Q13 - Astronomers have found new evidence

[tzyc]

Is (A) correct because it does not matter how many galaxies actually exist since they are thought made up only small % of the universe's total mass?
So the actually % does not matter, since the stimulus only says "it is thought" or "their estimate"...
At first I eliminated it because I thought if there are actually way a lot (more than the number they found) number of galaxies-so it actually not a tiny percentage-then it would not explain the phenomenon...
And why is (D) wrong? the part of "how galaxies are formed"?

Thank you

[ohthatpatrick]

I think you're getting hung up on "thought to" and "estimated", when they are not really important facets of the answer/question.

Basically, here's our paradox:
1. We now think there are 50, not 10, billion galaxies
yet
2. The estimated mass of the universe is virtually unchanged.

(A) is telling us that the mass of galaxies has almost no effect on the mass of the universe, since galaxies represent a tiny percentage of the overall mass.

Suppose you had a van full of bowling balls and paperclips. Let's say we estimated the mass of the van and all its contents to be 8000 pounds.

Now suppose I told you, "Wait a sec ... there's not 1000 paperclips in there; there's 5000 paperclips."

Clearly, that wouldn't change your estimate of the total mass of the van much, because the paperclips were only adding negligible mass to begin with.

That's what (A) is getting at, only with galaxies = paperclips.

The phrases "thought to", "now believe", and "estimates" are all pretty interchangeable here, because the topic is about what scientists THINK is true.

We're trying to reconcile their beliefs, not actual facts.

They believed the mass of the universe was X.
They believed there were 10 billion galaxies.

Now that they believe that there are 50 billion galaxies, they still believe that the mass of the universe is X, because they believe that galaxies have almost no effect on the universe's total mass.

=== other answers ===

(B) Great, scientists can only make a rough estimate. Well, the question still remains, "Why isn't their rough estimate changing substantially now that they think there are 5 times as many galaxies?"

(C) This might help explain why we now think there are more galaxies, but it doesn't address the 2nd point, why our estimate of the universe's mass hasn't increased substantially.

(D) Galaxy formation had nothing to do with the paradox. The paradox is the tension between the first sentence and the last sentence. The middle sentence has nothing to do with the last sentence. Plus, we're trying to answer this question: "Given our new estimate of the # of galaxies, why isn't the estimate of the universe's total mass significantly affected?"

To answer that question, you would want to hear, "_____ rarely affects the estimate of the universe's total mass"
vs.
"____ is rarely affected by the estimate of the universe's total mass."

(E) This might be tempting to some. You could try to read into it, "Since some astronomers have their own opinion about the proper procedure for estimating total mass, maybe those astronomers believe that number of galaxies in the universe is not a relevant variable for calculating such an estimate."

This is telling ourselves too much of a story. All (E) says is that there is not total agreement about how to calculate total mass. We'd be adding too much to make up this story about some astronomers leaving "number of galaxies" out of the equation.

Hope this helps.

[topcow500]

I answered (E). I don't see why (A) should be correct outside of POE, but POE actually brought me to (E).

My problem with (A) is simple. What exactly is the definition of "tiny" as it relates to a percentage? Less than 1%? Less than 10%...20%? Additionally, would many scientists ignore this tiny change in mass?

There is no mathematical definition for the word "tiny." If they had said, in place of "tiny," "a fraction of a percentage" or something along those lines, then it would be slightly more obvious that (A) is correct. Perhaps they expect us to qualify "virtually unchanged" as a "tiny change," which seems to be quite a semantic leap with the lack of a definition.

On the other hand, by suggesting that there is no consensus among astronomers on the proper procedures for estimating the universe's total mass (E), then we can guess that MAYBE the number of galaxies doesn't factor heavily in this calculation to MANY (some) astronomers.

[inesa909]

I had a hard time choosing between answer choices (A) and (C) for this question and I was wondering if someone could offer a more detailed reason why (C) is wrong.

I understand that (C) didn't address the issue of the Universe's total mass, but it seems to me that more sophisticated instruments could still explain the discrepancy... perhaps this has everything to do with how the question is worded?

[sumukh09]

I had a hard time choosing between answer choices (A) and (C) for this question and I was wondering if someone could offer a more detailed reason why (C) is wrong.

I understand that (C) didn't address the issue of the Universe's total mass, but it seems to me that more sophisticated instruments could still explain the discrepancy... perhaps this has everything to do with how the question is worded?

C) is wrong because we need to know something about why the total mass has remained unchanged given this new discovery of galaxies.

This is basically a resolve the paradox question, so C) wouldn't work here because it doesn't help explain the paradox - namely, why, with the new evidence of more galaxies, does the universe's total mass remain unchanged?

Also, you mentioned that the new instruments could help explain the discrepancy although I'm not too sure how that could be. The new instruments just help discover more galaxies, but as you mentioned, it doesn't touch upon the question of why the universe's mass remains the same.

[KelliW299]

Please explain answer choice C more. If the instruments are better it allows us to see more galaxies. So those galaxies were already there we just SEE them now. So the same weight/mass was unaffected because they were already there we just couldn’t see them yet. Please clarify.

[ohthatpatrick]

You're using the idea "we SEE more than before", but neither the stimulus nor (C) says that we now see more than we used to.

The stimulus is talking about how many galaxies astronomers BELIEVE exist, and (C) is also talking about the number of galaxies that astronomers BELIEVE exist.

Astronomers BELIEVE a lot of things exist, even without having ever seen them (black holes .. Higgs boson ... etc.).

The paradox here is,
if they believed that 10 billion existed before,
and now they believe that 50 billion exist,
how come it hasn't really changed their estimate of the universe's mass?

Saying that they used to believe that 10 billion existed and that now they believe that 50 billion exist doesn't imply that they've SEEN any extra galaxies. And if we knew that they HAD seen more, it wouldn't imply that their estimate of how many exist had changed.

if the stimulus had said that
"Astronomers had previously been able to see 10 billion galaxies, but now they can see 50 billion. Nonetheless, their estimate for total mass is basically the same"

then we could have resolved that paradox by saying
"Astronomers don't estimate total mass based off what they can presently see, so even though they're seeing more it wouldn't change their estimate."

But this paragraph and choice (C) don't discuss astronomers being able to see more galaxies than before.