The Big Bang model posits that the universe was created in a primordia

Question

The Big Bang model posits that the universe was created in a primordial fireball between 10 and 20 billion years ago. The model attempts to reconstruct the behavior of the early universe using only the rules of general relativity, elementary particle physics, and basic thermodynamics. Matching these claims with observations of the universe today shows its validity.

The Big Bang produced a universe made almost entirely of hydrogen and helium. For the first few seconds of the universe’s existence, its temperature was so high—over 10 billion degrees—and energetic electrons, neutrinos, and positrons so abundant that subatomic particles such as neutrons and protons were constantly transmuted into one another. As the universe cooled, these transmutations ceased. Most of the matter took the form of the most stable particle, the proton, leaving a universe where the ratio of protons to neutrons was about seven to one.

After a few minutes, the temperature of the universe fell to about 1 billion degrees, cool enough for these protons and neutrons to bond and form nuclei. Deuterons were formed as each neutron found a proton partner. Most deuterons then joined another deuteron to form a helium nucleus. As the universe continued to expand and cool, its density became too low to allow further fusion into heavier elements, and so almost all the neutrons were incorporated into helium. Only 0.01 percent of the deuterons formed remained unpaired, and an even smaller percentage had fused into elements heavier than helium, such as lithium.

Because only one neutron was formed for every seven protons, six-sevenths of all protons remained isolated. These remaining protons formed hydrogen nuclei containing one proton each. The Big Bang model predicts that about three-quarters of the total mass of the universe will be hydrogen and the remaining quarter helium. This simple prediction matches observations very well.   1  
 1. The author is primarily concerned with

A. explaining how the evolution of the universe is incompatible with the implications of the Big Bang model.
B. chronicling the events that followed the creation of matter by the Big Bang.
C. explaining how helium was formed in the early life of the universe.
D. illustrating specific propositions of a model and showing how they have been supported by observation.
E. showing how the ratios of protons to neutrons created in the Big Bang dictated the final ratio of hydrogen to helium in the universe.

2  
 2. In the fourth paragraph, the author introduces information about the Big Bang model’s prediction for the molecular composition of the universe in order to

A. obviate the claim that six-sevenths of all protons remained isolated.
B. show that the remaining quarter of the total mass of the universe must be helium.
C. provide evidence for the veracity of the Big Bang model.
D. describe the means by which remaining protons formed hydrogen nuclei.
E. predict the results of a Big Bang.

3  
 3. According to the passage, which of the following was true during the first few seconds of the universe’s existence?

I. The great majority of neutrons were incorporated into helium molecules.
II. The temperature was not high enough to allow for the formation of deuterons.
III. Vast numbers of subatomic particles rapidly metamorphosed into other types of particles.

A. None
B. I only
C. III only
D. II and III only
E. I, II, and III

4  
 4. The author uses the first paragraph to introduce

A. a scientific model that the passage will show to be supported by modern evidence.
B. a theory of the origin of the universe that the passage will describe and attempt to refute.
C. a description of the theoretical basis for a scientific model and the modern evidence undermining it.
D. an attempt to use recent evidence to revive a discarded scientific model.
E. a detailed description of an appealing but unsupported theoretical model.

5  
 5. The author would most likely agree with the position that

A. models of the creation of the universe that were made before the Big Bang model was created failed because they did not take into account the behavior of subatomic particles.
B. no credence can be given to a scientific model unless it is possible to produce supporting data through a series of controlled experiments.
C. the Big Bang was part of a cycle of expansion and contraction in the universe.
D. it is beneficial to use the statistical evidence at hand when judging the veracity of scientific models for which the process cannot be repeated in a laboratory.
E. the simplicity of the Big Bang theory accounts for its accuracy.

6  
 6. According to the passage, a helium nucleus

A. could only be created early in the universe’s history.
B. has a low density due to the cooling and expansion of the universe.
C. is more stable than a lithium nucleus.
D. has four times the mass of a hydrogen nucleus.
E. consists of exactly two neutrons and two protons.

