Void edges are the transition zones where the nearly empty interior gives way to the surrounding filaments and walls, and many observed voids make that transition abruptly: galaxy counts and matter density climb steeply over a small radial range, producing quasi-compensated profiles with pronounced ridges at the boundary (Colberg et al. 2005; Hamaus et al. 2014).
The sharpness is the problem. In ΛCDM a void is the slow exhalation of an underdense Gaussian patch, matter drifting outward over billions of years, and gradual processes produce gradual profiles: simulations tend toward smoother, softer density transitions than the cliff-like edges some surveys report (Ceccarelli et al. 2013; Nadathur and Hotchkiss 2015). Reproducing the steep observed gradients within the model requires fine-tuned galaxy bias, elaborate feedback prescriptions, or selection arguments applied case by case, and each fix is calibrated to the data it explains rather than predicted in advance. The mismatch is mild compared to the headline anomalies, but it is persistent, and it compounds the rest of the void sector: the voids are too many, too empty, and too crisply drawn for a mechanism that only exhales.
The standing is a profile-shape argument heading toward precision resolution. Stacked void profiles from DESI and Euclid will measure edge gradients across thousands of voids with controlled selection, separating bias artifacts from a genuine structural feature of the web.