The Cosmological Principle

Paragraph 1：Cosmologists attempt to understand the origin and structure of the universe as a whole. They begin their search with an assumption about the nature of the universe — namely, that in looking out from our vantage point in the cosmos, we see essentially the same kind of universe that an observer stationed in any other part of it, no matter how remote, would see. As far as our telescopes can reach, we see galaxies and clusters of galaxies distributed in more or less the same way in every direction. This assumption that the universe is uniform on a large scale is called “the cosmological principle.” 

 

 

 

1. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. 

 

O Cosmologists make the assumption that the universe would appear basically the same from anywhere within it.

 

O Cosmologists simplify their assumptions because they are basically trying to understand the whole universe. 

 

O Cosmologists make an assumption about the universe basically in an effort to avoid stationing observers in remote places. 

 

O Cosmologists incorrectly assumed the universe to be far simpler that it really is when viewed on a larger scale. 

 

 

 

 

 

Paragraph 2：One thing that is certain is that the universe is expanding. In every direction we look, distant galaxies are moving away from each other. Until the 1960s, the expansion of the universe was the primary fact of cosmological significance that cosmological theories had to accommodate. There were two general classes of cosmological theories that fit with the expanding universe: the evolutionary (Big Bang) theory and the steady-state theory. 

 

2. According to paragraph 2, what is true of both the evolutionary and steady-state theories? 

 

O Both were based on the work of the same observer of the galaxies. 

 

O Both were used to overturn the theories of the early twentieth century. 

 

O Both took 30 years to become widely accepted by cosmologists. 

 

O Both accommodate the fact that the galaxies are moving apart.

 

 

 

 

 

Paragraph 3：The essential idea of the evolutionary cosmology is that there was a beginning—a moment of creation at which the universe came into existence in a hot, violent explosion—the Big Bang. In the beginning, the universe was very hot, very dense, and very tiny. As the explosion evolved, the temperature dropped, the distribution of matter and energy thinned, and the universe expanded. From the current observed rate of expansion, we conclude that the creation event occurred between ten and twenty billion years ago. 

 

 

3. According to paragraph 3, which of the following is NOT a feature of the Big Bang cosmology? 

 

O A sudden, hot explosion of the universe 

 

O A reduction in the density of matter over time 

 

O A significant rise in temperature over time

 

O An expansion of the universe 

 

 

 

 

 

Paragraph 4：The steady-state theory is based on an idea called the “perfect cosmological principle.” It is “perfect” in that it maintains that the universe is uniform not only in space but in time. Thus it is the hypothesis that the large-scale universe has always been the way it is now and will be this way forever in the future. This view is consistent with philosophical approaches that reject the notion of an absolute beginning of the universe as unacceptable. The steady-state universe would have no beginning and no end. 

 

4. Why does the author state that “The steady-state universe would have no beginning and no end.”? 

 

O To present evidence against the steady-state view of the universe 

 

O To clarify why the steady-state view is attractive to certain philosophical approaches

 

O To contrast cosmology with philosophy 

 

O To indicate that the steady-state view is the most accepted cosmology 

 

 

 

Paragraph 5：In an expanding universe, the galaxies move away from each other, spreading matter more thinly over space. On the other hand, the perfect cosmological principle requires that the density of matter in the universe remain constant over time. To make the steady-state theory compatible with the expanding universe, its proponents introduced the notion of continuous creation. As the universe expands and the galaxies move farther apart, new matter—in the form of hydrogen—is introduced into the universe. The rate at which the hypothesized new matter is created is far too small for this creation to be detected with available instruments, but continuous creation provides just enough matter to form new stars and galaxies that fill in the space left by the old ones. Thus in the steady-state universe there is evolution of stars and galaxies, but the general character and the overall density of the universe remains unchanged over time. In this special sense, the steady-state universe itself does not evolve. 

 

5. Which of the following is true of the concept of “continuous creation”? 

 

O It suggests that hydrogen for new stars is created as galaxies move farther apart.

 

O It asserts that matter in the universe becomes denser as hydrogen is created. 

