Q20 - Astronomer: Earlier estimates of the distance

[giladedelman]

Thanks for posting!

You're right that this problem throws a lot of junk at us in order to obscure what would otherwise be pretty easy to spot. Let's start by identifying the core. The astronomer estimates that the stars are actually farther away, and therefore brighter, than previously thought. He concludes that these estimates help resolve the problem of having stars apparently older than the universe. So our core looks like this:

stars farther away and brighter --> not actually older than the universe

When we break it down like that, the assumption starts to jump out at us: he's got to be assuming that if stars are farther away or brighter (we can't be sure which is the important part), then they're also younger.

(C) is correct because it strengthens the argument by making that assumption explicit. If brighter stars are younger, then the new estimates do help resolve the discrepancy.

(A) is incorrect because whether they are the oldest doesn't help us conclude that they are actually younger than we thought.

(B) is incorrect because it doesn't tell us anything about the ages of the stars.

(D) is incorrect because it's all about brightness, and again, not at all about age.

(E) is likewise out of scope.

In fact, notice that all four wrong answers had nothing to do with the stars' age! It's interesting how much we can rule out if we at least have a clear understanding of the core. In this case, we could at least be sure that we needed an answer that tells us something about the stars' age.

Does that clear this one up for you?


#officialexplanation

[hwsitgoing]

Is there any way someone could walk me through this one. I'm having a hard time understanding the stimulus and answer choices. I think the whole distance part is throwing me off which now seems rather irrelevant to the argument. The mention of the universe in the final sentence made me look for it in the answer choice since it seemed like an unconnected concept.

Thank you!

[irene122]

Is there anyone confused by the question type of this question?

I used to think it is a resolve paradox question(from the stem), but concerning the stimulus--it more inclines to be a strengthen question?

[ohthatpatrick]

Great question, Irene.

I also saw the question stem as Resolve/Explain, so I was surprised to hear Gilad describing it as an argument. However, the stimulus in this case definitely does flow like an argument. The astronomer presents evidence that leads to a conclusion (prefaced by the conclusion cue "So").

The question stem is asking us which answer would explain how the astronomer's evidence justifies his conclusion, so that really is just a Strengthen question in the disguise of Resolve/Explain wording.

(It's extra disguised in the sense that the astronomer's conclusion actually uses the word "resolve")

Although "Resolve/Explain", "Resolve a Paradox", "Explain an Unexpected Result" are a bunch of different names to describe the same type of question, we could distinguish somewhat of a nuance between them:

'Explain' questions act a little more like Strengthen than 'Resolve' questions do.

Any mention of Resolving "a paradox" or "an apparent discrepancy" or something similar in the question stem means we should really read for
Idea 1 AND YET Idea 2?

The correct answer just needs to reconcile them / make them compatible, not necessarily prove one on the basis of the other. (normally, though, one of the ideas is more or less a given, and the second confusing idea is the one our answer choice explains)

Whereas if the question stem is asking us to "explain" something, then it may be easier to think of the thing to be explained as our conclusion and picture the answers more like Strengthen. In these questions, there is normally some piece of evidence to go off of, even if it's confusing as to how that evidence would explain the thing to be explained.

I hope I have somewhat Resolved the Apparent Discrepancy between Q20's question stem and its stimulus/answers. (Sorry, I couldn't resist)

[timsportschuetz]

On my initial read-through of this particular question I was similarly confused! On EXPLAIN THE PARADOX questions, you must find the answer that EXPLAINS THE UNEXPECTED RESULT(S) of the stimulus. Honestly, I was pressed for time at this point in the section and couldn't make much sense of the argument after my initial pass. Then, I started to attack the answer choices by eliminating clearly wrong ones (often, this method does not lead anywhere since the argument needs to be somewhat understood in order to eliminate answer choices - however, more often than not, on confusing questions like these, wrong answers should jump out at you. This is because test writers understand that the vast majority of test takers will experience similar confusion...).
A) Oldest yet discovered? Who cares... has nothing to do with the core. Eliminate.
B) This sounded attractive at first. Keep it for now.
C) Even better than (B). It mentions some of the key terms you should be looking for: "stars", "brightness", and "age". Keep for now.
D) Celestial objects? We are talking about STARS here... celestial objects could mean moons, nebulae, comets, etc... Eliminate.
E) Who cares... once again, completely out of scope. Eliminate.

