After evidence was obtained in the 1920s that the universe is

Question

After evidence was obtained in the 1920s that the universe is expanding, it became reasonable to ask: Will the universe continue to expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? It can be calculated that the critical density of matter needed to brake the expansion and “close” the universe is equivalent to three hydrogen atoms per cubic meter. But the density of the observable universe—luminous matter in the form of galaxies—comes to only a fraction of this. If the expansion of the universe is to stop, there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70.

Our contribution to the search for this “missing matter” has been to study the rotational velocity of galaxies at various distances from their center of rotation. It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler’s law. Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.

Our findings suggest that  as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth . Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive. While it has not yet been determined whether this mass is sufficient to close the universe, some physicists consider it significant that estimates are converging on the critical value.   1 
 115. The passage is primarily concerned with

(A) defending a controversial approach
(B) criticizing an accepted view
(C) summarizing research findings
(D) contrasting competing theories
(E) describing an innovative technique

2 
 116. The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having

(A) higher rotational velocity and higher luminosity
(B) lower rotational velocity and higher luminosity
(C) lower rotational velocity and lower luminosity
(D) similar rotational velocity and higher luminosity
(E) similar rotational velocity and similar luminosity

3 
 117. The authors’ suggestion that “ as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth ” (lines 34–37) would be most weakened if which of the following were discovered to be true?

(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
(B) Luminous and nonluminous matter are composed of the same basic elements.
(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
(D) The density of the observable universe is greater than most previous estimates have suggested.
(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

4 
 118. It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?

(A) Luminosity would be a true indicator of mass.
(B) Different regions in spiral galaxies would rotate at the same velocity.
(C) The universe would continue to expand indefinitely.
(D) The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
(E) More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.

5 
 119. The authors propose all of the following as possibly contributing to the “missing matter” in spiral galaxies EXCEPT

(A) massive black holes
(B) small black holes
(C) small, dim stars
(D) massive stars
(E) large planets

blueseas · Accepted Answer

117. The authors’ suggestion that “as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth” (lines 34–37) would be most weakened if which of the following were discovered to be true?

(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
(B) Luminous and nonluminous matter are composed of the same basic elements.
(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
(D) The density of the observable universe is greater than most previous estimates have suggested.
(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

see the author is concluding :
Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth.
 (last para 1st line) 
 what is the basis of this conclusion:

It has been known for some time that outside the bright nucleus of  a typical spiral galaxy  luminosity falls off rapidly with distance from the center . If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler’s law. Instead  we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.

so author experiment is on TYPICAL galaxy  ==>some results came==>then he concluded.
see  the flaw i s he is considering only a limited source of galaxy and generalising for whole universe.

so the ultimate weakener that is option B: 
Spiral galaxies are  less common  than types of galaxies that contain little nonluminous matter.
SO this is saying that typical spiral galaxy are less number hence whatever conclusion author is trying to make can be wrong.

hope it helps

JarvisR · Answer

This can be done within 10 mins. I goofed up in 117 but then realized my mistake. 116 is tricky

115. The passage is primarily concerned with

(A) defending a controversial approach
(B) criticizing an accepted view
(C) summarizing research findings
(D) contrasting competing theories
(E) describing an innovative technique

116. The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having

(A) higher rotational velocity and higher luminosity
(B) lower rotational velocity and higher luminosity
(C) lower rotational velocity and lower luminosity
(D) similar rotational velocity and higher luminosity
(E) similar rotational velocity and similar luminosity

117. The authors’ suggestion that “as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth” (lines 34–37) would be most weakened if which of the following were discovered to be true?

(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
(B) Luminous and nonluminous matter are composed of the same basic elements.
(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
(D) The density of the observable universe is greater than most previous estimates have suggested.
(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

118. It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?

(A) Luminosity would be a true indicator of mass.
(B) Different regions in spiral galaxies would rotate at the same velocity.
(C) The universe would continue to expand indefinitely.
(D) The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
(E) More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.

119. The authors propose all of the following as possibly contributing to the “missing matter” in spiral galaxies EXCEPT

(A) massive black holes
(B) small black holes
(C) small, dim stars
(D) massive stars
(E) large planets

powerka · Answer

This OG RC passage has the first two questions on which I don't agree with the OA.

