Light and Shadow – The Experimental Collaboration Between Ernst Mach and Ludwig Mach, Father and Son
Only few subjects in physics are as affecting as the lessons of light. Through the human visual faculty, light directly connects to the sensations. Its properties are possibly therefore among the oldest areas of study in the natural sciences. However, in contrast to the objects that convey the laws of mechanics to human understanding, the carrier of light seems immaterial and therefore impalpable. Hence, the more strange some of the optical phenomena appear at first sight, as they do not tie to intuition and only can be apprehended by adopting a wave model for the study of light. The phenomenon of interference, i.e. the superposition of waves upon their coalition, is a particular striking example in this category. It is only through the image of waves that one can understand why at the union of light ray with another light ray, their result not only shows brightness but also darkness.