Curiosity, with a slider.
WhatIfWorlds is a growing set of simulations where you change the rules and watch a system answer. The aim is that you finish a session able to say why something happened, not only that it did.
Every simulation runs in your browser. There is no account, no database and no server doing the calculation, so what you try stays on your device.
What the models leave out
A model is useful because it is smaller than the world. The traffic ring has one lane, identical buses and no overtaking. The orbit has one planet. The meadow has two species. Each page says what the model shows well, and where to be careful about stretching it.
The mathematics is real, and credited here, but the numbers are illustrative. Do not plan a motorway with them.
Where the models come from
- Traffic Ring: the Intelligent Driver Model by Treiber, Hennecke and Helbing (2000), on a closed loop like the ring-road experiment by Sugiyama and colleagues (2008).
- Orbit Lab: Newtonian gravity, integrated with the velocity Verlet method, which keeps closed orbits from drifting.
- Predators & Prey: an agent-based model: every hare and fox is simulated individually, with grass that regrows, energy, breeding and hunting. The classic Lotka–Volterra equations describe the same kind of cycle in aggregate.