Energy is a measurement of the ability to work, rather than a substance. The amount of energy a volume of mass has is mass times the speed of light squared. Hence E=M(c²).
An example is nuclear fission. When mass undergoes fission it splits some of the mass into fission products that radiate and that is 'energy'. Mass has simply changed some of its form and location in the Higgs field in space-time. It lost part of its original mass in the process. I don't know how efficient atomic fission is at converting mass like plutonium yet I gather it isn't 100%.
Science hasn't found the most basic quanta. Quarks are made of gluons. String theory is just a theory. Maybe they use the infinite dimensions of Hilbert Space to find math formula that support one-dimension strings in four dimensions.
A problem is that massless particles pick up a third dimension slowing, entangled in the Higgs Field. Did primary massless two dimensional particles appear after becoming entangled in an unknown field?
Another question is how massless particles are ever subject to gravity and if not why they should have been bound to a singularity.