Gmatsaiyan · Answer

Analysis 
The topic appears right away: the Big Bang model. The word “attempts” begs the question of whether the model succeeds. Aha! Indeed, the Big Bang model succeeded. And current observations demonstrate this.Lots of details about the Big Bang. Since we don’t want to read details too closely, we could try to get away just with saying “details about the Big Bang” in our map, but then paragraph 3 would be the same thing. So, we have to find some way of grouping these details. The passage gives us two sequences that let us do so easily: time (first few seconds) or temperature (so high and cooled).Once again, a ton of details about the Big Bang. If we’re using the time sequence, then this is the next few minutes. If we’re using the temperature sequence, then the universe continues to cool. Happily, we don’t need to understand a thing about particle physics to understand the basic structure of the passage!Still more details! These focus on the fact that the model’s predictions match observations, which (as we remember from paragraph 1) is why the model can be said to be valid.

Passage Map 
¶1: Introduce Big Bang model of the universe’s creation; it is valid
¶2: First seconds: temperature and energy high
¶3: After a few minutes: cooler, more stable
¶4: Observation confirms BB model
Topic: Big Bang Model
Scope: Validity of (B.B.M.)
Purpose: Demonstrate (the validity of the B.B.M.)

Gmatsaiyan · Answer

Official Answers and Explanations

Q1). (D)
The author is primarily concerned with
○○ explaining how the evolution of the universe is incompatible with the implications of the Big Bang model.
○○ chronicling the events that followed the creation of matter by the Big Bang.
○○ explaining how helium was formed in the early life of the universe.
○○ illustrating specific propositions of a model and showing how they have been supported by observation.
○○ showing how the ratios of protons to neutrons created in the Big Bang dictated the final ratio of hydrogen to helium in the universe.
Step 2: Analyze the Question Stem
The phrase “primarily concerned” in the question stem lets us know that this is a Global question.
Step 3: Research the Relevant Text
Using our Passage Map—particularly the topic, scope, and purpose—we should be able to predict the correct answer without having to reread any of the passage.
Step 4: Make a Prediction
From our scope and purpose notes, we can predict that the correct answer will say that the author is “demonstrating the Big Bang model’s validity.”
Step 5: Evaluate the Answer Choices
(D) is the only choice to mention that the passage addresses how observation supports the model’s propositions. (D) is the correct answer. (A) is a 180 trap; it claims that the Big Bang model isn’t valid. Change incompatible to compatible, and it would be correct. (B) focuses on the details from paragraphs 2 and 3 but does not address how those details fit within the passage as a whole. (C) claims that the passage is focused mainly on helium; the word helium certainly shows up a bit in paragraphs 3 and 4, but it isn’t the scope of the passage as a whole. (E) distorts details given in the passage. The author of the passage uses the ratios of hydrogen and helium to show us how well the Big Bang model matches observations. Choice (D) is correct.

Q2). (C)
In the fourth paragraph, the author introduces information about the Big Bang model’s prediction for the molecular composition of the universe in order to
○○ obviate the claim that six-sevenths of all protons remained isolated.
○○ show that the remaining quarter of the total mass of the universe must be helium.
○○ provide evidence for the veracity of the Big Bang model.
○○ describe the means by which remaining protons formed hydrogen nuclei.
○○ predict the results of a Big Bang.
Step 2: Analyze the Question Stem
This is a Logic question, because we are asked why the author used a specific piece of information. The question stem gives us a perfect reference—“the Big Bang model’s prediction for the molecular composition of the universe”—to guide our research.
Step 3: Research the Relevant Text
The reference from the question stem leads us to paragraph 4. Our Passage Map paraphrased paragraph 4 as showing that observation confirms the Big Bang model. Note that by doing our research
in the Passage Map first, we save ourselves from spending time rereading unnecessarily.
Step 4: Make a Prediction
From our research we can predict that the correct answer will say that the author included the details of the paragraph in order to “show us why the Big Bang model is valid.”
Step 5: Evaluate the Answer Choices
Our prediction matches very nicely with (C); this is the correct answer. The word obviate in (A) means “to avoid or eliminate.” The author believes it’s true that six-sevenths of all protons remained isolated, so (A) doesn’t make sense. (B) mixes things up; the author isn’t using the Big Bang model to prove that the universe is made up of certain kinds of molecules; instead, the author is using the molecular makeup of the universe to argue that the Big Bang model is valid. (D) incorrectly states that the author’s objective in this paragraph is to explain the how of hydrogen nucleus formation. The details of nucleus formation are discussed only to help the author make the case that the Big Bang theory is sound. (E) is wrong because the author, in the fourth paragraph, is not out to predict the
results of a Big Bang, but rather to validate the Big Bang model’s predictions. Choice (C) is correct.

