Harmonic Oscillators as Bridges between Theories

Let us see how these great physicists used harmonic oscillators to establish beachheads to new physics.

Can harmonic oscillators serve as a bridge between quantum mechanics and special relativity?

The photos of Einstein, Heisenberg, Schroedinger, Dirac, Yukawa, and Feynman are from the Niels Bohr Photo Library of the American Physics Institute. License fees paid.