Dark Matter and Dark Energy - TOEFL iBT® Reading Practice Test

Dark matter and dark energy are mysterious components of the universe that have puzzled scientists for decades. Although invisible and undetectable by conventional instruments, dark matter is believed to make up about 27% of the universe, exerting gravitational forces that help hold galaxies together.

Even more mysterious, dark energy constitutes roughly 68% of the universe and is thought to drive the accelerated expansion of the cosmos. Together, these forces make up the vast majority of the universe's mass and energy, yet their nature remains largely unknown. This passage will explore what scientists know about dark matter and dark energy, how they were discovered, and why they are crucial to understanding the universe.

Reading Instructions:

• You have 15 minutes to read the following passage and answer all 9 questions related to it.
• Most questions are worth 1 point, but the last question is worth more. The directions indicate how many points you will receive for that specific question.
• The specific section/paragraphs have been provided again with the question for ease of understanding and quick solution.
• Some questions include a word or phrase that is highlighted in the question as well as in the paragraph for quick reference.

Directions: Once you have read the passage, answer the following questions.

Paragraph 1

The universe, as understood through modern astrophysics, is made up of a large array of things, with dark matter and dark energy being the most mysterious. Ordinary matter, which includes stars, planets, and living things, makes up only about 5% of the universe's total mass. In contrast, dark matter and dark energy together account for roughly 95%, with dark matter making up about 27% and dark energy about 68%. Dark matter does not emit, absorb, or reflect light, so we know it exists because of its gravitational effects on visible matter. On the other hand, dark energy is a mysterious force thought to be responsible for the fast expansion of the universe. Studying these two events has important effects on our understanding of the cosmos.

Factual Information Question

1. According to paragraph 1, what percentage of the universe's total mass is made up of ordinary matter?
   1. 5%
   2. 27%
   3. 68%
   4. 95%

Negative Factual Information Question

1. In paragraph 1, which of the following statements is NOT true?
   1. Dark matter accounts for about 27% of the universe's total mass.
   2. Dark energy is responsible for the slow expansion of the universe.
   3. Ordinary matter includes stars and planets.
   4. Dark matter does not interact with light.

Paragraph 2

Dark matter was first suggested in the early 20th century when astronomers noticed differences between the visible mass of galaxies and their spinning speeds. For example, the rotation curves of spiral galaxies showed that they were spinning much faster than expected based on their visible mass. This led to the idea that an unseen mass, which does not interact with electric forces, must be present. Later observations, like the gravitational lensing of light from distant galaxies, provided more evidence for dark matter's existence. The gravitational effects seen in galaxy clusters, especially in the Bullet Cluster, have strengthened the case for dark matter, as the visible matter does not explain the gravitational forces involved.

Inference Question

1. What can be inferred from paragraph 2 about the nature of dark matter?
   
   1. It interacts strongly with electric forces.
   2. It is visible through telescopes.
   3. It is likely to be a form of matter that does not emit light.
   4. It has been completely understood by scientists.

Paragraph 3

Despite the strong evidence for dark matter, its exact nature remains hard to find. Various candidates have been suggested, including Weakly Interacting Massive Particles (WIMPs) and axions. WIMPs are theoretical particles that would interact through the weak nuclear force and gravity, making them hard to detect. Axions are theoretical particles that could solve certain problems in particle physics, which studies the strong interactions between quarks and gluons. Many experiments are currently trying to detect these particles, but none have produced definite results so far. The ongoing search for dark matter is not just an academic exercise; it could change our understanding of basic physics.

Rhetorical Purpose Question

1. Why does the author mention WIMPs and axions in paragraph 3?
   
   1. To illustrate the complexity of dark matter.
   2. To provide examples of successful experiments.
   3. To suggest that dark matter is easily detectable.
   4. To argue against the existence of dark matter.

Paragraph 4

In contrast to dark matter, dark energy was introduced to explain the surprising finding that the universe's expansion is fast. In 1998, two independent teams of astronomers studying distant supernovae found that these celestial objects were dimmer than expected, suggesting they were farther away than previously thought. This led to the idea that a pushing away force, called dark energy, must be acting against the pull of gravity. Dark energy is thought to make up about 68% of the universe's total energy amount. The universe-related constant, first proposed by Albert Einstein in 1917, is one of the simplest explanations for dark energy, suggesting it is an unchanging energy amount filling space evenly.

Vocabulary Question

1. The word "dimmer" in paragraph 4 is closest in meaning to
   1. darker
   2. less bright
   3. smaller
   4. more distant

Paragraph 5

The effects of dark energy are deep, as they challenge our understanding of gravity and the future of the universe. If dark energy continues to control, the universe may face a scenario known as the "Big Freeze," where galaxies drift apart and stars eventually burn out, leading to a cold, dark cosmos. Or, if dark energy changes over time, it could lead to different outcomes, like the "Big Crunch," where the universe collapses back into a single point. Current observations suggest that dark energy is unchanging, but the possibility of it changing remains an area of active research. Understanding dark energy is important for predicting the long-term evolution of the universe and addressing key questions about its ultimate fate.

Sentence Simplification Question

1. Which of the following sentences best expresses the essential information in the following text from paragraph 5? "If dark energy continues to control, the universe may face a scenario known as the 'Big Freeze,' where galaxies drift apart and stars eventually burn out."
   
   1. The universe may become cold and dark if dark energy persists.
   2. Galaxies will always remain close together if dark energy changes.
   3. The universe will collapse into a single point if dark energy is constant.
   4. Stars will burn out quickly if dark energy is eliminated.

