  The motivation for this article came from an attempt to give an alternative
definition for the meter, the SI unit for measuring length. As a starting point
towards this goal, in this piece of work we present the underlying theory
behind our approach which uses ideas from quantum field theory and
noncommutative geometry, in particular the notion of an odd K-cycle which is
based on the Dirac operator (and its inverse, the Dirac propagator). Using (the
perhaps more familiar) physics terminology, the key point in our strategy is
this: instead of measuring length directly in space-time we measure the
"algebraic (spectral) length" in the space of the corresponding quantum states
of some particle (fermion) acted upon by the Dirac propagator. This approach
shares the spirit of the unanimus vote of the 24th General Conference of
Standards and Measures (21st October 2011) in Serves, France for the
redefinition of the fundamental units using Planck's constant.
