CHAPTER 18

Arrange the steps in the history of the Universe, starting from the earliest (top). Instructions

1. inflation 2. protons and neutrons form 3. electrons and positrons annihilate. 4. helium forms 5. the microwave background is emitted. 6. stars form.

Match the average temperatures of the Universe with what was happening in it at the time it cooled to that value. Instructions

10^25k - inflation ends. 10^9k- helium is created 3000k- electrons recombine w hydrogen and emit light that eventually forms the CMB. 100k- stars and galaxies begin to form. 2.725k- humans live on earth.

Based on the current estimate of the Hubble constant being about 70 km/s per Mpc, it's been about ______ years since the Big Bang. Multiple choice question.

14 billion

The graph shows Hubble's law. If you measure a recession velocity of 15,000 kmsec , you can conclude that the distance to the galaxy is ___.

200 Mpc.

Hubble's law is V = H × d. Therefore, a galaxy moving away from us at 30,000 kms/ec must be three times as far away from us as one moving at ___ kms/ec . (Enter a whole number.)

10000.

Astronomers interpret galaxy recession velocities as evidence that the Universe is expanding. The "expansion of the Universe" means that ___ is expanding.

space.

In the balloon analogy for the expansion of the Universe (image), it looks like the center of the expansion is at A. However, you can tell there is no center to the expansion on the balloon's surface because ____.

buttons A and C moved as far from B as B and C from A.

Cosmology is the study of the ______.

structure and evolution of the universe.

There is no actual center or preferred direction to the universe. Therefore, everything looks the same from every location. Astronomers describe this idea as the_____ principle.

cosmological

is the study of the structure and evolution of the Universe

cosmology

_____energy is a property of space that seems to oppose gravity and causes the Universe to expand.

dark

Over time, as a Universe with a cosmological constant expands, the energy density of dark energy will stay constant, but the value of ΩM will ___.

decrease

To determine the balance of the expansion energy of the Universe to its gravitational energy (which causes the universe to collapse), ideally astronomers would measure the mass of the Universe. Since this is impossible, instead they measure its ____.

density

Whether or not the universe continues to expand or collapses under gravity depends on how much mass is contained, on average, within a given (large) volume. Therefore, astronomers try to compute the average___of the universe and compare to a critical value required for collapse.

density

True or false: On their way to us, the photons detected as the cosmic microwave background today have been absorbed and emitted many times since the last scattering epoch.

false

Shortly after 10-35 seconds after the beginning of time, the Universe expanded exponentially for a period of time, undergoing many doublings of size in a tiny fraction of second. This was ____.

inflation

The initial expansion of the Universe was caused by a process called ___, in which the size of the Universe doubled in size repeatedly over a number of equal time intervals.

inflation

Match the objects to the type of curvature they approximate. Instructions

potato chip- negative cutting board- no curvature soccer ball- positive

The Big Bang model is the only theory that successfully explains the presence of ____.

the cosmic background

Evidence demonstrates that Earth is not at the center of the Universe, nor is the Sun, nor even the Milky Way. In fact, there may not even be a unique center or any preferred location. This is a statement of ____.

the cosmological principle

George Gamow and other astronomers thought that elements should have been produced by the early Universe because ____.

the high temperature and density of the Universe would have been like that of the interiors of stars.

The cosmic horizon is ____.

the largest distance from which a signal can reach us if it has traveled for the whole age of the Universe.

The best explanation why some galaxies appear to be receding at more than the speed of light is that ______.

the space itself between the Milky Way and these galaxies is expanding, stretching the light rays passing through.

Since inflation, the cosmic horizon has expanded faster than the Universe (we see more of it with time). True or false: In the distant future, because of dark energy, galaxies we can see now will disappear over the horizon.

true

The cosmic microwave background (CMB) can be described as ____. (Select all that apply.)

very uniform in all directions blackbody radiation with a temperature of 2.725 K

Match the objects and their approximate ages.

- 14 billion years : The Universe. - 4.6 billion years : The Sun. - 13 billion years : The Milky Way, The oldest stars.

The conditions below are observed either in a space with negative curvature (saddle shape) or positive curvature (surface of a globe). Select only the choices that are associated with positive curvature.

- Angles of a triangle sum to more than 180° .- Parallel lines converge.

Select all that correctly describe dark energy.

- Dark energy accelerates the expansion of the Universe. - The influence of dark energy is expected to increase with time.

What can we expect the future Universe to look like? (Select all that apply.)

- In the very distant future, black holes will evaporate. - In the distant future, dead stars and other matter will collide to form black holes, which will also merge. - The Universe will get dimmer as the stars die out. - Eventually, objects we can see now will be receding so fast that their light will no longer be able to reach us. - Clusters of galaxies will become single massive galaxies.

Select all the true statements about the formation of elements in the early Universe. (Select all that apply.)

- It happened throughout the Universe. - It continued until about 24% of the Universe was helium. - It continued until the Universe cooled to temperatures below that of a stellar core.

Select all the premises that can be used to argue that the night sky should be bright (Olbers' paradox). Since the night sky is not bright, these are assumptions that must be investigated!

- There is an infinite number of stars. - The Universe has existed forever.

As we look at galaxies that are closer to the cosmic horizon, ____. (Select all that apply.)

- they are younger than nearer galaxies - they are farther away from us than nearer galaxies. - they are farther from us now than when the light we see was emitted.

Which of the following theories states that the Universe was born in a hot, dense state and expanded rapidly?

Big Bang Theory

The universe began with the ____ ____, and explosion from a tiny, hot, dense state.

Blank1-big Blank2-bang

Select the best description of the expansion of the Universe.

Everything is moving away from everything else.

How do scientists believe the Universe began?

It expanded from a tiny, dense size in a violent burst.

Why is the cosmic microwave background (CMB) such a perfect blackbody?

The Universe was a very uniform plasma at recombination.

Which statement describes Olbers' paradox?

The night sky should be bright, but it is not.

Select all the levels of the cosmological constants that could cause the universe to collapse.

Weaker than gravity Zero

Which is the best description of the cosmological constant? It is ____.

an energy that fills space at a constant level.