Logical Reasoning

PT134 · S3 · Q13 Astronomers have found new

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Astronomers have found new evidence that the number of galaxies in the universe is not 10 billion, as previously believed, but 50 billion.

Apparent Paradox

Astronomers have found new evidence that the number of galaxies in the universe is not 10 billion, as previously believed, but 50 billion.

This discovery will have an important effect on theories about how galaxies are formed.

But even though astronomers now believe 40 billion more galaxies exist, many astronomers’ estimates of the universe’s total mass remain virtually unchanged.

Evaluate

How could it be that five times as many galaxies as were once thought to exist would not correspondingly increase the estimates of the universe’s total mass? This might be the case if the astronomers were to decrease the estimated amount of mass contained within each galaxy.

13.

Which one of the following, if true, does most to explain why the estimates remain virtually unchanged?

  1. Correct

    The mass of galaxies is

    Why this is right

    This is another way to increase the mass contained within galaxies and yet not have it significantly increase the estimate of the mass of the universe. Simply put, multiplying the number of galaxies would have little impact on the mass of the universe if galaxies were a relatively small percentage of the total mass of the universe.

    Skill tested: Paradox · how this choice captures the argument's function is the move to repeat next time.

    79% picked this

  2. The overwhelming majority of galaxies

    Too Weak

    That the estimates are rough approximations does not explain why multiplying the number of galaxies by a factor of five did not significantly increase the estimate of the mass of the universe.

    3% picked this

  3. The number of galaxies that

    Half Scope

    This may explain why the estimate of the number of galaxies increased, but it does not explain why the estimate of the mass of the universe did not also significantly increase.

    3% picked this

  4. Theories about how galaxies are

    Reversal

    This reverses the causal relationship. It should be that estimates of the universe’s total mass are rarely affected by theories about how galaxies are formed. Even this, however, does not explain why it is not affected.

    11% picked this

  5. There is no consensus among

    Applies to Both

    This would apply both before the estimated number of galaxies was increased and after, so it cannot explain the difference.

    5% picked this

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