The Third Law of Information: _"Information Has No Intrinsic Decay Term"_

We propose and formalize the **Third Law of Information**: “Information has no intrinsic decay term.” This law asserts that information admits no fundamental physical process by which it gradually degrades or ceases to exist in a closed system under unitary time development. This is distinct from practical inaccessibility (hiding via dispersal or entropy increase) and from dynamical redistribution (transformation). The law constrains any putative decay mechanism analogous to radioactive decay or damping terms, requiring that information persistence be indefinite in the absence of non-unitary processes. Building on the First Law (information cannot originate from no information) and the Second Law (information cannot be destroyed; only transformed or hidden), the Third Law completes a foundational triad. We present logical justification, theoretical foundations, and supporting experimental evidence from tests of unitarity, no-hiding, and long-term quantum coherence. The Third Law extends the conservation of information into indefinite temporal persistence under fundamental dynamics.