Q3). (C)
According to the passage, which of the following was true during the first few seconds of the universe’s existence?
I. The great majority of neutrons were incorporated into helium molecules.
II. The temperature was not high enough to allow for the formation of deuterons.
III. Vast numbers of subatomic particles rapidly metamorphosed into other types of particles.
○○ None
○○ I only
○○ III only
○○ II and III only
○○ I, II, and III
Step 2: Analyze the Question Stem
The phrase “according to” in the stem signals a Detail question. So the right answer must be something that the author explicitly states. We also see that we’re looking for something that “was true during the first few seconds” of the universe.
Step 3: Research the Relevant Text
The Passage Map focuses our research on paragraph 2, specifically lines 7–10. We should notice that this sentence emphasizes temperatures that are “so high” and particles “so abundant” that constant change was the order of the day (or, at least, its first few seconds).
Step 4: Make a Prediction
The correct answer will agree with the ideas expressed in lines 7–10. Anything else must be incorrect because that’s the only place we learn about the “first few seconds.”
Step 5: Evaluate the Answer Choices
For Roman numeral questions, we should start with the statement that appears most frequently in the answer choices, which in this case is III. Lines 8–10 provide support for Statement III. Each
phrase and idea in Statement III matches directly with a phrase or idea from the passage: “vast numbers” matches with “so abundant,” “rapidly metamorphosed” matches with “constantly transmuted,”
and “subatomic particles” matches with, well, “subatomic particles.” Since Statement III is correct, eliminate (A) and (B). Next evaluate Statement II, as it appears in two of the remaining three choices. Researching line 7 shows that the temperature was “high” during the first few seconds of the universe’s existence. So, the phrase “not high enough” kills Statement II. That eliminates (D) and (E), leaving only (C). Choice (C) is the correct answer. Note that both Statements I and II refer to details from paragraph 3, which the time/sequence keywords show to describe not the first few seconds of the universe’s existence but rather the few minutes thereafter.

Q4). (A)
The author uses the first paragraph to introduce
○○ a scientific model that the passage will show to be supported by modern evidence.
○○ a theory of the origin of the universe that the passage will describe and attempt to refute.
○○ a description of the theoretical basis for a scientific model and the modern evidence undermining it.
○○ an attempt to use recent evidence to revive a discarded scientific model.
○○ a detailed description of an appealing but unsupported theoretical model.
Step 2: Analyze the Question Stem
This question stem asks for the purpose not of the whole passage, but of one of its parts. That makes this a Logic question. The stem makes clear reference to the first paragraph.
Step 3: Research the Relevant Text
As the question focuses on the whole of the first paragraph, our research can be focused on our
Passage Map. We wrote that paragraph 1 tells us what the Big Bang model is and that it’s valid, supported by observation of the universe.
Step 4: Make a Prediction
A reasonable prediction would be something like this: The author uses the first paragraph to introduce the Big Bang model and claim that it’s valid.
Step 5: Evaluate the Answer Choices
(A) matches our prediction perfectly. Every other answer choice gets the detail right (“theory” or “model”) but the purpose wrong: “refute,” “undermining,” “discarded,” and “unsupported” are all negative terms, while the author’s only purpose is to be positive. Choice (A) is correct.

