  The Standard Model is an up-to-date theory that best summarizes current
knowledge in particle physics. Although some problems still remain open, it
represents the leading model which all physicists refer to. One of the pillars
which underpin the Standard Model is represented by the Lorentz invariance of
the equations that form its backbone. These equations made it possible to
predict the existence of particles and phenomena that experimental physics had
not yet been able to detect. The first hint of formulating a fundamental theory
of particles can be found in the 1932 Majorana equation, formulated when
electrons and protons were the only known particles. Today we know that parts
of the hypotheses set by Majorana were not correct, but his equation hid
concepts that are found in the Standard Model. In this study, the Majorana
equation is revisited and solved for free particles. The time-like, light-like
and space-like solutions, represented by infinite-component wave functions, are
discussed. Furthermore, by introducing subsidiary conditions on the mass term,
it is possible to quantize both the fermionic and the bosonic towers, obtaining
the mass spectrum of the entire family of charged leptons, baryons and mesons.
