The fully covariant formulation of transformation optics is used to find theconfiguration of a cloaking device operating in an expanding universe modelledby a Friedmann-Lema\^itre-Robertson-Walker spacetime. This spacetime cloak isused as a platform for probing the covariant formulation of transformationoptics, thereby rigorously enhancing the conceptual understanding of thetheory. By studying the problem in both comoving and physical coordinates weexplicitly demonstrate the preservation of general covariance ofelectrodynamics under the transformation optics procedure. This platform alsoenables a detailed study of the various transformations that arise intransformation optics. We define a corporeal transformation as the"transformation" of transformation optics, and distinguish it from coordinateand frame transformations. We find that corporeal transformations considered inthe literature have generally been restricted to a subset of all possiblecorporeal transformations, providing a potential mechanism for increasedfunctionality of transformation optics.
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