Not sure if this should be in the physics section or here in philosophy. I think the topic may fit in both domains. What has lead me to inquire about this particular effect is the description of it as given on Wikipedia. I wonder if what I am reading is an accurate description of the circumstances or if there is an aspect or two of it that I am not able to comprehend. Here it is:
The 3D illusion mirror effect is produced whenever there are two parallel reflective surfaces which can bounce a beam of light back and forth an indefinite (theoretically infinite) number of times. The reflections appear to recede into the distance because the light actually is traversing the distance it appears to be traveling.
For example, in a two-centimeter-thick infinity mirror, with the light sources halfway between, light from the source initially travels one centimeter. The first reflection travels one centimeter to the rear mirror and then two centimeters to, and through the front mirror, a total of three centimeters. The second reflection travels two centimeters from front mirror to back mirror, and again two centimeters from the back mirror to, and through the front mirror, totaling four centimeters, plus the first reflection (three centimeters) making the second reflection seven centimeters away from the front mirror.
Each successive reflection adds four more centimeters to the total (the third reflection appears 11 centimeters deep, fourth 15 centimeters deep, and so on). Each additional reflection adds length to the path the light must travel before exiting the mirror and reaching the viewer. Each reflection and the additional distance traveled by the light reduces the brightness of the image, which also fades into the distance.
I suppose what I take from this description, in sum, is that there is a distance that light ("photons") is indeed traversing in the form of a reflection that is cast between two mirrors. When I think of "distance" I think of something that I or another object is capable of traversing, e.g. Walking from Point A to Point B. However, this kind of "distance" that is being alluded to in the article is not one that I nor any object are capable of traversing...not at least without shattering the mirror into pieces.
This effect can only occur via visual-photo transduction so without an observer it is not something that could happen on its own. Like a mirage. According to the description given what is being assessed is not an "illusion of distance" and if it were it would be the first one, that I know of at least, that can be measured in centimeters.
How is light capable of traversing a distance between two mirrors that lack the depth necessary for anything to travel through in such a way that the effect is being measured (as though there is a depth of some sort)? How am I to interpret the meaning of "distance" in this scenario?