The simulation
The world
Seasons, valleys and uplands, lakes, forests, herds, weather and illness: the physics Terrarium's people live inside.
The world is a grid of land with its own rules. It doesn’t care about the people on it, and nothing in it is arranged for them.
Land
Fertile land comes in patches: green valleys and lakeshores, with barren uplands between. The same layout gives the land its height: valleys lie low, uplands high. Climbing costs extra energy, and from high ground you see further.
Food grows on fertile land and is gathered by hand. Wood and fiber grow in stands that regrow slowly, fastest when half grown; an untouched meadow takes about a year to become forest. Thick forest is slow going and hides what lies beyond it. Stone lies in the uplands and doesn’t come back once quarried.
Water and wildlife
Lakes can’t be crossed. Their fish breed with the seasons and can be fished down. Game lives in herds that breed in spring and summer, wander between neighbouring cells, and drift onto poor land where they don’t do well. A hunt is likelier to succeed where herds are thick, and every kill leaves one fewer.
Seasons and weather
A year is 100 days: spring growth, summer plenty, an autumn that tails off, and a winter in which standing food dies back and almost nothing regrows. On top of the seasons come things no one can plan for: droughts that wither growth for weeks, and storms that batter shelters and anyone caught outside.
Bodies
Hunger rises every day, and food carried too long spoils; food kept in a storehouse doesn’t. Energy runs down with work and comes back with rest. Health falls to starvation, injury and illness, a fever that passes between neighbours and leaves survivors immune for a while. People are born, grow up in about fifteen days, can have children until about two thirds of the way through life, and live about four years at most.
Things people make
From what they gather, people craft tools (spears for hunting, axes for wood, poles for fishing) and build lean-tos, shelters and storehouses. Buildings take days of work, wear down and eventually collapse unless their owners keep at it.