In a normally busy school at night, why can silence itself feel like a warning?

Answer: Expected social noise vanished

Expected social noise vanished ✓ — Right. In a social building, ordinary noise is information: people nearby, normal use, help available, nothing has interrupted the routine. When that soundscape disappears, the brain has to explain an absence, which can feel like uncertain threat. Studies of public spaces even find ambient sound can raise perceived social presence, so silence removes a safety cue rather than simply adding quiet.

Silence hides approaching steps — Plausible, because in a silent hallway you may start listening for footsteps. But the warning feeling begins before any approaching sound appears. The stronger mechanism is missing normal social audio: a place designed around voices and routine suddenly stops giving those safety cues.

Darkness sharpens hearing — Not quite. Darkness can make people listen harder, but the interesting part is that the same quiet room feels different after-hours than during a library exam. Context changes the meaning of silence. In a school, the missing crowd is the message.