object limits

where is the limit of an object?
is it the boundary of its form?
is it the shadow it casts?
is it an experience of the object?
is it those uninterrupted quanta of light that escape our solar system?

this question really only tests what we might mean by 'limit' but studying the idea of boundary, periphery and edge - as much as object and presence et al - has a hints at something of importance to my thoughts on architecture right now.

in asking questions of 'limit', i have a clue that it may be useful to begin by searching for the essence of a thing