  When Einstein formulated his special relativity in 1905, he established the
law of Lorentz transformations for point particles. It is now known that
particles have internal space-time structures. Particles, such as photons and
electrons, have spin variables. Protons and other hadrons are regarded as bound
states of more fundamental particles called quarks which have their internal
variables. It is still one of the most outstanding problems whether these
internal space-time variables are transformed according to Einstein's law of
Lorentz transformations. It is noted that Wigner, Dirac, and Feynman made
important contributions to this problem. By integrating their efforts, it is
then shown possible to construct a picture of the internal space-time symmetry
consistent with Einstein's Lorentz covariance.
