When an ocean wave hits a beach, the swashing action pushes grains of sand up and pulls them down. The shape of the beach (as observable in any given moment) is

When an ocean wave hits a beach, the swashing action pushes grains of sand up and pulls them down. The shape of the beach (as observable in any given moment) is steady relative to a number of waves and governed by cumulative averages of their features, but will change as the direction of waves, tide, current, etc. shifts over time. A beach with finer sand but similar wave action and angle will have a different incline from one with coarser sand or pebbles. I am optimistic, as is the article, that further research into variations in metal, light, angle of incidence, and time will lead to a better understanding of the parameters of this backwards electron motion effect, of the nature of light and electromagnetic waves, and moreover, the substrate/matrix in which both are active, perhaps even of dark matter and a moving-zero mass.