  The derivation becomes possible when we find a new formalism which connects
the relativistic mechanics with the quantum mechanics. In this paper, we
explore the quantum wave nature from the Newtonian mechanics by using a
concept: velocity field. At first, we rewrite the relativistic Newton's second
law as a field equation in terms of the velocity field, which directly reveals
a new relationship connecting to the quantum mechanics. Next, we show that the
Dirac equation can be derived from the field equation in a rigorous and
consistent manner.