Q5). (D)
The author would most likely agree with the position that
○○ models of the creation of the universe that were made before the Big Bang model was created failed because they did not take into account the behavior of subatomic particles.
○○ no credence can be given to a scientific model unless it is possible to produce supporting data through a series of controlled experiments.
○○ the Big Bang was part of a cycle of expansion and contraction in the universe.
○○ it is beneficial to use the statistical evidence at hand when judging the veracity of scientific models for which the process cannot be repeated in a laboratory.
○○ the simplicity of the Big Bang theory accounts for its accuracy.
Step 2: Analyze the Question Stem
The word “agree” makes this an Inference question, so the right answer must be true based on the passage but is likely not mentioned explicitly. This stem contains no reference to a particular detail
or paragraph.
Step 3: Research the Relevant Text
When the test asks you an Inference question without providing a particular reference to guide your research, prepare yourself to evaluate the answers by refreshing your memory on the topic, scope, and purpose.
Step 4: Make a Prediction
We cannot anticipate the exact wording of the correct answer, but since we are asked what the author would agree with, we know the right answer will be in line with “The Big Bang model corresponds
well with the observed universe; the model seems valid.”
Step 5: Evaluate the Answer Choices
(A) can be eliminated for two reasons. First, the passage only mentions the Big Bang model, not any others. So there’s no way we can state with confidence why any of those other models failed. Second, the author only ever uses positive opinion keywords, such as “validity.” So an answer about why something “failed” can’t be correct. (B) is a 180 wrong answer trap. The author gives credence to the Big Bang model, not by “a series of controlled experiments,” but by “matching . . . claims with observations.” (C) is incorrect because although the passage does mention “expansion” in line 17, there is no support for “contraction” or for “a cycle.” (Here is a case of something that is generally believed to be true in the world outside the GMAT but that is not actually supported by the passage.) The wording of (D) is convoluted and dense, but the passage supports everything here: “statistical evidence at hand” could well refer to “0.01 percent,” “six-sevenths,” or “three-quarters.” The author is indeed “judging the veracity of a scientific model.” The passage discusses the creation of the universe and its behavior, a “process which cannot be repeated in a laboratory.” But, more important than any of that is the fact that if the author didn’t believe (D), there’s no way he could say that the Big Bang model is valid. (D) is correct. (E) is a distortion of the last sentence. The author may agree that the Big Bang model is simple but not that this is what “accounts for its accuracy.” According to paragraphs 1 and 4, it is the model’s match with observation that demonstrates its validity. The correct answer is (D).

12. (E)
According to the passage, a helium nucleus
○○ could only be created early in the universe’s history.
○○ has a low density due to the cooling and expansion of the universe.
○○ is more stable than a lithium nucleus.
○○ has four times the mass of a hydrogen nucleus.
○○ consists of exactly two neutrons and two protons.
Step 2: Analyze the Question Stem
The phrase “according to” announces this as a Detail question, and the question gives us a clear reference for our research: “helium nucleus.”
Step 3: Research the Relevant Text
We know that the passage grows increasingly detail oriented in the third and fourth paragraphs. A quick scan reveals mention of the helium nucleus in line 16. The key to researching a detail is
its context. Here, the sentence on the helium nucleus (lines 15–16) tells us that it is formed of two deuterons. And the sentence right before that tells us that deuterons are made up of one neutron
and one proton.
Step 4: Make a Prediction
Our research shows that a good prediction for the correct answer choice is one that says the helium nucleus is made up of two deuterons or two protons and two neutrons.
Step 5: Evaluate the Answer Choices
The correct answer, (E), uses almost exactly the language of our prediction. (A) is too extreme. The passage does say that fusion stopped after the first few minutes. But it doesn’t say that fusion could
never happen under any other circumstance. Moreover, (A) distorts the passage, which claims that “fusion into heavier elements” stopped—not that fusion into helium itself stopped. (B) is a tricky distortion. The sentence following the reference to the helium nucleus says, “As the universe continued to expand and cool, its density became too low . . . .” But “its” refers to the universe, not the helium nucleus. Both (C) and (D) are out of scope, mentioned nowhere in the passage. (D), interestingly, happens to be a fact—you may recall from high school chemistry that a helium nucleus has four times the mass of a hydrogen nucleus. However, that fact is not mentioned in this passage, and it is not the correct response to a question asking for what’s true “according to the passage.” This answer is a good example of our caution against bringing in outside knowledge. Choice (E) is correct.

Sajjad1994 · Answer

Official Explanation

5. The author would most likely agree with the position that

Explanation

Analyze the Question Stem

The word  “agree”  makes this an Inference question, so the right answer must be true based on the passage but is likely not mentioned explicitly. This stem contains no reference to a particular detail or paragraph.

Research the Relevant Text

When the test asks you an Inference question without providing a particular reference to guide your research, prepare yourself to evaluate the answers by refreshing your memory on the topic, scope, and purpose.