116.
Passage says: Velocity either remains constant with increasing distance from the center or increases slightly.
Question: compare "outermost regions" vs "region just outside the nucleus".
=> "region just outside the nucleus" could have either similar or lower velocity. 
=> Both B and D could be right; a case for D has strong foundations given that we are comparing the "region just outside the nucleus" with the "outermost region" -> greatest possible distance withing the galaxy.

117.
OA is A. I believe A is wrong. Explanation:
"Galaxies that contain little nonluminous matter" = dark matter (in the form of either dim stars, black holes or large planets). Thus, spiral galaxies being less common than "obscure" galaxies does not weaken the suggestion that "as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth".
D is the best answer. If the density of the observable universe (small fraction) is increased, that 90% would be lower; increase the fraction significantly, and you can have an observable reduction in that 90%.

icefrog · Answer

Completed within 10mins with 1 wrong.

Though I got 117 correct using POE :!: I would like to know the definite rationale to eliminate option D.

:

DmitryFarberMPrep · Answer

Notice that the author's assertion is not very precise: " as much as  90 percent of the mass . . . " So if we find that the observable universe is denser than we thought, it wouldn't really undermine this vague assertion. We would just adjust the maximum down by some unknown amount. Furthermore, the author's team is not basing their assertion on current estimates of the density of the observable universe, but on the observation of galaxies. This is why (A) presents a problem for this view. If it turned out that spiral galaxies like ours, which are rich in nonluminous matter, were uncommon, this would undermine the entire basis of the author's idea.

adkikani · Answer

Hi Experts /  GMATNinjaTwo

Q116:
As per passage:
 It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center
 which implies: as distance increases form center / nucleus, luminosity decreases.

Then why OA is D, I am clear about rotational velocity

GMATNinja · Answer

Yes, as distance from the center increases, luminosity decreases. This is consistent with choice (D): In comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having  higher luminosity . In other words, the luminosity is lower in the outermost regions than the luminosity just outside the nucleus.

We also know "that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly." This is also consistent with choice (D): In comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having  similar rotational velocity .

I hope that helps!

pkm9995 · Answer

Regarding question 117 this is my 10 cents.

(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.

Little nonluminous=No Nonluminous= Luminous

So it says Spiral galaxies are less common than galaxies that contain luminous matter.

As per the passage spiral galaxies contain dark matter and A says those galexies are less in number than those galexies which contain no dark matter. So as per this logic a can be considered as a weakener.

(B) Luminous and nonluminous matter are composed of the same basic elements.-  Density does not matter. We are talking about percentage of space occupied by luminous or nonluminous matter. So B is out.

(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter. - Does not matter

(D) The density of the observable universe is greater than most previous estimates have suggested.  -Again density. Density does not matter.We are talking about percentage of space occupied

(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured. -Does not matter

BrulesRules · Answer

Could someone please comment on 117 regarding answer D ?

if the density of the "observable universe" (defined in the passage as "luminous matter in the form of galaxies") com  to a small fraction of the   forms the basis for the assertion that "there must be enough INVISIBLE (nonluminous) matter in the universe to exceed the luminous matter by a density by a factor of roughly 70", then wouldn't this density estimate of the observable universe being understated (as answer D states) imply without room for refute that the assertion that nonluminous matter makes up 90% of the mass in the universe is weakened ???

Thanks for addressing this run on sentence. Seriously, this question (and the OG explanation) are quite off-target IMO - the official answer makes a much less airtight argument.

GMATNinja · Answer

The author does not argue that nonluminous matter must exceed luminous matter by a density factor of 70 BECAUSE that is what would be necessary to stop the expansion of the universe. Rather, the author merely comments that nonluminous matter  would have to  exceed luminous matter by a density factor of 70 IN ORDER TO stop the expansion of the universe.

Choice (D) would certainly affect the factor of 70 cited in the first paragraph; if there is more luminous matter than had been previously estimated, that would suggest that it would take less invisible matter to stop the expansion of the universe.

However, the author's suggestion mentioned in question #117 is based on the findings described in the second paragraph: "the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass."

The author believes that those findings "suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth." Choice (D) does not affect the author's reasoning at all. The author is using observations of  spiral galaxies  to draw conclusions about the universe. Choice (A) suggests that, even if the findings are true, they do not accurately reflect what's going on in most galaxies.

