Every simulation here is an example of a few much bigger ideas. Read one, then go and watch it happen.
When a change feeds back into its own cause, small pushes get amplified or damped. A driver braking makes the driver behind brake. Predators eating prey reduces the food for more predators. Most of the surprising behaviour in these simulations comes from feedback.
See it in Predators & PreyNo bus is programmed to make a jam. Each follows one rule about the bus ahead. The jam appears from their interaction, and it can move in a different direction from every single bus.
See it in Traffic RingA system can sit in balance and still be fragile. A pencil standing on its tip is balanced. So is a meadow of predators and prey, until you change the food. Whether a nudge fades or grows is the difference between the two.
See it in Predators & PreySome quantities cannot be created or destroyed, only traded. A planet trades speed for height as it swings out and back in, and the total stays the same. Spotting what is conserved is one of the quickest ways to understand a system.
See it inEach simulation page also explains its model, suggests experiments and compares scenarios. The short versions:
Traffic Ring
Each driver in this model only watches the bus directly ahead. Too close, and they brake. Plenty of room, and they speed up toward their target speed. That is the whole rule set. Nobody is slow on purpose and nobody is breaking anything.
Phantom Jam
Every driver here follows one rule: keep a gap to the car in front. When that gap shrinks, brake. When it opens, speed up. Nobody is slow on purpose and nothing blocks the road.
Green Light
When the light changes, only the first driver can see an empty road. The second looks at the first car, waits for it to move, reacts, and pulls away. The third does the same with the second. Each small delay is only a second or so, but a queue of twelve cars adds twelve of them. Engineers call the time the first few cars lose this way the start-up lost time, and treat it as about 2 seconds [1].
Predators & Prey
Rabbits graze in loose herds. They stay near each other, follow the group, and keep a little space. A fright spreads from one rabbit to the next. A rabbit that spots a fox bolts for the middle of the herd, sidestepping as it runs, until it tires. Foxes search where rabbits are thick, creep up on ones that have not noticed them, then sprint, aiming ahead of the rabbit and coming in from the side when a partner is already chasing. They pick off the young, the weak and the stragglers, give up when they run out of breath, and rest after a meal.
How Rumours Travel
This is a small town of named people, living in six districts. Bigger faces have more friends. One person hears something. Each day, everyone who is telling tries each of their friends, and each friend who hears it may repeat it or keep it to themselves. Tellers lose interest as the days go by.
How Smoking Hooks the Brain
This is one person, followed day by day. At the top left is the person and a bar for how much they want a cigarette. Below is a clock of the day, with the moments that get tied to smoking: coffee, stress, meals, a break, evenings out. On the right is a close-up of the brain. The chart at the bottom shows the nicotine in the blood, the craving, and how hooked they are.
Collision Lab
When two things hit, each pushes on the other with the same force for the same time, in opposite directions. So whatever momentum one gains, the other loses. Momentum is mass times velocity, added up with direction, and the total stays exactly the same unless something outside, such as a wall, pushes too.
Inflation
This is one street. Dana runs the bakery and sets prices. Marcus works in a factory and asks for raises. Priya has $10,000 in the bank. Sam rents a flat. A central bank sets the interest rate. One second is one month, and the faces show who is coping: a green ring is fine, red is being squeezed.