 Therefore, suitably configured billiard-ball computers may be used to perform any computational task.It is possible to simulate billiard-ball computers on several types of reversible cellular automaton, including block cellular automata and second-order cellular automata.In these simulations, the balls are only allowed to move at a constant speed in an axis-parallel direction, assumptions that in any case were already present in the use of the billiard ball model to simulate logic circuits.