating disk

5. Gravity pulled gas into center- nuclear fusion

began- sun born

6. Remaining gas & dust formed planetesimals-

formed planets

dark matter

•matter that does not give off electromagnetic radiation

•23% of universe’s mass

dark matter

•cannot be seen directly-presence can be inferred by effects of its gravity on visible objects

Video clip-Dark Matter

dark energy•force causing expansion of universe to accelerate

What was the big bang?

• Giant explosion after which all of the matter in the universe began moving apart

When did the big bang occur?

• About 13.7 billion years ago

Describe two pieces of evidence that support the

big bang theory?

1. Hubble’s law- the observation that the farther away a galaxy is, the faster it is moving away from Earth

2. cosmic background radiation-radiation left over from the big bang

How old is the solar system?

• About 5 billion years old

What force caused the solar system to form?

• Gravity pulled the solar nebula together and them pulled most of the gas into the center of the disk, where the gas eventually became hot and dense enough for nuclear fusion to begin and form the sun

Place the following events in the proper order:

• planets form

• planetesimals form

• solar nebula shrinks

• nuclear fusion begins in the sun

What is dark matter?

• Matter that does not give off electromagnetic radiation

How do scientists know that dark matter exists?

• Its presence can be inferred by observing the effect of its gravity on visible objects, such as stars, or on light

What evidence has led scientists to predict that the

universe will continue to expand forever?

• The expansion rate of the universe appears to be increasing.