This left me with (B) and (C). Then, I dug deeper and compared details of these answers in order to match to the stimulus. In (B), something odd jumped out at me: "the more bright stars...". Where in the original argument did I ever read about the relative quantity of stars in the universe???? Nowhere! Eliminate. I confidently chose answer (C), although I had virtually ZERO understanding of the original stimulus and did not want to waste time on a question that I knew I would most likely receive zero points for anyhow. However, after spending 45 seconds on eliminating obviously wrong answer choices using the above technique (which can be adopted to EVERY LSAT LR question...), I managed to actually earn a point that I initially thought impossible. Don't ever get panicked by confusing stimuli! Usually, the more confusing and complex the stimuli, the more the wrong answer choices will jump out at you! Use this general trend to your advantage.

[yeh.briann]

Is (D) wrong for the additional reason that the actual distance of the stars should be fixed, so in reality it wouldn't differ between when the earlier estimates were taken and when the astronomer made his estimates?

[bswise2]

Any additional insight with this question would be appreciated. Despite the thoughtful responses above, I think I am still missing something.

Below is my train of thought, so someone can point out to me where I am erring in my approach to the stimulus. I am definitely misinterpreting/overthinking something.

P1: Earlier estimates of the distances of certain stars from Earth indicate that these stars are about 1 billion years older than the universe, which is impossible.

P2: My estimates of the distances indicate that these starts are much farther away than previously thought.

Okay so, at this point the discrepancy is introducing itself. Early estimates indicate that the stars are too old, yet the astronomer is now asserting that they are farther/not too old. What changed between early estimates and the astronomer's estimate? My natural assumption is that the farther the star is, the less bright it is. It seems as though the astronomer is about to call that assumption out.

P3: The farther away the stars are, the greater their intrinsic brightness must be, given their appearance to us on Earth.

Okay so this must have been the change. The early estimates probably weren't educated with this new fact, so they were off in their distance estimates.

C: So the new estimates of these stars' distances from Earth help resolve the earlier conflict between the ages of these stars and the age of the universe.

Okay so the stimulus draws a correlation between brightness and distance, and then infers from that that the age discrepancy is therefore resolved. In order for this to be the case, we need an answer choice that creates a correlation between age and distance.

I was able to select C because it was the only answer choice that directly had to do with the stars' age, but I am confused because C draws a correlation between brightness and age. We don't need that correlation...we need a correlation between age and distance. I have learned from much LR practice that if there is an established correlation between A and B, as well as a correlation between B and C, that does not necessarily entail a correlation between A and C. Likewise, we have a correlation between brightness and distance, C gives us a correlation between brightness and age, so how then can we infer the needed correlation between distance and age?

Thanks in advance.

[ohthatpatrick]

You're correct that there can be a correlation between A and B, and a correlation between B and C, but NOT a correlation between A and C.

But we're not talking about correlations here (inert statistical coincidence). We're talking about ACTIVE relationships!

When you say "the brighter it is, the younger it is", those variables move in tandem.

If a star is brighter than we thought it was, then it's younger than we thought it was.
If a star is dimmer than we thought it was, then it's older than we thought it was.

We are also given "the farther it is , the brighter it is".
So if a star is farther than we thought it was, then it's brighter then we thought it was, so it's younger than we thought it was

It's still technically accurate to call these two "dependent relationships" correlations,
just as it's technically accurate to call a "square" a rectangle.

Any two variables that have some dependent relationship will be correlated,
but it's not true that any two things correlated have a dependent relationship.

Just as every square is a rectangle, but not every rectangle is a square.

I have no idea if "dependent relationship" is an accurate math term, by the way, but what we're referring to is a relationship in which you say
The more X, the more Y
or even
The more X, the less Y

These do NOT have exceptions, as normal LSAT correlations would.

A normal LSAT correlation would be something like "people who take advanced math tend to have higher GPAs than those who don't", but that doesn't mean that EVERY SINGLE person who takes advanced math has a higher GPA, nor does it mean that "the more advanced math you take, the higher your GPA".

[bswise2]

But we're not talking about correlations here (inert statistical coincidence). We're talking about ACTIVE relationships!

When you say "the brighter it is, the younger it is", those variables move in tandem.

Yes! This is exactly what I needed to understand. The relationship between brightness and distance is "stricter" than a general correlation, so, in light of C (another "strict" relationship), this does work. Thank you.