PrepTest 134

Correct. Argument or Facts:
Facts

Question Type:
Paradox

Stimulus Summary:
Astronomers now believe that there are 40b more galaxies than they used to, but they also believe that the total mass of the universe is about the same.

Answer Anticipation:
Don't get lost in all the science here! At its heart, this paradox boils down to a simple question—how could astronomers believe there are 5x as many galaxies as before, but also believe they wouldn't add much to the total mass of the universe?

There are two potential explanations for this.

First, it could be the case that the astronomers believe that each galaxy is much less massive than they previously thought. It's possible that before they were "lumping together" multiple galaxies, or telescopes prevented distinguishing close-together galaxies from each other.

Second, it could be that galaxies, overall, aren't all that massive compared to other stuff in the universe. If galaxies only account for .1% of all mass in the universe, then 5x as many galaxies would only account for ~.5% of all mass in the universe—and the total wouldn't go up all that much.

Answer Explanation:
This answer goes with our second explanation. If the galaxies only make up a "tiny" percentage of the total mass of the universe, that total wouldn't go up when estimates of the total number of galaxies only goes up 5x.

Key Takeaway:
It's easy to get lost in science or math when the content of a question is difficult. However, most science questions focus on change, so you should focus on what changed and don't get distracted by anything else.

Incorrect. A rough estimation should still allow a rough estimation of the total mass of the universe—which would be assumed to increase if 40b more galaxies were estimated!

Incorrect. This answer might explain how astronomers went from 10b galaxies to 50b, but it doesn't explain why that didn't add to the total mass of the universe.

Incorrect. The paradox surrounds the total number of galaxies in the universe, not how they were formed, so this answer is out of scope.

Incorrect. Different procedures could still yield the same result, and even if there are different results, presumably they would all increase to some degree if 40b more galaxies were discovered. This answer might call the exact number of the mass of the universe into question, but it doesn't explain why it didn't go up when evidence of more galaxies was uncovered.