The absolute necessity for the continuation of life without any doubt is food stuff. This comes in the forms of solids, liquids, and gases. The only end product is a form of physical energy called heat. Heat is studied under a branch of classical physics called thermodynamics. Later, it was extended into statistical mechanics and then into quantum mechanics where and when the form of energy was quantized. Wherever and whenever this quantization was described by the special theory of relativity, Dirac discovered a mysterious form of negative energy. Since energy must always be positive, he theorized the existence of antiparticles and consequently he combined special relativity and the old quantum mechanics into a relativistic quantum mechanics called quantum electrodynamics (QED) and led him to discover the existence of quantized spin for all elementary particles. This theory also made extremely accurate calculations of the magnetic moments of elementary particles that agree with experiments to hundreds of decimal places.

However, for all these to make any sense, the form of the relativistic energy equation must necessarily describe a form of square of energy: E=pc+mc where p is the linear momentum, m is the rest mass, and c is the constant known as the vacuum speed of light or vacuum speed of all forms of electromagnetic waves. These discussions suggest the inevitable fact that the true absolute necessity of the physical universe is really a form of square of energy.