The following basic notions are used throughout this documentation.


All matter in alien is made up of cells. One can think of them as a kind of smart particles. They have physical properties such as

  • a position in space
  • a velocity
  • an internal energy
  • bonds to other cells

as well as metadata (color and annotation) and additional functions, which can be triggered by an other entity named token.

Cell cluster

A cell cluster (or cluster for short) is a network of cells. Two cells in a cluster are therefore connected to each other directly or via other cells. A cluster physically represents a rigid body with a center position, velocity and angular velocity. In a simulation, two clusters can merge (make connections between some of their cells) if they collide with a high velocity. Conversely, clusters can also be damaged (loss of cells). We will sometimes refer to cell clusters as bodies or agents.

Cell function

Each cell has a special function which is executed when a token passes it. Some important functions are

  • computer: The cell contains a small program that is executed on it. The program can access both the memory of the cell and the token.
  • constructor:  Enables the construction of a new nearby cell while consuming internal energy.
  • weapon: Steals internal energy from nearby cells of other clusters.

There are many other functions such as propulsions, scanners, communicators and sensors.

Energy Particle

An energy particle is a particle which has only one energy value, position and velocity. Unlike cells, they cannot form clusters or perform any additional functions. Energy particles are produced by cells as radiation or during decay, and in turn can also be absorbed.


A token moves from cell to cell within a cluster and coordinates the execution of cell functions. After a next time step, three possibilities can occur:

  • The token disappears if no matching connected cell is found.
  • It can move to a connected cell if there is a matching connected cell.
  • It can fork and move to multiple connected cells if more than one connected cell fits.

A token possesses an internal energy and has an own memory.

Active cell cluster

This is a cell cluster that has at least one token. We will sometimes refer to active cell clusters as machines.


A collection is a set of clusters of cells or particles.

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