This animation shows a simulation of a shock wave moving through a gas and pushing cylinders. Eventually the shock wave reflects off the wall at the right and hits the cylinders again. The simulation also generates reflected shocks, with colors showing different gas densities. “Cool” colors such as blue correspond to low densities, while “hot” colors such as red and pink depict high densities. The computer represents density as values located at approximately 1 million discrete “grid points” distributed throughout the space being modeled. The number and position of these discrete values changes over time. The black boxes show grid boundaries, which are sub-regions in the space being modeled where grid points are moving or where the number of points has been increased to obtain a more accurate answer.