Once it seemed that light had energy but no mass and matter had mass but no energy, until Einstein found that light had relativistic mass and matter had a resting energy that could be released in nuclear bombs. It became apparent that mass and energy were somehow related.
Mass was originally defined as weight which was later refined to be gravitational mass. Newton’s discovery that a mass needed a force to accelerate it led to the definition of inertial mass. They are different because a weightless object in space still needs a force to move it, so it has inertial mass although it has no gravitational mass. If momentum is defined as mass times velocity, a massless photon should have no momentum but solar sails move when the sun shines on them and photons are bent by the gravity of the sun. This led to another revision as a photon with no rest mass was said to gain relativistic mass as it moves to give it momentum.
Light was once seen as pure energy where Planck’s relation defined a photon’s energy E as its frequency f multiplied by Planck’s constant h, so E = hf. The last chapter defined energy as the processing rate at the node, so it reduces as the wavelength increases because as more nodes share the process, the processing per node reduces. Equally as frequency increases, wavelength decreases, so fewer nodes running the same process each process faster, giving more energy.
Einstein’s equation E=mc2 does for matter what Planck did for light, define its energy. In 1905 he deduced that the energy of matter is its mass times the speed of light squared and atom bombs confirmed this but it has never been clear why mass relates to light at all. If mass is an inherent substance, why does its energy refer to the speed of light?
If an electron is extreme photons repeatedly colliding in many node channels, the inherent energy of matter relates to the energy of those photons. Each channel contains the equivalent of a photon with a one node wavelength, whose energy by Planck’s relation is Planck’s constant times the speed of light divided by one Planck length. If Planck’s constant is one quantum process transferred over a Planck length squared per Planck time, substituting for Planck’s constant in Planck’s relation gives Einstein’s equation for mass and energy (Note 1).
Quantum realism derives Einstein’s equation from the conclusion that matter is made of extreme light repeatedly colliding.
Note 1. In this model, the speed of light c=LP/TP, for LP Planck length and TP Planck time. A photon’s energy EP=hP.c/l, for hP the energy of one quantum process transfer, c the speed of light and l the wavelength. In an electron l is one node, so EP=hP.c/LP. If mass m is the program that repeats, h transfers m over a Planck length square every cycle, i.e. hP=mp.LP.LP/TP. Substituting gives EP= mp.LP.c/TP, or EP=m.c2. This derivation doesn’t prove E=mc2. Einstein did that based on how our physical world behaves. It just finds this model consistent with Einstein’s equation.