Einstein was well aware of Minkowski’s work though he
was initially unimpressed. Early on, he said it was “überflüssige Gelehrsamkeit,” superfluous learnedness, but he was soon moved to change his mind by the accomplishments of “Abraham, Planck, and Laue.” Einstein’s unpublished 1912 treatise embraced “Minkowski’s four-dimensional theory.” A vector in this space-time continuum, a 4-vector, is a special mathematical device which under a Lorentz transforma- tion changes its components but not its length. It is therefore invariant from one inertial frame to another. Because all inertial observers must experience the same laws of physics, valid physical quantities should be expressible in terms of 4-vectors.