"Edgar" wrote in message
...

No I haven't. You are confusing _into_ and _onto_.
Your beam of light only goes onto a square foot. Nothing can go into
something that only exists in two dimensions.



The concept of divergence (used in geometrical calculus) is a measure of any
type of flux crossing a surface as the enclosed volume goes to zero. As the
limit is taken, the enclosed volume shrinks to zero faster than the surface
area. The divergence is a measure of flux crossing a surface of zero
enclosed volume.

In the case of a beam of light entering an enclosed surface, the divergence
would be zero as the light source is external to the enclosed volume. The
total flux entering and leaving the surface (even if it is flat consider
both sides) is zero.

A sphere does exist in two dimensions, for instance in both angle and
radius. Only two dimensions needed to define the surface or volume. Not all
coordinate systems are cartesian or orthogonal.