The galaxies within a few megaparsecs of the Local Group recede with astonishing orderliness: the peculiar-velocity dispersion around the local Hubble flow is only 30 to 70 km/s depending on sample and distance range, with HST-based measurements by Karachentsev and collaborators near 30 km/s. This coldness is a long-standing puzzle, posed by Sandage as the surprise that a "noisy" gravitating neighborhood produces so quiet a flow. Cold dark matter simulations of hierarchical structure formation systematically fail to reproduce it: regions resembling our neighborhood, with its giants, groups, and recent dynamical history, show predicted dispersions two to several times larger than observed.
The proposed ΛCDM rescue, that dark energy smooths the local flow by suppressing peculiar velocity growth (Chernin, Baryshev), has not survived scrutiny: constrained simulations of the actual local volume (Hoffman et al.) find dark energy makes essentially no difference to local dynamics on these scales, identifying the local matter distribution as the relevant factor without explaining why our particular environment should be so dynamically gentle. The puzzle is thus orphaned: the model's own simulations cannot produce the observed coldness from its initial conditions, the dark energy explanation is broken, and appeals to our neighborhood being a statistical outlier must contend with the flow being cold in every direction sampled.
The standing is quiet but persistent: the measurement is robust and improving with Gaia and HST/JWST distances to nearby galaxies, while the theory side has largely set the problem aside. A local volume whose flow noise sits far below hierarchical expectations remains an unexplained property of our immediate cosmic environment, the part of the universe we can measure best.