Framing the Possibility Space for Technosignature Searches

This paper develops a two-parameter matrix that can be used to describe four general strategies in the search for technosignatures. The first parameter is domain accessibility: can the technosignature be accessed within the spatial domain accessible to us today? The second parameter is recognizability: would the technosignature be recognizable to us if discovered today? This yields a matrix with four options that each comprise different search strategies. "Exploration" is the strategy for technosignatures that are accessible within our domain and recognizable, which includes radio and optical signals that have reached Earth and any artifacts that might be identifiable within the solar system. "Expansion" is the strategy for technosignatures that are recognizable but beyond our spatial domain, which includes diffuse technology elements that may exist in nearby systems but could not be remotely observed from Earth. "Evolution" is the strategy for technosignatures that are accessible within our domain but unrecognizable; this would require advances in sensory perception, technological or biological, before such technosignatures could be discovered. Finally, "Existence" is the strategy for technosignatures that are neither within our domain nor recognizable. The implications of these four options are discussed with relevance to the Fermi paradox and strategies for searching for technosignatures.