Chapter 28 Stars and the Universe

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728 CHAPTER 28: STARS AND THE UNIVERSE science supplier works well. Swing the noisemaker in a circle around your head as people at a safe distance listen for changes in the pitch of the sound. Can the person swinging the device also hear the pitch of the sound change? For observers outside the circle, what part of the swing best represents redshift, and what part of the swing represents a “blueshift.” Two other factors supported Hubble’s hypothesis of an expanding universe. The redshift of light of distant galaxies could be observed in all directions. In addition, the dimmer galaxies, which are thought to be dim because they are farther from Earth, showed greater redshift. Hubble explained that the redshift is caused by motion of distant galaxies away from Earth. He also reasoned that this kind of motion is a characteristic of an explosion. You might think that the motion of distant galaxies away from Earth in all directions means that we are at the center of the expansion. However, from any position within the expanding matter of an explosion, matter is moving away in all directions. In the 1960s, Arno Penzias and Robert Wilson were working on long-distance radio communications for the Bell Telephone Company. They constructed a special outdoor receiver to detect weak radio signals. However, the device picked up annoying radio noise that they were not able to eliminate. As they investigated the source of these radio waves, they realized that the energy they were picking up was billions of years old. They were actually listening to the origin of the universe. These radio signals, known as cosmic background radiation, are weak electromagnetic radiation left over from the formation of the universe. The Big Bang The outward motions of distant galaxies and the cosmic background radiation are evidence that the universe began as an event now called the big bang. The name was first proposed as a joke to make fun of the theory, but the name stuck. This
theory proposes that at the time of its origin, the universe was a concentration of matter so dense that the laws of nature as we know them today did not apply. This matter expanded explosively, forming the universe. Even the most extreme conditions that exist within the largest stars could not compare with the beginning of the universe. Experiments and the theories of physics show that the greatest possible velocity for matter or energy is the speed of light: about 300 million meters per second. Like the temperature of absolute zero (0 K), this is one of the absolute limits known to science. Astronomers reason that the universe is expanding at this rate. By working backward, astronomers estimate that the universe began in the big bang 14 billion years ago. Expanding outward in all directions, the universe today could be as much as 28 billion light years across. This is so gigantic that it is nearly impossible for humans to comprehend how large this is. Earth, the solar system, and even the huge Milky Way Galaxy are incredibly small compared with the size of the universe. ACTIVITY 28-6 A MODEL OF THE BIG BANG WHAT IS THE FUTURE OF THE UNIVERSE? 729 Inflate a round balloon into a small ball. Draw several small dots on the balloon’s surface. Notice that as the balloon is inflated more, the dots always move apart. If observers were located anywhere on the surface of the balloon or even inside the balloon, as the balloon is inflated, they would see the dots moving away in all directions. No matter what location is chosen, it would appear that the observer is at the center of the expansion. Therefore, there is no way that astronomers can find the center of the universe. WHAT IS THE FUTURE OF THE UNIVERSE? From an astronomical point of view, Earth is in a reasonably unchanging state. Earth’s orbit around the sun is stable and scientists expect the sun to continue its energy production on
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Page 3 and 4: What Would We Answer? If scientists
Page 5 and 6: of energy. However, nuclear fusion
Page 7 and 8: Figure 28-3 When stars are plotted
Page 9 and 10: is apparent if you compare it with
Page 11 and 12: HOW DO ASTRONOMERS STUDY STARS? Sta
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Page 15 and 16: colors. You may need to rotate the
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Page 19: Figure 28-9 The sun and nearby gala
Page 23 and 24: TERMS TO KNOW Therefore, the ultima
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Chapter 28 Stars and the Universe

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