I hope that helps!

BillyZ · Answer

Passage: Expanding Universe

Question: Weaken

The Simple Story

The passage first proposes a question: will the universe keep expanding forever, or will it eventually stop? In order for the universe to stop expanding, there would have to be a large amount of invisible matter in the universe. The passage then describes a specific scientific investigation into the presence of invisible matter. The investigation has shown that this “dark matter” is, in fact, present in large quantities, but it is not clear whether there is enough to stop the expansion of the universe.

Sample Passage Map

Here is one way to map this passage. (Note: abbreviate as desired!)

univ. keeps expanding? ← yes, if lots of invis. matter

exper. shows: invis. matter in spiral galaxies

but: enough to stop expansion??

Step 1: Identify the Question

The phrase would be most weakened is unusual in a Reading Comprehension question stem. In the context of a Critical Reasoning problem, it would indicate a Weaken the Argument question. Use that same process to answer this question.

Step 2: Find the Support

In order to answer this question, you’ll need to understand why the authors believe that up to 90% of the mass of the universe is dark matter. Their argument is given in the second paragraph.

Step 3: Predict an Answer

The authors’ argument is based on the rotational velocity and luminosity of spiral galaxies.  If a part of a galaxy is rotating more quickly, it has more mass.  However, parts of these galaxies that don’t appear to have much mass are also rotating quickly. The authors conclude that there is invisible mass in these parts of the spiral galaxies—it can’t be seen, but it is still there, affecting rotation speeds.

In order to weaken this claim, consider the assumptions that the authors are making. They’ve investigated a specific set of galaxies and found evidence that, in those galaxies, the  rotational velocity is higher than expected . In concluding that up to 90% of the universe is dark matter, the authors are assuming several things. They’re assuming that there isn’t some other cause for the unexpectedly high rotational velocity. They’re also assuming that their observations were accurate. Finally, they’re assuming that these spiral galaxies are representative of the universe as a whole. The right answer could attack any of these assumptions.

Step 4: Eliminate and Find a Match

(A) CORRECT. This answer attacks the assumption that spiral galaxies are an accurate representation of the universe as a whole. If there are only a few spiral galaxies in the universe, it doesn’t matter that they contain a lot of dark matter. There would still be a relatively small amount of dark matter in the universe overall.

(B) The authors don’t make any claims about the composition of luminous and nonluminous matter, and there’s nothing in the passage that would link the composition of these types of matter to their prevalence in the universe.

(C) This would actually support the authors’ claim. If this were true, there would be even more nonluminous matter than the authors anticipated.

(D) If the density of the observable universe were greater, this would imply that there was more luminous matter in the universe. However, the authors’ research doesn’t draw conclusions about the overall amount of dark matter in the universe. Instead, they conclude, based on their observations of spiral galaxies, that dark matter represents a certain percentage of the universe. Even if there were much more luminous matter, there might simply be much more dark matter, as well, so that the percentages observed remained consistent—and the authors’ claim would still be valid.

(E) Unless these slow-rotating galaxies would disprove the authors’ claim by containing less dark matter than expected, this doesn’t affect the argument. This answer choice says nothing about the amount of dark matter in the hypothetical slow-rotating galaxies, so it is equally likely to strengthen the argument, weaken it, or have no effect.

bpdulog · Answer

Hi,

Where in the passage does it says that spiral galaxies are less common? I do not see that in the passage

DmitryFarberMPrep · Answer

bpdulog  The line you're quoting is exactly what supports D. The question is asking us to say how the region just outside the nucleus (i.e. near the center) compares to the outer regions. If luminosity falls off and we see more nonluminous mass as we go away from the center, that means that the center is more luminous, and that's what D states.

DmitryFarberMPrep · Answer

As for 117, take another look at what they're asking us to find. This isn't a detail or inference question, but a weakener. So when we select A, we're not saying it is true. We're saying that IF it were true, it would weaken the argument made in lines 34-37. It works for that purpose, because the author uses spiral galaxies as the basis for determining how much nonluminous matter there is likely to be in the universe. If spiral galaxies were not very common, and instead most galaxies were made almost entirely of luminous matter, that would make the author's assertion less likely.

