Study suggests 2-billion light-year void
- Cosmologist Indranil Banik and colleagues argued a “local void” around the Milky Way could skew nearby expansion measurements, reviving a debated fix for Hubble tension. - The model requires Earth to sit near the center of an underdensity about 1 billion light-years in radius, with matter roughly 20% below average. - The claim extends 2025 baryon acoustic oscillation work and remains disputed against standard cosmology expectations. (arxiv.org)
The universe is expanding, but astronomers get two different answers for how fast. One camp measures the early universe; another measures nearby galaxies and supernovae. (arxiv.org) That mismatch is called the Hubble tension. In a February 2026 perspective paper, Indranil Banik, Harry Desmond, Vasileios Kalaitzidis and Sergij Mazurenko argued a large local underdensity could make nearby expansion look faster than the cosmic average. (arxiv.org) The basic idea is a cosmic valley: if the Milky Way sits in a region with less matter than average, gravity pulls galaxies outward toward denser surroundings. Those extra outward motions can inflate redshift-based local expansion estimates without changing the global expansion rate. (arxiv.org) (port.ac.uk) The scale in this proposal is enormous. Banik said in July 2025 that the Solar System would need to lie near the center of a void about 1 billion light-years in radius, or roughly 2 billion light-years across, with density about 20% below the cosmic average. (port.ac.uk) (phys.org) The new paper is not the first step in that argument. A 2025 preprint by Banik and Vasileios Kalaitzidis compared 42 baryon acoustic oscillation measurements — the leftover imprint of primordial sound waves — with void and no-void models. (arxiv.org) They reported a total chi-squared of 75.7 for the void-free model versus 47.3 to 51.2 for void models, cutting the stated tension from 3.3 sigma to about 1.1 to 1.4 sigma. The authors said the mismatch grows at lower redshift, where local structure should matter most. (arxiv.org) Banik’s July 2025 presentation at the Royal Astronomical Society’s National Astronomy Meeting framed those baryon acoustic oscillation results as support for the void picture. He also said the Hubble discrepancy appears mainly in the nearby universe, not at intermediate redshift. (port.ac.uk) (phys.org) That matters because a local-structure explanation would not require changing the physics of the early universe. It would shift attention toward mapping nearby galaxy density, bulk flows, and other late-time effects instead of adding new particles or fields. (arxiv.org) The catch is that the void itself is contested. The University of Portsmouth summary of Banik’s work said such a large, deep underdensity does not fit comfortably with the standard cosmology, which expects matter to be more uniform on those scales. (port.ac.uk) The February 2026 paper reads as a perspective and roadmap, not a final settlement. Its authors point to future tests including better local density maps, galaxy distance catalogs, kinematic Sunyaev-Zel'dovich measurements, fast radio bursts, and eventually redshift-drift observations. (arxiv.org) So the headline claim is narrower than “Earth is in a giant hole.” A group of cosmologists says a roughly 2-billion-light-year-wide local void could reconcile local and early-universe expansion measurements, and the next round of sky surveys will decide whether that picture holds. (arxiv.org)
