1. An apparatus for computing particle interactions, said apparatus comprising a plurality of computation nodes and a first communication system, wherein said first communication system and said computation nodes collectively define a parallel processing system, wherein said first communication system comprises links interconnecting the computation nodes, wherein said computation nodes are arranged according to a geometric partitioning of a simulation volume, wherein each of said computation nodes comprises storage, a plurality of processor subsystems, and a second communication system, wherein said storage stores particle data, wherein said particle data is associated with particles in a region of the geometrically partitioned simulation volume, wherein each of said processor subsystems performs a different computational task, wherein each of said processor subsystems comprises a processor, wherein said second communication subsystem interconnects said processor subsystems and said storage, and wherein the processor subsystems of the computation nodes together coordinate computation of the particle interactions in a distributed manner.