What can a pixel reveal to a designer? In short, nothing. A pixel is a vacuum. At rest, a pixel cannot be touched, heard, seen or smelled. It has no purpose, other than to do what it is told to do. It requires something — or someone — to describe what it should be before it is observed. – Rob Rhyne

Spot on. His article makes a comparison between the physicality of materials and the lack thereof within pixels.
And I learned a new word: caustics