 

O It explains why the galaxies are moving away from each other. 

 

O It predicts a change in density of matter in the universe over time. 

 

 

 

6. According to paragraph 5, which of the following is characteristic of the steady-state theory? 

 

O The rate of expansion it predicts is too slow to be measured by current instruments. 

 

O New stars and galaxies are formed, but the large-scale properties of the universe remain the same.

 

O The density of matter changes over time as the universe evolves. 

 

O The creation of new galaxies will eventually stop the universe from expanding. 

 

 

 

 

 

Paragraph 6：Both of these views—steady-state and Bing Bang—allow for cosmic expansion. However, the discovery in the 1960s of a comparatively small star-like objects called quasars tipped the scales in favor of the Big Bang cosmology. Astronomers determined that almost all quasars are very distant. Given how bright quasars appear even at such great distances, astronomers concluded that quasars typically have an output of light that is 1,000 times greater than that of a whole spiral galaxy composed of billions of stars. 

 

 

 

7. Paragraph 6 answers which of the following questions about quasars? 

 

O What is the ratio of the number of quasars to the number of spiral galaxies? 

 

O Why was the discovery of quasars of importance for cosmologists?

 

O Why were quasars not discovered before the 1960s? 

 

O How do quasars produce so much light? 

 

 

 

 

 

Paragraph 7：Quasars are such distant objects that the light now reaching us from quasars left them billions of years ago. This means that when we observe quasars today we are seeing that state of the universe billions of years ago. Thus the fact that almost all quasars are very far away implies that earlier in the history of the universe quasars were developing more frequently than they are now. This evolution is consistent with the Big Bang theory. But it violates the perfect cosmological principle, and so it is inconsistent with the steady-state view. 

 

 

 

8. Which of the following best describes the relationship between paragraphs 6 and 7?

 

O Paragraph 6 makes a claim about support for the Big Bang cosmology and paragraph 7 describes how the distribution of quasars provides that support.

 

O Paragraph 6 describes the similarities between the steady-state and Big Bang theories, while paragraph 7 explains the differences between them. 

 

O Paragraph 6 presents a question about quasars while paragraph 7 provides several possible answers to that question. 

 

O Paragraph 6 describes the chemical composition of quasars while paragraph 7 describes the locations of quasars. 

 

 

 

 

 

Paragraph 7：Quasars are such distant objects that the light now reaching us from quasars left them billions of years ago. This means that when we observe quasars today we are seeing that state of the universe billions of years ago. ■Thus the fact that almost all quasars are very far away implies that earlier in the history of the universe quasars were developing more frequently than they are now. ■This evolution is consistent with the Big Bang theory. ■But it violates the perfect cosmological principle, and so it is inconsistent with the steady-state view.■ 

 

 

 

9. Look at the four squares [■] that indicate where the following sentence could be added to the passage. 

 

In turn this means that over a period of billions of years the large-scale distribution of the kinds of galaxies the universe contains has fundamentally changed.

 

Where would the sentence best fit? Click on a square [■] to add the sentence to the passage. 

 

 

 

 

 

10. Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points. 

 

Evolutionary and steady-state theories have been proposed to explain the large-scale structure of the universe.

 

 

 

Answer Choices 

 

O The Big Bang theory maintains that the continuous creation of matter is the explanation for why the universe is expanding at a constant rate. 

 

O While the steady-state cosmology rejects the belief that the universe has an end, it accepts the possibility that the universe had a beginning. 

 

O The distribution of quasars suggests that the large-scale structure of the universe has changed over time and thus makes the evolutionary theory more plausible than the steady-state theory. 

 

O The evolutionary theory maintains that the universe had a beginning with a high density explosion and has been expanding to yield a less dense distribution of matter ever since.

 

O The steady-state theory maintains that the expanding universe has existed forever, with new matter being continuously created to keep the large-scale density of matter the same as we observe it today.

 

O The extreme brightness of quasars is proof of an explosion that marked the beginning of the universe as hypothesized by the evolutionary cosmology. 

 

 

 

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