  The k-calculus was advanced by Hermann Bondi as a means of explaining special
relativity using only simple algebra [1]. Bondi's argument was placed in the
context of classical electrodynamics. In this paper it is placed in context of
particle theoretic QED. The central derivations are reviewed, using proofs only
slightly more elegant than those in Bondi's books. As used by Bondi, k is
Doppler red shift. The relativistic measurement of position is placed in the
context of an information theoretic interpretation of quantum mechanics as a
theory of measurement results. The law of geodesic motion is seen as consequent
on the refraction of the wave function due curvature, as in geometric optics.
The k-calculus is extended to include gravitational red shift and to account
for gravity by observing that, after allowing a small inherent delay in the
reflection of a photon, the metric defined by the radar method obeys Einstein's
field equation. A very simple derivation of Schwarzschild is given using the
k-calculus and avoiding differential geometry and calculation of Christoffel
symbols. The Newtonian approximation is seen from a direct application of red
shift to the wave function.
