Taking up superspace---the spacetime structure of supersymmetric field theory

Supersymmetry (SUSY) is a proposed symmetry between bosons and fermions. The structure of the space of SUSY generators is such that the distinction between internal and spacetime symmetries is blurred. As a result, there are two viable candidates for the correct spacetime setting for a flat supersymmetric field theory---Minkowski spacetime and superspace. an extension of four- dimensional Minkowski spacetime to include (at least) four new dimensions, coordinatised by mathematical objects known as supernumbers. These objects are, in one significant way, quite different from real or complex number---some of them have the property that their order of multiplication makes a difference; in mathematical terms, they are said to have nontrivial commutation properties. This paper argues for two theses: first, that one standard set of arguments, related to universality of symmetry behaviour, that motivate a particular choice of spacetime structure in familiar spacetime theories motivates the choice of superspace as the appropriate spacetime for SUSY field theories. And second, that the metaphysical utility of the concept of spacetime requires more than just the satisfaction of this universality condition; in supersymmetric theories, the spacetime concept is not as useful as in special relativity.