Galaxy counts and distance-redshift surveys keep suggesting that we live somewhere unusual: the region around the Local Group out to a few hundred megaparsecs appears significantly underdense, the KBC void or Local Hole, with estimated deficits of 20 to 50 percent against the cosmic mean depending on tracer and depth (Keenan et al. 2013; Haslbauer et al. 2020). An underdensity that deep over a volume that large is a structure the standard model struggles to build.
The challenge runs on two tracks. Statistically, voids of the KBC's scale and depth are rare in ΛCDM simulations grown from Gaussian initial conditions, rare enough that finding ourselves inside one strains the assumption that we occupy a typical location. Dynamically, the void cuts both ways: it would raise the locally inferred H0 and thereby help the Hubble tension, but detailed analyses find that a ΛCDM-consistent void cannot be deep enough to carry the full tension without violating BAO, supernova, and large-scale structure constraints (Huterer and Wu 2023; Stiskalek et al. 2025). The model is left defending an improbable structure that is also insufficient for the job it might have done.
The standing is genuinely contested, with void-depth estimates varying by tracer and the simulation rarity arguments sensitive to definition. DESI and Euclid will map the local density field with enough depth and sky coverage to fix the void's profile decisively, and with it both the statistical and the dynamical halves of the problem.