PrepTest 132, Section 2, Question 20
Astronomer: Earlier estimates of the distances of certain(85 more words not shown)
Which one of the following,(33 more words not shown)
- AThe stars are(8 more words not shown)
- BThe younger the(11 more words not shown)
- CThe brighter a(6 more words not shown)
- DHow bright celestial(14 more words not shown)
- ENew telescopes allow(9 more words not shown)
Reading the argument
The stars can't be older than the universe they belong to. Something in the earlier estimates has to give. That doesn't by itself tell us whether the mistake concerns the stars' ages or the universe's age, and a new estimate isn't automatically right just because the old picture is impossible.
Still, follow the astronomer's proposed fix. The stars are farther away than previously thought. To look as bright as they do from that greater distance, they must produce more light than we thought. Think of a flashlight: a distant light needs to be stronger to look as bright as a nearer one.
How does being brighter make the stars younger?
What we’re looking for
That's the missing connection. The evidence revises distance and intrinsic brightness, but the claimed benefit concerns age. To help with stars previously estimated to be too old, the new brightness estimate needs to move their estimated age downward. The answer should tell us that brighter stars are younger.
Working the answers
- A
Being the oldest objects discovered doesn't connect the revised distance or brightness to a younger estimated age. The stars could be the oldest known objects under either estimate. We need to explain how the new information helps fix the inconsistency.
- B
This relates the age of the universe to how many bright stars it probably contains. Our question goes from the brightness of these particular stars to their ages. A claim about the universe's overall population of bright stars doesn't supply that connection.
- CCorrect
If brighter stars are younger, revising these stars' intrinsic brightness upward means revising their ages downward. The full chain is now clear: farther away than thought, therefore intrinsically brighter than thought, therefore younger than thought. That helps resolve the conflict created by estimating them as older than the universe.
The answer doesn't quantify the age change. It gives the direction needed to help resolve the problem, which is what the question asks.
- D
This concerns the relationship between distance and apparent brightness, which the argument already uses. It doesn't tell us anything about age. We still need the step from the revised intrinsic brightness to a younger estimate for these stars.
- E
Seeing a greater number of stars doesn't establish how old these particular stars are. Better telescopes could expand the catalog while leaving the original age conflict untouched. E adds information about observation without explaining the proposed correction.
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