Universal center-of-mass scaling shapes segment fluctuations and chromatin dynamics

We show that cancellation of internal forces together with spatially uncorrelated noise generically enforces a universal 1 / s scaling of the center-of-mass (COM) diffusivity for polymer segments of contour length s , independent of model details. Within an active generalized Rouse-Langevin (A-GRLE) framework for fractal polymers in a viscoelastic bath with weak activity, we derive closed-form links between segment COM motion and the short-time behavior of two-point fluctuations. The same COM law predicts transient s − 3 tangent-tangent correlations along the contour following a temperature quench. Reanalyzing recent two-locus chromatin tracking, we extract a dynamic COM exponent ξ = 0.77 ± 0.16 , suggesting topological constraints. These results identify model-independent signatures of collective polymer dynamics and clarify that the observed Rouse-like scaling of chromatin loci reflects transient, unentangled dynamics with an inevitable crossover to an entangled regime at longer times.