Astronomers at the University of Portsmouth have a bold idea: what if Earth sits inside a massive cosmic void? That could explain why measurements of the universe’s expansion don’t line up.
Our Universe Is Expanding
Everyone agrees the universe is expanding. The Hubble constant measures that rate. But here’s the catch: distant, ancient observations predict a slower expansion than local data shows. This mismatch is the Hubble tension.
At a recent Royal Astronomical Society meeting, Portsmouth researchers suggested that if we’re in a one-billion-light-year-radius underdense region—about 20 percent less dense than average—gravity would drag matter outward. To us, that would look like faster local expansion.
If we are in a region with lower than average density, such as the green dot, matter would flow out due to the stronger gravity of the denser surrounding regions, as indicated by the red arrows. © Moritz Haslbauer and Zarija Lukic, University of Portsmouth
A One-Billion-Light-Year Void
Indranil Banik points out, “The Hubble tension is mostly local. On larger scales, the standard model holds.” Nearby galaxy counts back up the void theory, even though mainstream cosmology assumes a more uniform matter spread.
Baryon acoustic oscillations (BAOs) – the “Big Bang sound” – support the idea of a local vacuum. © Gabriela Secara, Perimeter Institute
A Confession from the Big Bang
The clue lies in baryon acoustic oscillations—the “sound waves” from the Big Bang. They froze into the early plasma and shaped today’s galaxy distribution. A local void would tweak the redshift we measure. Twenty years of BAO data make a void around us about 100 million times more likely than not. Next up: a “cosmic clock” test, comparing galaxy ages to their redshifts.
Nathalie Mayer
Journalist
Born in Lorraine on a freezing winter night, storytelling has always inspired me, first through my grandmother’s tales and later Stephen King’s imagination. A physicist turned science communicator, I’ve collaborated with institutions like CEA, Total, Engie, and Futura. Today, I focus on unraveling Earth’s complex environmental and energy challenges, blending science with storytelling to illuminate solutions.
