# Tilt: Controlling (masses) of tiny passive agents by external forces.

Let us go very small, cell size level for medical applications. This size currently is out of reach for swarm robotics (a fundamental problem is that energy capacity decreases faster than e.g. the resistance). A different approach is to use passive agents that are propelled by external forces as such as controlled magnetic fields of an MRI scanner. This introduces a significant difference to classical swarm robotics since now all agents move uniformly and the only individual control is by collisions that stop a part of the agents from moving.

We now consider some possible problems, starting with the following: You are given a set of agents in an unknown environment and want to explore it with as few commands as possible. You always now the positions of the agents and can sense collisions with obstacles (by a failed movement). Such a scenario can be in medial imaging with too low contrasts for classical techniques and an application of a contrast medium is contraindicated. Try it yourself!

A related problem is the question, how to get as many agents inside as possible.