Paragraph 6

Studying dark matter and dark energy not only improves our understanding of the universe but also raises basic questions about the nature of reality itself. As researchers explore these phenomena, they face the limits of current theories and the need for new physics. For instance, while dark matter is inferred from gravitational effects, its hard-to-find nature raises questions about how complete our understanding of matter really is. The relationship between dark matter, dark energy, and the observable universe may eventually lead to a more unified understanding of the cosmos. As technology improves and new observational techniques are developed, the mysteries surrounding dark matter and dark energy may gradually become clearer, offering insights that could redefine our place in the universe. The quest to understand these elusive parts of the cosmos is not just a scientific effort; it is a deep exploration of existence itself, leaving many questions unanswered and inviting further investigation.

Purpose of the Passage Question

1. What is the main purpose of paragraph 6?
   
   1. To summarise the findings about dark matter and dark energy.
   2. To highlight the importance of studying dark matter and dark energy.
   3. To discuss the limitations of current scientific theories.
   4. To explain the relationship between dark matter and dark energy.

Insert Missing Sentence Question

1. In paragraph 6, there is a missing sentence. The paragraph is repeated below and shows four letters (A, B, C, and D) that indicate where the following sentence could be added.These discoveries could lead to revolutionary changes in our understanding of physics. Where would the sentence best fit?
   1. Studying dark matter and dark energy not only improves our understanding of the universe but also raises basic questions about the nature of reality itself.
   2. As researchers explore these phenomena, they face the limits of current theories and the need for new physics.
   3. For instance, while dark matter is inferred from gravitational effects, its hard-to-find nature raises questions about how complete our understanding of matter really is.

   4. The relationship between dark matter, dark energy, and the observable universe may eventually lead to a more unified understanding of the cosmos. 

Prose Summary Question

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 sentences 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.

Dark matter and dark energy are two of the most mysterious components of the universe, making up about 95% of its total mass. 

1. Dark matter and dark energy are two of the most mysterious components of the universe, making up about 95% of its total mass. 
   1. Dark matter is inferred from its gravitational effects, while dark energy is thought to be responsible for the universe's accelerated expansion.
   2. The search for dark matter involves theoretical particles like WIMPs and axions, which have yet to be detected.
   3. Understanding dark energy is crucial for predicting the future of the universe and its ultimate fate.
   4. The study of dark matter and dark energy raises fundamental questions about the nature of reality and the limits of current physics.
   5. The universe is primarily composed of ordinary matter, which includes stars and planets.

Prose Summary Question

1. Which of the following best summarises the overall message of the passage?  
   1. Dark matter and dark energy are essential for understanding the universe, yet they remain largely unexplained.,
   2. The universe is made up of ordinary matter, which is the most important component.
   3. Dark matter and dark energy are easily detectable and understood by scientists.
   4. The study of dark matter and dark energy has no significant implications for our understanding of the cosmos.

Answer Key with Explanation for TOEFL Reading Passage - Dark Matter and Dark Energy

1.  Answer: A
Explanation: The passage clearly states that ordinary matter, which includes stars, planets, and living things, constitutes only about 5% of the universe's total mass. This information is explicitly mentioned in the first paragraph, making it a straightforward factual detail.

2.  Answer: B
Explanation: The passage indicates that dark energy is responsible for the fast expansion of the universe, not a slow one. This makes option B the only statement that is not true according to the information provided in paragraph 1.

3.  Answer: C
Explanation: The passage mentions that dark matter does not emit, absorb, or reflect light, which implies that it is a form of matter that is not visible. Therefore, option C is a reasonable inference based on the information provided in paragraph 2.

4.  Answer: C
Explanation:  The mention of WIMPs and axions serves to highlight the complexity and the ongoing challenges in understanding dark matter. By discussing these theoretical particles, the author emphasizes that dark matter is not yet fully understood, which aligns with option A.

5.  Answer: B
Explanation:  In the context of the passage, "dimmer" refers to the brightness of the distant supernovae being less than expected. Therefore, the closest meaning to "dimmer" is "less bright," making option B the correct choice.

6.  Answer: A
Explanation:  This option effectively captures the essence of the original sentence, summarising the potential outcome of the "Big Freeze" scenario. It conveys the idea that if dark energy continues to dominate, the universe will become cold and dark, aligning closely with the original meaning.

7.  Answer: B
Explanation:  The main purpose of paragraph 6 is to underscore the significance of studying dark matter and dark energy, as it raises fundamental questions about reality and the limits of current scientific theories. This aligns with option B.

8.  Answer: B
Explanation:  The sentence "These discoveries could lead to revolutionary changes in our understanding of physics" fits best after option B, as it follows the discussion about the limits of current theories and the need for new physics, reinforcing the idea that new discoveries could significantly impact our understanding.

1.  Answer: A, B and C
Explanation:  A- accurately reflects the distinction between dark matter and dark energy and their roles in the universe. 
B- highlights the ongoing search for dark matter and the theoretical particles involved, which is a key point in the passage. 
C emphasizes the importance of understanding dark energy for predicting the universe's future, aligning with the passage's focus. D and E do not capture the main ideas presented in the passage.

10.  Answer: A
Explanation: This option encapsulates the overall message of the passage, which discusses the significance of dark matter and dark energy in the cosmos while also highlighting the ongoing mysteries surrounding them. It accurately reflects the central themes presented throughout the text. 

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