Amazing physics hides behind many everyday things. felt for many years Hans Joachim Schlichting investigates these phenomena and explains them in his column to the readership of »Scientific Spectrum«. Schlichting is a professor of physics didactics and worked at the University of Münster until his retirement.
Although the sparkling areas give an impression of how badly the car’s paintwork has been marked by everyday life, you have to bear in mind that the actual number and length of the tiny scratches are much greater. A computer simulation illustrates this: For a random distribution of different scratches that are invisible in diffuse light, you can visualize the sections that come to light with a point light source placed vertically above them. The reflections then draw a pattern similar to that on a car roof and yet only reflect a fraction of all bumps.
© H. Joachim Schlichting (detail)
Modeled Quirks | A simple computer simulation shows only a few sections of the normally undetectable ridges (left) under a point light source (right).
Such radiating rings can also be seen, for example, as reflections on cutlery and other opaque objects, but also when looking through the plastic windows of an airplane. These are also exposed to mechanical influences. You can only see some of the tiny traces if you look through the window at a light source. In this case, the bright sections are not grouped around the mirror image, but around the original of the light source. Therefore, the physical conditions differ insofar as the light is not reflected at the scratches, but is refracted at them.
© H. Joachim Schlichting (detail)
Cutlery Reflexes | Under a light source, microscopic bumps on frequently used objects such as a spoon produce ring structures.
If you take a closer look, many grooves glitter colorfully. Apparently, some of the subtle irregularities are on the order of the wavelength of light. Then diffraction occurs, which breaks down the incident white light into the components of its spectrum. The structures act like fine slits along which the incident radiation front emits elementary waves in all possible directions.
If they overlap in the eye or on the camera chip, certain wavelengths are amplified or weakened according to the respective path differences. Depending on the observation position, the scratches often shimmer in such intense colors that they appear much wider than they really are.