This work presents a formal geometric analysis of realism collapse in cinematic narratives. It introduces the concept of realism drift, a phenomenon arising when behaviour from a high‑dimensional expert manifold is projected into a low‑dimensional movie manifold, destroying essential constraints and producing unrealistic portrayals of surgeons, interrogators, doctors, and other specialists. The paper extends this framework using the Fast & Furious franchise as a longitudinal case study of manifold migration. Early films inhabit a realism manifold defined by physics, authenticity, and human vulnerability, while later films occupy a spectacle manifold characterised by superhero physics, meme‑aware escalation, and narrative invincibility. The work formalises all relevant manifolds, projection operators, migration operators, drift dynamics, entropy measures, orthogonality conditions, and optimisation constraints. It demonstrates that realism is not violated but displaced: experts appear unrealistic because they are projected into the wrong manifold, and franchises become unrealistic because they migrate into new ones. This document provides a complete mathematical, conceptual, and diagrammatic treatment of realism drift, honouring the original insight by Jonathan and fully formalised in the Carlo hybrid style. Keywords: realism drift, behavioural manifolds, expert manifold, movie manifold, realism manifold, spectacle manifold, projection operator, migration operator, dimensionality collapse, narrative compression, cinematic representation, expert misrepresentation, franchise evolution, Fast & Furious analysis, orthogonality geometry, realism entropy, drift dynamics, audience elasticity, spectacle pressure, manifold divergence, Carlo hybrid formalism, Jonathan-originated insight. Subjects: geometric modelling of narrative behaviour, applied manifold theory, cognitive representation in media, cinematic realism analysis, franchise drift studies, mathematical formalisation of storytelling constraints, expert behaviour projection, realism displacement, narrative physics, cultural evolution of film franchises, interdisciplinary media theory, conceptual modelling of cinematic exaggeration. Contact: For enquiries or research questions related to this work, email matthewcarlo.research@gmail.com