def back! by=simulation.step
      time = simulation.time - by
      simulation.recording.reconstruct( at: simulation.recording.floor( time ) )
        .tap { |sim| sim.run! upto: time }
    end
def back! by=simulation.step
      time = simulation.time - by
      simulation.recording.reconstruct( at: simulation.recording.floor( time ) )
        .tap { |sim| sim.run! upto: time }
    end
Steps the simulation back. This prototype version of the method simply
 reconstructs a new simulation at a given time (1 simulation step by
 default) before the current time.