Can The Crisis in Cosmology Be SOLVED With Cosmic Voids?

Cosmic voids may be able to reshape two of cosmology’s biggest headaches at once: the “Hubble tension” (a roughly 10% mismatch between the universe’s expansion rate inferred from the early cosmos versus the rate measured nearby) and the need for dark energy as a separate ingredient in the standard model. The core idea is that the universe is not smooth on the scales assumed by Friedmann–Lemaître cosmology. Once the real clumpiness of matter—overdense superclusters and underdense voids—is treated more carefully, local motions can bias how the Hubble constant is measured, and in more ambitious proposals, the cumulative effect of voids could mimic the negative pressure usually attributed to dark energy.

The standard ΛCDM framework starts from Einstein’s general relativity and assumes matter is evenly distributed on large scales. That approximation works well for many predictions, but it hides how gravity actually behaves when matter is lumpy. On the local scale, the Milky Way sits in the Laniakea supercluster, a loose association of roughly 100,000 galaxies spanning about half a billion light-years. Because superclusters are not gravitationally bound, dark energy–driven expansion eventually disperses them. That environment should slow the outward recession of nearby galaxies relative to pure expansion, meaning a Hubble-constant measurement based on Laniakea galaxies would come out too low.

A study by Leonardo Giani and collaborators quantifies how much that local environment could bias measurements: the local Hubble constant could be more than 1% too low because of Laniakea’s gravitational influence. That matters because it makes it harder to dismiss the Hubble tension as purely a local artifact—though it doesn’t automatically solve the problem.

Zooming outward introduces the opposite effect. The Milky Way lies near the center of a large underdense region sometimes called the Local Hole (the Keenan-Barger-Lenox Void), roughly 2 billion light-years across. Inside a void, gravity pulls outward toward the void’s denser boundary, boosting galaxy velocities above what uniform expansion predicts. If that boost is not properly accounted for, the inferred Hubble constant can look too large—potentially easing the tension by bringing the modern measurement closer to the value expected from the cosmic microwave background under ΛCDM.

One claim comes from Shanks, Hogarth, and Metcalf (2019), who combine distance calibrations using Cepheid variables from the Gaia satellite with measurements of outflow velocities within the Local Hole. They report a “true” modern Hubble constant around 69 rather than 73.5, aligning more closely with early-universe expectations. But the void picture is contested. Building a reliable three-dimensional map of matter and velocities at gigaparsec scales is difficult, and different distance and velocity datasets can disagree. Adam Reiss and collaborators, using supernova-based atlases, argue the Local Hole is barely present. Others question whether ΛCDM can even generate such a huge void given the tiny initial fluctuations seen in the cosmic microwave background.

At the farthest extreme, an Iranian team proposes that dark energy itself could be the net effect of cosmic voids. In their model, voids behave like “bubbles” whose expanding surfaces—formed by galaxy sheets and filaments—create an effective negative pressure analogous to the surface tension effect in fluid bubbles. If void-driven negative pressure is large enough, it could reproduce the acceleration usually attributed to vacuum energy. The hypothesis is speculative, and the transcript emphasizes that dark energy could still be a simple vacuum property, leaving the Hubble tension to local measurement bias—possibly tied to voids.

Either way, the takeaway is clear: understanding the universe’s least populated regions—cosmic voids—may be essential, not peripheral, to resolving both the expansion-rate mismatch and the physical origin of cosmic acceleration.