Physicists don't typically think of initial conditions right after the Big Bang in the way you're suggesting.
The typical assumption is that the very early universe was in thermal equilibrium, in which case the set of particles present at any given time depends only on the temperature, and not on initial conditions.
That the photon is only one of several particles, so you need to explain how it transforms into the others, or why any of the others isn't the first one instead:
https://upload.wikimedia.org/wikipedia/commons/0/00/Standard...