Passage Summary: A scientist argues that because we don't live in a future where trillions of people have colonized the galaxy, that future probably won't happen, assuming we are typical examples of the human race.

Conclusion: It is highly unlikely that humans will ever colonize the galaxy on a massive scale.

Reasoning: If such colonization occurred, the vast majority of humans would exist during that era; since we are likely representative of humans and do not live in that era, the era likely will not exist.

Analysis: The scientist uses a probabilistic structure to reject a hypothesis. They start by identifying a necessary consequence of a theory—specifically, that if trillions of humans eventually exist, any random human (like us) would almost certainly be one of those trillions. By pointing out that we do not actually live in that time period, the scientist concludes that the initial theory of mass colonization is probably false. To identify this method, look for the move from a 'representative sample' premise to the rejection of a predicted outcome.