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Scientists have proposed a wild new theory at the Royal Astronomical Society's National Astronomy Meeting (NAM) in Durham - Earth, along with the entire Milky Way galaxy, may be situated within a billion light-year-wide cosmic void.
This hypothesis, if confirmed, could resolve the perplexing 'Hubble tension' and fundamentally reshape our understanding of the universe’s expansion and its estimated age of 13.8 billion years.
The Hubble tension refers to a persistent discrepancy between the predicted and observed rates of the universe’s expansion. Introduced by Edwin Hubble in 1929, the Hubble constant measures how quickly celestial objects, such as galaxies, are moving away from us as the universe expands. Current cosmological models, based on a uniform distribution of matter, predict a slower expansion rate than what astronomers observe, particularly in our local universe. This mismatch has puzzled scientists for years, prompting the search for new explanations.
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Dr. Indranil Banik from the University of Portsmouth presented a potential solution at NAM 2025, suggesting that "our galaxy is close to the centre of a large, local void." As per this explanation, the Milky Way resides in a region of space with significantly fewer galaxies, stars, and other cosmic matter compared to denser surrounding areas. As matter is gravitationally pulled toward these denser regions, the void empties, causing objects within it to move away from each other at a faster rate. This creates the appearance of an accelerated local expansion, potentially explaining the Hubble tension.
However, this idea challenges the standard cosmological model, which assumes a relatively uniform distribution of matter across large scales. To bolster their case, Dr. Banik and his team turned to baryon acoustic oscillations (BAOs), described as the "sound of the Big Bang." These primordial sound waves, which traveled briefly before becoming fixed in place as the universe cooled and formed neutral atoms, serve as a cosmic yardstick.
While the local void theory offers a compelling explanation for the Hubble tension, it remains controversial and requires further testing. Future research will compare this model with alternative methods for estimating the universe's expansion history, such as cosmic chronometers. These involve studying galaxies that no longer form stars to determine their age and expansion metrics. By analysing the spectra (range of wavelengths of light) of these galaxies, astronomers can identify the types of stars they contain and combine this data with redshift measurements to refine our understanding of cosmic expansion.
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(Image: ESA)
