PrepTest 158, Section 3, Question 21
Professor: Many scientists hypothesize that there is an(54 more words not shown)
Which one of the following(8 more words not shown)
- AThe low visibility(29 more words not shown)
- BThe hypothesis of(23 more words not shown)
- CA hypothesis is(25 more words not shown)
- DMost scientists who(11 more words not shown)
- EThe general theory(18 more words not shown)
Reading the argument
An invisible medium could explain why other star systems are hard to see. Is that the only possible explanation?
The professor says we already have another account: general relativity completely explains the low visibility. I can see the response to the scientists. If an existing theory handles the observation, we don't automatically need to add a new light-absorbing medium to explain it.
What we’re looking for
My first question is whether the theory we're relying on is correct. If that explanation failed, the professor couldn't simply use it to dismiss the proposed medium. For the necessary-assumption question, that's the direction I'd initially investigate. But keep the conclusion precise: the professor says there is no reason to believe the hypothesis, not that the hypothesis has been proved false. Let's see what the argument needs in order to make that dismissal.
Working the answers
- A
The professor doesn't need to deny that a light-absorbing medium could explain the low visibility. The response is that an existing theory already explains it. Two accounts could each explain an observation; saying one is unnecessary doesn't require saying it would be incapable of explaining anything.
- B
This makes explaining the low visibility a requirement for the medium hypothesis to be correct. The professor doesn't lay down that rule. The argument concerns whether this observation supplies a reason to accept the hypothesis when another explanation is already available. B doesn't establish the relationship between the competing accounts.
- C
This proposes a rule for accepting a hypothesis when it explains something existing theories cannot explain. But the professor says the observation here is already completely explained. That is the opposite situation. We don't need C's general rule about otherwise unexplained phenomena to make this argument.
- D
Scientists could accept general relativity and still propose a medium, or reject relativity and propose one. Their acceptance doesn't determine whether the professor can use relativity in the way the argument does. Counting their beliefs supplies no necessary connection between the explanations.
- ECorrect
This finds a different issue from my initial concern about relativity's accuracy. What if relativity's explanation itself depends on the light-absorbing medium? Then invoking that explanation wouldn't give us an independent reason to dismiss belief in the medium. It would rely on the very thing the professor wants to set aside.
Imagine being told, “We don't need to believe in this component because our existing account explains everything,” and discovering that the existing account needs the component to work. That response falls apart. The professor must assume that relativity does not depend on the medium hypothesis.
E doesn't require the two theories to have nothing in common. It rules out the particular dependency that would undermine using one to dismiss the need for the other.
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