Inside the Output Envelope: Detection-assumption violations, and why atmospheric searches cannot distinguish chemistry, life, and mind

Abstract The search for life and for technology beyond Earth returns its results against a set of assumptions about what life and technology look like from a distance, and those assumptions are usually invisible because they match our own case. This paper makes the assumptions explicit, shows each one defines a class of world that becomes undetectable when the assumption fails, and develops the consequence in full for two such classes. The unifying construct is the output envelope, the set of atmospheric and observable outputs that natural and self-regulating systems can produce. Detectability is a property of whether an output falls inside or outside that envelope, and it is orthogonal to the agency behind the output. From this follows a two-sided result. A technological civilization whose industry stays inside the envelope presents as a biosignature, so technology can hide as life, and a biosignature cannot reveal whether agency lies behind it at any level from blind self-regulation to industrial cultivation, so life is silent on mind. The inside-envelope region is therefore opaque to agency in both directions, and the two classes that demonstrate this turn out to be one continuum viewed from its two ends. We present the general method that produced these results, the grading discipline that lets speculative cases contribute without contaminating solid ones, the two worked classes, four further classes graded but not yet developed, and the limits of the whole program. This provides a framework and a hard limit on inference, contributing to the argument that the evidential weight of a non-detection depends on the object class it is tied to, and that a wide range of object classes, including some that track the most common stars in the galaxy, have not been defined and cannot be detected by current means.