PrepTest 159 - Section 2 - Passage 3 - Question 21

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Since 1929, cosmologists have known that the universe is expanding. █████ █████████ ████ ███████ ████ ███ █████████ ██ ███████ ██ ███ ██████████ ███ ███████ ████ ███████ ███ ██ ███ ████ ██████ ███████████ ███ ███ ██ ███████ ███ ███████ ██ █████████ ███ █████████ ██ █████████ █████ █████ ██ ███████████ ██ █████ █████████ ███ ████████ ██████████ ████ ████ ████ ███████ ████ █████████ █████ ████████ █████ ████ ███ █████████ ██ ███ ████████ ██ ████████ █████████████

Unexpected phenomenon · Expansion of universe is accelerating, rather than slowing down

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Two potential explanations · Both challenge current understanding of the universe

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Explanation 1 · Dark energy

The idea of energy stretching space dates back to Einstein. There’s some support for this theory.

Potential origin of dark energy · Created by “virtual” particles

The particles pop in and out of existence, creating “vacuum” energy.

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Inconsistent evidence · “Vacuum” energy theory of dark energy not supported

Explanation 2 · Gravity doesn’t work as predicted across large distances

Additional details about Explanation 2 · Theory is radical and might be easier to test than dark energy theory

Passage Style

Phenomenon-hypothesis (RC)

21.

Which one of the following, ██ █████ █████ ████ ███ ████ ███████ ██ ███ █████ ██████ ██ ███ ███████████ █████████ ██ ███ ████████ █████████ ██ ███ ████████

Question Type

WSE (RC)

We're trying to strengthen the first theory, which posits that dark energy explains the accelerated expansion of the universe. It's not clear what we can anticipate before going to the answers. Perhaps the correct answer might help resolve the discrepancy mentioned at the end of the third paragraph. However, that discrepancy relates only to one specific version of the dark energy theory (the version attributing dark energy to virtual particles and vacuum energy). It's possible the correct answer may strengthen the dark energy theory more generally without relating to the specific version described in the third paragraph. Let's keep an open mind.

Something like Einstein's ████████████ ████████ ██ █████████ ██ ████ █████ ██ █ ████ █████ ██ █████ ████████████ ██████████

This answer is the one that most lends support to the dark energy theory. We know that the idea of an energy that exerts pressure on the universe was proposed by Einstein in 1917. If Einstein is wrong about the existence of this pressure, then that would undermine the idea of dark energy, which is a kind of energy alleged to exert pressure on the universe. But if Einstein is right about the existence of this pressure, then that helps the dark energy theory by at least establishing the baseline assumption that there is some kind of pressure exerted on the universe. (A) provides evidence tending to support the idea that there is a source of pressure on the universe. If we need something like the cosmological constant to make sense of many other phenomena, that suggests the kind of pressure described by Einstein's cosmological constant exists.

40%

Quantum mechanics reveals ████ ███ ████████ ███████ ██ ███ ██████ ██████ ███ █████████ ██ ███ ███████ ██ ████████

This provides evidence against the idea that vacuum energy constitutes the dark energy that applies pressure to the universe. So it doesn't support the dark energy explanation of the universe's expansion.

17%

Virtual particles exist ███ ████ █ █████ ████ ████ ████ ██████ ████████ ██ ███ ███ ████ ██████████ ██████████

It's not clear that virtual particles need to interact with nonvirtual particles in order for the virtual-particle-based version of dark energy theory to work. In any case, if (C) does anything, it might suggest that virtual particles aren't the origin of dark energy.

10%

Observations of distant ████████ ████ ████ ███ ████████ ████ █████ ███████ ██ ███ ████████ ████ ████ ████ ████ █████ ██ ████████ ████████████ ██ █████ ████████ ████ ███ ████████

It's not clear how the relationship between distance and velocity of movements relates to the dark energy theory. The explanation that involves gravity is the second theory described in the last paragraph, not dark energy theory.

27%

Recent studies of ███ █████████ ██ ███ ███ ████ ████ █████ ██ ███ ████████████ ██ ██████████ ███████ ██████ ██ ███████████

It's not clear how the theory of relativity relates to the dark energy theory. The explanation that involves the theory of relativity is the second theory described in the last paragraph, not dark energy theory. (Note that the cosmological constant mentioned in connection with the dark energy theory is different from the theory of relativity mentioned in the last paragraph.)

PrepTest 159 - Section 2 - Passage 3 - Question 21

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