Make a Prediction

We cannot anticipate the exact wording of the correct answer, but since we are asked what the author would agree with, we know the right answer will be in line with  “The Big Bang model corresponds well with the observed universe; the model seems valid.”

Evaluate the Answer Choices

(A)  can be eliminated for two reasons. First, the passage only mentions the Big Bang model, not any others. So there’s no way we can state with confidence why any of those other models failed. Second, the author only ever uses positive opinion keywords, such as  “validity.”  So an answer about why something  “failed”  can’t be correct.

(B)  is a 180 wrong answer trap. The author gives credence to the Big Bang model, not by  “a series of controlled experiments,”  but by  “matching . . . claims with observations.”

(C)  is incorrect because although the passage does mention  “expansion” , there is no support for  “contraction”  or for  “a cycle.”  (Here is a case of something that is generally believed to be true in the world outside the GMAT but that is not actually supported by the passage.)

The wording of  (D)  is convoluted and dense, but the passage supports everything here:  “statistical evidence at hand”  could well refer to  “0.01 percent,” “six-sevenths,” or “three-quarters.”  The author is indeed  “judging the veracity of a scientific model.”  The passage discusses the creation of the universe and its behavior, a  “process which cannot be repeated in a laboratory.”  But, more important than any of that is the fact that if the author didn’t believe  (D) , there’s no way he could say that the Big Bang model is valid.  (D) is correct .

(E)  is a distortion of the last sentence. The author may agree that the Big Bang model is simple but not that this is what  “accounts for its accuracy.”  According to paragraphs 1 and 4, it is the model’s match with observation that demonstrates its validity.

The correct answer is (D).

Hope it helps

Sajjad1994 · Answer

Official Explanation

Q6). According to the passage, a helium nucleus

Explanation

Step 1: Analyze the Question Stem

The phrase  “according to”  announces this as a Detail question, and the question gives us a clear reference for our research:  “helium nucleus.”

Step 2: Research the Relevant Text

We know that the passage grows increasingly detail oriented in the third and fourth paragraphs. A quick scan reveals mention of the helium nucleus. The key to researching a detail is its context. Here, the sentence on the helium nucleus tells us that it is formed of two deuterons. And the sentence right before that tells us that deuterons are made up of one neutron and one proton.

Step 3: Make a Prediction

Our research shows that a good prediction for the correct answer choice is one that says the helium nucleus is made up of two deuterons or two protons and two neutrons.

Step 4: Evaluate the Answer Choices

The correct answer,  (E) , uses almost exactly the language of our prediction.

(A)  is too extreme. The passage does say that fusion stopped after the first few minutes. But it doesn’t say that fusion could never happen under any other circumstance. Moreover,  (A)  distorts the passage, which claims that  “fusion into heavier elements”  stopped—not that fusion into helium itself stopped.

(B)  is a tricky distortion. The sentence following the reference to the helium nucleus says,  “As the universe continued to expand and cool, its density became too low . . . .”  But  “its”  refers to the universe, not the helium nucleus.

Both  (C)  and  (D)  are out of scope, mentioned nowhere in the passage.  (D) , interestingly, happens to be a fact—you may recall from high school chemistry that a helium nucleus has four times the mass of a hydrogen nucleus. However, that fact is not mentioned in this passage, and it is not the correct response to a question asking for what’s true  “according to the passage.”  This answer is a good example of our caution against bringing in outside knowledge.

Choice (E) is correct.

apoo151997 · Answer

1. Conclusion on the Deuteron StatementThe Takeaway: You cannot conclude that only two deuterons are joining based on the grammar of the sentence alone.Why: The phrase "most deuterons joined other deuterons" is grammatically ambiguous because it describes a plural crowd. To know it means pairs of two, you must bring in outside scientific context—specifically, the strict physical recipe of a helium nucleus, which only has room for a total of four particles (two deuterons).

2. Conclusion on the Transmutation StatementThe Takeaway: You cannot safely conclude that particles morphed into "other types" of particles.Why: The phrase "other types" introduces inaccurate, ambiguous information. The text specifies a closed loop where protons and neutrons changed "into one another" (swapping identities), not into brand-new, unmentioned categories of matter.

The Big Bang model posits that the universe was created in a primordia

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The Big Bang model posits that the universe was created in a primordia

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