E = mc^2 is just a beginning. OK, lets consider some of the questions that come to mind. When looking at E=mc^2. It is obvious that it does link energy to mass, and you say that the “thing” can change from energy to mass and back again, so, lets say that energy changes to mass, the question is; is there part of that energy still within that mass, or has all of the energy turned into mass and how did that transformation occur. Or to put the question differently; why does mass behave the way it does and why does energy behave the way it does?

You are saying that photons do not accelerate or decelerate, then what happens to the photon when it is absorbed by the electron orbit of an atom?
When an electron orbit returns to the non-excited state, there is a photon that is emitted from that location; the question then is: Was the photon travelling at the light speed while in the atom, or if it was created at that moment did it achieve its speed instantly?

What is the difference between hypothesis and speculation?

As for the book; metaphorically speaking: You have already thrown that into the trash pile.