Question 18.1

Which force in nature is believed to have formed second?

• a. gravity
• b. electromagnetic force
• c. weak force
• d. strong force
• e. all formed at the same time

555

Question 18.2

Inflation most directly explains which of the following?

• a. Why the universe is homogeneous
• b. Why the universe is expanding
• c. Why the universe is going to last forever
• d. Why the universe has a background temperature
• e. Why the universe has particles

Question 18.3

What does it mean when astronomers say that we live in an expanding universe?

Question 18.4

Explain the difference between a Doppler redshift and a cosmological redshift.

Question 18.5

In what ways are the fate of the universe, the shape of the universe, and the average density of the universe related?

Question 18.6

Assuming that the universe will expand forever, what will eventually become of the microwave background radiation?

Question 18.7

What does it mean to say that the universe is dark-energy–dominated? When was the universe radiation-dominated? When was it matter-dominated? How did radiation domination show itself?

Question 18.8

Explain the difference between an electron and a positron.

Question 18.9

Where do astronomers believe most of the photons in the cosmic microwave background originated?

Question 18.10

Give examples of the actions or roles of each of the four basic physical forces in the universe.

Question 18.11

What is the observational evidence for the (a) Big Bang, (b) inflationary epoch, and (c) confinement of quarks?

Question 18.12

Explain why the detection of cosmic microwave background radiation was a major blow to the steady-state theory.

Question 18.13

Some so-called “creation scientists” claim that the universe came into existence 6000 years ago. What is Hubble’s constant for such a cosmos? Is this a reasonable number? Explain your answers.

Question 18.14

Discuss the implications of the fact that science cannot yet tell us what caused the Big Bang or what, if anything, existed before the Big Bang occurred.

Question 18.15

Explain why gravitational attraction has dominated the behavior of the universe until recently and why the dark energy determines the fate of the universe.

Question 18.16

The universe were destined to collapse and the collapse was underway? What would be different in space and on Earth under those conditions?

Question 18.17

Our solar system formed very early in the evolution of our Galaxy, when the universe was just 2 billion years old? What would be different in space and on Earth?

Question 18.18

Our solar system formed much later in the evolution of the universe than it actually did? How would observations of stars and galaxies be different than they are now?

Question 18.19

Our solar system formed with the first generation of stars? What would be different about the solar system? Would Earth exist as an inhabitable world? Why or why not?

Question 18.20

Structure of the Early Universe. Search the Web for information about the Planck spacecraft, which was mapping the universe until October, 2003. In what ways was Planck an improvement over the WMAP mission? What new insights do scientists hope to gain about the cosmos from Planck? What have they already learned from it?

Question 18.21

Which of the following best describes the overall motion in the universe:

• a. The universe is expanding faster and faster.
• b. The universe is expanding but more slowly all the time.
• c. The universe is expanding at a constant rate.
• d. The universe is collapsing at a constant rate.
• e. The universe is collapsing faster and faster.

Question 18.22

What is the weakest force in nature?

Question 18.23

What do astronomers believe to be the fate of the universe?

Question 18.24

Has the universe existed forever? If not, when did it come into existence?

Question 18.25

In an attempt to explore the far reaches of the Universe, the Hubble Space Telescope (HST) took long-exposure images of very dark regions of space that appear to contain no bright stars or galaxies. These images, known as the Hubble Deep Field and Hubble Ultra Deep Field images, reveal very rich fields of faint and very distant galaxies. The light now arriving at Earth from some of these galaxies has traveled over 13 billion years and was collected by the HST at a rate of a few photons per minute! This light was emitted very early in the life of the universe, only a few 100 million years after the Big Bang. You can examine and measure these two images. (a) In Starry Night™, open the Options pane, and ensure that the Hubble Images option is checked in the Deep Space layer. Open the Find pane, ensure that the search edit box is empty, and click on the icon in this box to display a list of image sources. Click on Hubble Images, and double-click on Hubble Deep Field to center the view on this dark region of space. Note its position with respect to the Big Dipper. (Note: If you cannot identify this region of the northern sky, click on View > Constellations > Asterisms and View > Constellations > Labels. Remove these indicators after you have identified the region.) Zoom in to a field of view about 3° wide and note that the region still appears to be devoid of objects. Zoom in again until the Hubble Deep Field (HDF) fills the view. One-quarter of the full HDF, with dimensions of 1.15′ × 1.15′, is displayed in Starry Night™. The bright object with spikes radiating from it is a star in our own Galaxy (the spikes are caused by diffraction by the supports for Hubble’s secondary mirror), but all of the other objects that appear on this long-exposure image are galaxies containing millions of stars. Examine this image carefully and attempt to identify some examples of each kind of galaxy—spiral, barred spiral, elliptical, and irregular—in this field. Choose five or six of the larger galaxies in this field, record their shapes and galaxy types, and use the angular separation tool to measure carefully and record their angular dimensions. (b) Click the Zoom panel in the toolbar, and select 90° from the dropdown menu. Return to the Find pane and the list of Hubble Images, and double-click on Hubble Ultra Deep Field (HUDF) to center the view of this “dark” region of the sky. Zoom in on this region and note that, even at a field of view as small as 2°, no objects can be seen in the position of this long-exposure image. Zoom in further until the full HUDF, with dimensions of 3.3′ × 3.3′, fills the field of view to see this rich field of faint and very distant galaxies. Examine this image carefully and attempt to identify some examples of each kind of galaxy—spiral, barred spiral, elliptical, and irregular—in this field. Again, select five or six of the larger galaxies in this field, record their shapes and galaxy types, and use the angular separation tool to measure their dimensions. (c) Consider the mix of different kinds of galaxies and assess whether the proportions of different kinds are the same in these two images. Compare the angular sizes of the largest galaxies in these two images.