  Two-photon states produce enough symmetry needed for Dirac's construction of
the two-oscillator system which produces the Lie algebra for the O(3,2)
space-time symmetry. This O(3,2) group can be contracted to the inhomogeneous
Lorentz group which, according to Dirac, serves as the basic space-time
symmetry for quantum mechanics in the Lorentz-covariant world. Since the
harmonic oscillator serves as the language of Heisenberg's uncertainty
relations, it is right to say that the symmetry of the Lorentz-covariant world,
with Einstein's $E = mc^2$, is derivable from Heisenberg's uncertainty
relations.
