- Earth could be located inside a billion-light-year-wide void, astronomers say.
- This could explain the Hubble tension, or disagreements in measurements of how fast the universe is expanding.
- The evidence comes in the form of sound waves from the Big Bang known as baryon acoustic oscillations.
The Royal Astronomical Society published this story on July 8, 2025. Edits by EarthSky.
Is Earth in a huge void? Sound waves from the Big Bang suggest so
Earth and our entire Milky Way galaxy may sit inside a mysterious giant hole which makes the cosmos expand faster here than in neighboring regions of the universe, astronomers say.
Their theory is a potential solution to the Hubble tension and could help confirm the true age of our universe, which is estimated to be around 13.8 billion years old.
The latest research – which will be shared at the Royal Astronomical Society’s National Astronomy Meeting (NAM) in Durham, U.K., on July 9, 2025 – shows that sound waves from the early universe, which the scientists call “essentially the sound of the Big Bang,” support this idea.
Could a void explain the Hubble tension?
The Hubble constant was first proposed by Edwin Hubble in 1929 to express the rate of the universe’s expansion. It can be measured by observing the distance of celestial objects and how fast they are moving away from us.
The stumbling block, however, is that extrapolating measurements of the distant, early universe to today using the standard cosmological model predicts a slower rate of expansion than measurements of the nearby, more recent universe. This is the Hubble tension.
Study lead Indranil Banik of the University of Portsmouth explained:
A potential solution to this inconsistency is that our galaxy is close to the center of a large, local void. It would cause matter to be pulled by gravity toward the higher density exterior of the void, leading to the void becoming emptier with time.
As the void is emptying out, the velocity of objects away from us would be larger than if the void were not there. This therefore gives the appearance of a faster local expansion rate.
He added:
The Hubble tension is largely a local phenomenon, with little evidence that the expansion rate disagrees with expectations in the standard cosmology further back in time. So a local solution like a local void is a promising way to go about solving the problem.
What’s the evidence?
For the idea to stand up, Earth and our solar system would need to be near the center of a void about a billion light-years in radius and with a density about 20% below the average for the universe as a whole.
Directly counting galaxies does support the theory, because the number density in our local universe is lower than in neighboring regions.
However, the existence of such a large and deep void is controversial because it doesn’t mesh particularly well with the standard model of cosmology, which suggests matter today should be more uniformly spread out on such large scales.
Despite this, new data that Banik will present at the Royal Astronomical Society’s National Astronomy Meeting 2025 shows that baryon acoustic oscillations (BAOs) – the “sound of the Big Bang” – support the idea of a local void.
He explained:
These sound waves traveled for only a short while before becoming frozen in place once the universe cooled enough for neutral atoms to form. They act as a standard ruler, whose angular size we can use to chart the cosmic expansion history.
According to the study, a billion-light-year void around Earth would distort the relationship between the size of these sound waves and measurements of redshift, which is what astronomers use to measure how quickly things are moving away in space.
Banik said:
By considering all available baryon acoustic oscillation (BAO) measurements over the last 20 years, we showed that a void model is about 100 million times more likely than a void-free model with parameters designed to fit the cosmic microwave background (CMB) observations taken by the Planck satellite.
Next steps
The next step for researchers is to compare their local void model with other methods to estimate the history of the universe’s expansion, such as cosmic chronometers.
This involves looking at galaxies that are no longer forming stars. By observing their spectra, or light, it is possible to find what kinds of stars they have and in what proportion. Since more massive stars have shorter lives, they are absent in older galaxies, providing a way to establish a galaxy’s age.
Astronomers can then combine this age with the galaxy’s redshift – how much the wavelength of its light has been stretched – which tells us how much the universe has expanded while light from the galaxy was traveling toward us. This sheds light on the universe’s expansion history.
Bottom line: New research says sound waves from the Big Bang support the idea that Earth is in a huge void, which could explain the Hubble tension.
Source: Theoretical and observational approaches to the Hubble tension
Via Royal Astronomical Society
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