Researchers trained language models on text from before 1930 to create AI that genuinely doesn't know what happened after that year, then had people interact with these "historical minds" to test whether it changes how they view the past. A preregistered experiment with 240 participants found that talking to a pre-1930 AI reduced people's tendency to think the past was more moral than the present.

• The core innovation is using temporal knowledge cutoffs as an experimental variable—training LLMs on historical corpora so they can authentically respond without knowledge of subsequent events, making the past interactable in ways archives and living testimony cannot.
• A randomized controlled trial showed interaction with a pre-1930 model significantly reduced the "illusion of moral decline," a cognitive bias where people perceive historical periods as more ethical than the present.
• This opens a new methodology called "science fiction science"—turning speculative thought experiments into testable empirical studies by using AI as a tool to reconstruct historical perspectives.

Researchers built an experiment where people interacted with an AI trained only on pre-1930 text to see if talking to a "historical mind" would shift their views about the past. It worked—people who chatted with the old-data model reported less of a bias that the past was more moral than today, compared to those using a current AI.

• The experiment reduced the "illusion of moral decline"—a documented bias where people assume past societies were more ethical than they actually were—by having participants interact with a historically-bounded language model instead of a contemporary one.
• Historically-bounded LLMs create an experimentally accessible way to approximate talking to someone from the past without modern knowledge contaminating their perspective, solving a real methodological problem in behavioral research.
• This framework treats AI systems as research instruments that can deliberately manipulate interaction conditions (in this case, temporal knowledge) to study and influence how people perceive, reason, and reflect.