What is U?

What is k? What is this mystery book you refer to? Why should I care? At least give us a title or author so we can look it up, because we can't make any sense out of your descriptions. You're pulling stuff out of thin air.

These are all simple problems with simple solutions, Einstein mass-energy equivalence has been around for almost a century. We know it works. What are you chasing here? What are you trying to tell us? Why are you complicating such a trivial problem?

This way of looking at the structure of mass indicates that the “mass” as we know it, is composed of three fundamental ingredients, one is space, which contains potential force and is the volume that movement can happen in, the second is the kinetic force which manifests itself as the density that is able to move in the space, and the third is the kinetic energy that causes the motion of the density within the space.
In other words, the symbol “u/k” in the formula indicates the structure of mass with its intrinsic space, density and motion. When such a combination is accelerated to the maximum speed then it will contain the maximum energy.

Johannes. That is just a bunch of fancy, scientific-sounding words that don't mean anything. It sounds like Scotty trying to explain how dilithium crystals work. Its gibberish.