  A quantum picture of the causal structure of Minkowski space M is presented.
The mathematical model employed to this end is a non-classical version of the
classical topos {H} of real quaternion algebras used elsewhere to organize the
perceptions of spacetime events of a Boolean observer into M. Certain key
properties of this new quantum topos are highlighted by contrast against the
corresponding ones of its classical counterpart {H} modelling M and are seen to
accord with some key features of the algebraically quantized causal set
structure.
