interchangeable parts

[derek w]

If I have bricks that are black on 1 end and white on the other end,black on top and white on bottom,black on 1 face and white on other face.I can build 2 walls that are 2 layers thick,1 wall with all the black faces showing outward,and 1 wall with all the white faces showing outward.The black wall (I call a wall) the white wall (I call an anti-wall).The 2 walls are made of interchangeable parts.

If a photon with enough energy can produce an electron/positron pair,can I say that a photon is an interchangeable part(that it is both a photon and anti-photon at the same time ?)