the universe

the expanding universe

Hubble measured the distances to galaxies. He also studied the motions of galaxies. In doing these things, Hubble noticed a relationship. This is now called Hubbles Law: The farther away a galaxy is, the faster it is moving away from us. There was only one conclusion he could draw from this. The universe is expanding! Figure 26.15 shows a simple diagram of the expanding universe. Imagine a balloon covered with tiny dots. When you blow up the balloon, the rubber stretches. The dots slowly move away from each other as the space between them increases. In an expanding universe, the space between galaxies is expanding. We see this as the other galaxies moving away from us. We also see that galaxies farther away from us move away faster than nearby galaxies.

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dark matter

We see many objects out in space that emit light. This matter is contained in stars, and the stars are contained in galaxies. Scientists think that stars and galaxies make up only a small part of the matter in the universe. The rest of the matter is called dark matter. Dark matter doesnt emit light, so we cant see it. We know it is there because it affects the motion of objects around it. For example, astronomers measure how spiral galaxies rotate. The outside edges of a galaxy rotate at the same speed as parts closer to the center. This can only be explained if there is a lot more matter in the galaxy than we can see. What is dark matter? Actually, we dont really know. Dark matter could just be ordinary matter, like what makes up Earth. The universe could contain lots of objects that dont have enough mass to glow on their own. There might just be a lot of black holes. Another possibility is that the universe contains a lot of matter that is different from anything we know. If it doesnt interact much with ordinary matter, it would be very difficult or impossible to detect directly. Most scientists who study dark matter think it is a combination. Ordinary matter is part of it. That is mixed with some kind of matter that we havent discovered yet. Most scientists think that ordinary matter is less than half of the total matter in the universe.

dark energy

We know that the universe is expanding. Astronomers have wondered if it is expanding fast enough to escape the pull of gravity. Would the universe just expand forever? If it could not escape the pull of gravity, would it someday start to contract? This means it would eventually get squeezed together in a big crunch. This is the opposite of the Big Bang. Scientists may now have an answer. Recently, astronomers have discovered that the universe is expanding even faster than before. What is causing the expansion to accelerate? One hypothesis is that there is energy out in the universe that we cant see. Astronomers call this dark energy. We know even less about dark energy than we know about dark matter. Some scientists think that dark energy makes up more than half of the universe.

the big bang theory

About 13.7 billion years ago, the entire universe was packed together. Everything was squeezed into a tiny volume. Then there was an enormous explosion. After this big bang, the universe expanded rapidly (Figure 26.16). All of the matter and energy in the universe has been expanding ever since. Scientists have evidence this is how the universe formed. One piece of evidence is that we see galaxies moving away from us. If they are moving apart, they must once have been together. Also, there is energy left over from this explosion throughout the universe. The theory for the origin of the universe is called the Big Bang Theory.

after the big bang

In the first few moments after the Big Bang, the universe was extremely hot and dense. As the universe expanded, it became less dense. It began to cool. First protons, neutrons, and electrons formed. From these particles came hydrogen. Nuclear fusion created helium atoms. Some parts of the universe had matter that was densely packed. Enormous clumps of matter were held together by gravity. Eventually this material became the gas clouds, stars, galaxies, and other structures that we see in the universe today.

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instructional diagrams

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questions

What explains the phenomenon that Hubble discovered?

a. the universe is becoming warmer

b. the universe is becoming cooler

-->  c. the universe is expanding

d. the universe is collapsing

Scientists believe dark energy can explain what phenomenon?

a. the creation of the universe

-->  b. the increasing rate of expansion of the universe

c. the collapse of the universe

d. the shape of the universe

The farther away a galaxy is

-->  a. the faster it is moving away from us

b. the slower it is moving away from us

c. the faster it is coming toward us

d. the slower it is coming toward us

What does it mean if light is red shifted?

-->  a. The object is moving away from the observer

b. The object is moving towards the observer

c. The object is slowing down

d. The object is moving perpendicular to the observer

The outside edges and interior of a galaxy rotate at the same speed. This is evidence for the existence of

a. gravitational lensing

b. the Big Bang

c. dark energy

-->  d. dark matter

Edwin Hubble used powerful telescopes to discover other galaxies.

-->  a. true

b. false

As the distance between galaxies grows, the size of each galaxy shrinks.

a. true

-->  b. false

When the universe began, it was much larger than it is today.

a. true

-->  b. false

In the first few moments after the Big Bang, the universe was very hot and dense.

-->  a. true

b. false

The first matter to form in the universe consisted of protons, neutrons, and electrons.

-->  a. true

b. false

Redshift is the shift of absorption bands toward the red end of the spectrum.

-->  a. true

b. false

Hubbles Law states, the farther away a galaxy is, the faster it is moving away from us.

-->  a. true

b. false

Scientists think that stars and galaxies make up only a small part of the matter in the universe.

-->  a. true

b. false

Scientists have proven conclusively that dark matter and dark energy exist.

a. true

-->  b. false

Redshift was discovered by Edwin Hubble.

-->  a. true

b. false

The nature of dark matter is unknown.

-->  a. true

b. false

idea that explains how the universe formed

a. universe

-->  b. Big Bang theory

c. ordinary matter

d. dark matter

e. Hubbles law

The universe contains about a hundred million galaxies.

a. true

-->  b. false

matter that can be detected only by its effects on the motion of objects around it

a. universe

b. Big Bang theory

c. ordinary matter

-->  d. dark matter

e. Hubbles law

observation that the farther away a galaxy is, the faster it is moving away from us

a. universe

b. Big Bang theory

c. ordinary matter

d. dark matter

-->  e. Hubbles law

less than half of the total matter in the universe

a. universe

b. Big Bang theory

-->  c. ordinary matter

d. dark matter

e. Hubbles law

all the matter and energy that exists and all of space and time

-->  a. universe

b. Big Bang theory

c. ordinary matter

d. dark matter

e. Hubbles law

According to the Big Bang theory

a. dark matter is changing to ordinary matter throughout the universe.

b. dark energy is pulling the universe into black holes.

c. the universe will someday end because of a big bang.

-->  d. the universe began with an enormous explosion.

From our point of view in the Milky Way Galaxy, all other galaxies in the universe appear to be

a. crowding closer together.

-->  b. moving away from us.

c. getting dimmer.

d. growing larger.

After the big bang occurred, the universe

a. shrank in size.

b. became denser.

c. became hotter.

-->  d. began to cool.

Most scientists who study dark matter think that it is

-->  a. a mix of ordinary matter and matter we havent yet discovered.

b. matter that makes up black holes.

c. just a tiny fraction of all the matter that exists in the universe.

d. none of the above

Scientists recently discovered that the universe

a. has started to contract in size.

-->  b. is expanding even faster than before.

c. is no longer expanding or contracting.

d. will soon go through another big bang.

Scientists have introduced the concept of dark energy to explain the

-->  a. rate of growth of the universe.

b. contraction of the universe.

c. origin of dark matter.

d. all of the above

diagram questions

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