Q18

[deedubbew]

A seems right to me. Can anyone explain why it is B?

[sexymidgetgem]

A seems right to me. Can anyone explain why it is B?

(A) cannot be an answer. Simply, "cohere" cannot be replaced by exert gravitational force because the meaning of the cohere is different from exert force. For better understanding I will give you an example, all thing in the universe exert gravitational force. Do you think all thing in the universe cohere each other?

(B) is good answer. Let's see the sentence.
In context, that sentence is the explanation of why neutrinos would be disqualified as dark matter.
Dark matter is something that covers the discrepancy of making huge structures cohere. And it is needed to explain why the universe is organized in the shape of galaxies and clusters of galaxies.
(B) fits very well in that context.

[ohthatpatrick]

Nice explanation! Let me add an official one since we don't have one for this question yet.

For this type of question, I normally go back to the line reference and attempt to generate some equivalent synonym on my own, before seeing the choices available in the answers.

For this chunk of text, I was thinking something like "make stuff stick together".

(A) Well, sure, "exerting gravitational force" leads to stuff sticking together. Keep it, I guess, although if we insert it into the text, the sentence reads,
"Without such gravitational force, matter can't induce other matter to exert gravitational force."

And remember that, in context, the "matter" we're referring to is neutrinos, if it turns out that they don't have mass.

(B) "form galactic structures" is definitely a specific form of "make stuff stick together". Is it too specific?

How do I know this reference to "cohering" was specifically about galaxies sticking together?

This is how the Main Point creeps into a Detail Question. The Main Point of this passage, like that of many Physical Science passages, begins with a question we couldn't answer / a riddle / a puzzling experimental result / a phenomenon.

In this passage, that puzzling result is that we don't see nearly as much mass in the universe as we think there should be. Why do we think that there SHOULD be more mass? Because that's how much mass there would need to be to gravitationally explain the existence of galactic structures.

In this passage, we're focusing on whether neutrinos might be supplying much of that "missing" mass.

So when we're saying "if neutrinos DIDN'T have mass, they wouldn't force objects to cohere", we're still talking about objects such as galaxies.

The easier way to see how "cohere" has this specific galactic meaning is to see that the same word was already used in line 17, "to make the huge structures cohere".

So the reference in line 30 is actually a callback to that line.

(C) Oscillating into a new type of matter comes outta nowhere and doesn't sound like "make stuff stick together"

(D) Becoming MORE massive is irrelevant; we want it to make different stuff stick together.

(E) Creating NEW particles is out of scope.

Hope this helps.

[sexymidgetgem]

Thank you for better explanation.

By the way, as I mentioned before, I believe cohere and answer(A) have significant gap in meaning. That is why I omitted answer(A). Is this approach incorrect ?

Cohere means to stick together or be united etc.
I believe cohere needs a physical bond or a physical movement instead of just exerting gravitational force.

For example, if there are a girl in Paris and boy in London. We know that they exert gravitational force. Yet, it doesn't mean they cohere or stick together.

For me, answer (B), (C), (D), (E) are good for replacing cohere because they make a physical bond or a physical movement to stick together.