Avis Principle of Observational Lag

We present the Avis Principle of Observational Lag: a formal, unified statement of the proposition that no observer can receive information about an external object simultaneously with the moment of that object's emission. The finite propagation speed of all physical signals entails an irreducible temporal gap the observational lag between any event and its observation. We formalise this gap mathematically, introduce a state-gap term to measure its practical consequence, and establish a Planck-scale lower bound on its magnitude. We distinguish the Avis Principle from the existing concept of retarded time in electrodynamics, arguing that while the underlying physics is well known, its generalisation as a structural epistemic condition applicable uniformly across physical, biological, computational, and institutional systems has not been previously formalised. The corollary that the present state of any external object is permanently inaccessible to any observer follows directly. We survey implications across medicine, finance, strategy, control systems, and epistemology.