GittinGud · Answer

Q4(118) - What's the relation between density of hydrogen atoms/m3, density of luminous matter and density of non luminous matter? How does the previous relationship affect universe expansion? This is very confusing.

honneeey · Answer

Hi,
If rotational velocity either remains constant or increases slightly, then why not (A) also.

KB04 · Answer

P1: Will the universe continue to expand? Critical Density = 3H to close the universe, but it’s very low; close universe – enough invisible matter to exceed the luminous matter in density.

P2: Search for missing matter – study rotational velocity of galaxies from the center of rotation; Proven wrong: Luminosity falls of rapidly with distance from center; Proven: Luminosity is balanced by an increase the nonluminous mass

P3: 90% of the mass of universe in not radiating any wavelength and it CAN be helpful to find out if the universe will continue to expand.

The passage is primarily concerned with

(A) defending a  controversial  approach
(B)  criticizing  an accepted view
(C)  summarizing research findings 
(D) contrasting  competing theories 
(E) describing an  innovative  technique

The authors’ study indicates that, in comparison with the outermost regions of a typical spiral galaxy, the region just outside the nucleus can be characterized as having

(A) higher rotational velocity and higher luminosity
(B) lower rotational velocity and higher luminosity
(C) lower rotational velocity and lower luminosity
(D) similar rotational velocity and higher luminosity
(E)  similar rotational velocity and similar luminosity

“This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.”

The authors’ suggestion that “as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth” (lines 34–37) would be most weakened if which of the following were discovered to be true?

(A) Spiral galaxies are less common than types of galaxies that contain little nonluminous matter.
(B) Luminous and nonluminous matter are composed of the same basic elements.
(C) The bright nucleus of a typical spiral galaxy also contains some nonluminous matter.
(D) The density of the observable universe is greater than most previous estimates have suggested.
(E) Some galaxies do not rotate or rotate too slowly for their rotational velocity to be measured.

Thank you  GMATNinja , your reply to this question was very helpful.

It can be inferred from information presented in the passage that if the density of the universe were equivalent to significantly less than three hydrogen atoms per cubic meter, which of the following would be true as a consequence?

(A) Luminosity would be a true indicator of mass.
(B) Different regions in spiral galaxies would rotate at the same velocity.
(C)  The universe would continue to expand indefinitely. 
(D) The density of the invisible matter in the universe would have to be more than 70 times the density of the luminous matter.
(E) More of the invisible matter in spiral galaxies would have to be located in their nuclei than in their outer regions.

“Will the universe continue to expand? Critical Density = 3H to close the universe, but it’s very low; close universe – enough invisible matter to exceed the luminous matter in density.”

The authors propose all of the following as possibly contributing to the “missing matter” in spiral galaxies EXCEPT

(A) massive black holes
(B) small black holes
(C) small, dim stars
(D)  massive stars 
(E) large planets

“Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive.”

GMATNinja · Answer

GittinGud , the concepts in this passage can be confusing! Breaking the relevant part of the passage down into smaller chunks can help establish that relationship:

This sentence tells us that there needs to be a density of at least 3 hydrogen atoms per cubic meter to stop the expansion of the universe.

Here is where we get information about the luminous and nonluminous matter. This sentence tells us that the amount of luminous matter does not come close to reaching that 3 hydrogen atoms per cubic meter threshold. So, if the expansion of the universe is to stop, there must be a large amount of nonluminous.

Don't get too bogged down in the exact numbers -- to answer the question, we only need the information explained above. Here's the question again:
 
We know from the first excerpt of the passage that to  stop expansion  of the universe we need  at least three hydrogen atoms per cubic meter.  So, if the density is equivalent to  "significantly less"  than that number, we know that the universe will  not stop expanding.  This corresponds nicely to answer choice (C), which is the correct answer.

I hope this answers your question!

teaserbae · Answer

AjiteshArun   DmitryFarber 
Can you please help in Q1 ?
I marked B as the author is crticizing the accepted view regarding the rotational velocity 
I rejected C because the author is not summarizing he just told us about the findings

After evidence was obtained in the 1920s that the universe is

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GMAT Reading Comprehension (RC) Questions

After evidence was obtained in the 1920s that the universe is

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