Nostalgia as Temporal Ground State Displacement: The Idealized Past as Unreachable Attractor, Bittersweet Return, and the Function of Longing

We apply the Displacement Framework to nostalgia, formalizing it as displacement toward a past S0 that is structurally unreachable — time is irreversible, so the past S0 is an absorbing state from the future's perspective. Seven formal propositions are derived: nostalgia as temporal displacement from past S0, temporal irreversibility as structural return blockade (the past as mathematical impossibility, not merely practical difficulty), idealization amplification (nostalgic memory systematically improves the remembered past), the Adaptive Nostalgia Theorem (representational return reduces D even without physical return — the memory itself provides partial S0 contact, explaining the bittersweet quality), pathological nostalgia as present-engagement wrong attractor (the contrast between idealized past and present becomes a stable wrong attractor preventing current-state engagement), homesickness as spatial nostalgia (potentially returnable if home still exists), and solastalgia (Albrecht) as ecological nostalgia structurally parallel to temporal nostalgia (landscape destroyed = past S0 unreachable).

Manufactured nostalgia in entertainment and advertising is analyzed as commercial exploitation of the nostalgic gradient. Frankl's permanence-of-the-past is formalized as the warrant for representational return — the past cannot be taken away, making memory a genuine (if partial) return path. 23 citations including Sedikides, Wildschut, Batcho, Boym, Albrecht, Frankl, Routledge, Davis, Zhou, and Hepper.