They've found that a simulation of particular effect is exponential is the number of particles participating. Thus, concluding it will be impossible to simulate a large number of such particles. But, Quantum computers in theory can work with exponential time: https://cs.stackexchange.com/questions/12892/quantum-computers-parallel-computing-and-exponential-time Thus, if our simulators have access to those computers, they can simulate those kind of interaction in linear time.