Unexpected cosmic clumping could disprove our best understanding of the universe

Hubble Space Telescope Image
The Hubble Space Telescope's deep field. (Image credit: NASA/ESA)

A survey of more than 25 million galaxies has found a strange contradiction in how astronomers measure the universe's clumpiness, and it could threaten the standard model of cosmology, which describes how the universe formed and evolved.

The discrepancy, found by measuring the warping of light by the powerful gravitational fields of distant galaxies, suggests that the cosmos is less packed-together than previously predicted.

If the measurement is accurate, it will join the Hubble tension as yet another significant challenge to our preconceptions of how the cosmos evolved — one that could give way to new physics or even an entirely different model of the universe. The researchers published their findings Dec. 11 in the journal Physical Review D.

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"We're still being fairly cautious here," Michael Strauss, chair of Princeton University's Department of Astrophysical Sciences and one of the leaders of the team that made the discovery, said in a statement. "We're not saying that we've just discovered that modern cosmology is all wrong. The statistics show that there's only a one in 20 chance that it's just due to chance, which is compelling but not completely definitive. But as we in the astronomy community come to the same conclusion over multiple experiments, as we keep on doing these measurements, perhaps we're finding that it's real."

According to the standard model of cosmology, after the Big Bang the young cosmos was a roiling plasma broth that began to rapidly expand due to an invisible force known as dark energy. As the universe grew, ordinary matter, which interacts with light, congealed around clumps of invisible dark matter to create the first galaxies, connected together by a vast cosmic web. Nowadays, cosmologists think that ordinary matter, dark matter and dark energy make up about 5%, 25% and 70% of the universe, respectively.

Yet there are growing problems with this picture. To test their models, astronomers often compare the past to the present universe. Their past measurements are drawn from the cosmic microwave background (CMB), the static fizz of the universe's first light that left its source (recombining atoms) 380,000 years after the Big Bang. 

Yet the Hubble constant — a value that tracks the expansion rate of the universe — predicted from the CMB disagreed with the calculations derived from celestial objects in the contemporary cosmos. This discrepancy has led to a crisis in cosmology known as the Hubble tension.

The new discrepancy about the lumpiness of the universe centers around a number called S8, which measures how much matter clusters, or clumps together, across the universe. After using the Planck satellite to study the cosmic microwave background (CMB), astronomers previously plugged the data into the standard model of cosmology and got a predicted value for S8 of 0.83


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This clashes with a new measurement of S8 using Japan's Subaru Telescope, which studied how much light is warped by the presence of matter in galaxies. Researchers took its results and produced a smaller value for S8 of 0.77. The new result was replicated by two other collaborations mapping the universe's matter with gravitational lensing — the Dark Energy Survey and the Kilo-Degree Survey — making an individual anomalous result unlikely.

"We're confirming a growing sense in the community that there is a real discrepancy between the measurement of clumping in the early universe (measured from the CMB) and that from the era of galaxies, 'only' 9 billion years ago," Arun Kannawadi, an associate research scholar at Princeton University who was involved in the analysis, said in the statement.

Though the problem points to yet another large hole in our understanding of the universe, cosmologists don't have great ways to fill it yet. It's possible that cosmologists are wrong about the amount of dark matter in the universe, or how it clumps together. Maybe dark energy changed over the course of the universe's life — an explanation that would resolve both the S8 and the Hubble tension with a tweak to the standard model of cosmology.

Or perhaps, most excitingly of all, it could mean that the standard model is broken and needs a total replacement. For scientists to know for certain, they will make more precise measurements from even more powerful telescopes. Two such contenders are the Vera C. Rubin Observatory in Chile and the Nancy Grace Roman Space Telescope, which are due to come online in 2025 and 2027, respectively.

Ben Turner
Staff Writer

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

  • Zaphod Beeblebrox
    Been reading "Biocentrism". Could Biocentrism play a new realm in our cosmic being?? Unless it is observed, does it really exist or is it just a probability? All interesting theories, but Biocentrism answers many holes our most prominent physicist/astro physicist could not explain...even Einstein. Even the "double slit" experiment is only verifiable by observation. We as the observer formulate the outcome. It is only the algorithms in our brain from our sensory perceptions that make a "picture" for us to comprehend and make sense/order of our existence. Is it really all an illusion??
  • Emerald Metaphor
    I agree whoelheartedly, but have gone further than that (I am a philosopher of mind, with actual degrees). The universe is a "Big Mind", it is biocentered and holographic, but the surface of the holgram is all the integrated surfaces of cells. Reality is first pre-entangled locally by non-conscious perception. Then as brains emerge this pre-entangled state is decohered into Naive Reality as Donald Hoffman describes, half as it is, half hacked. There is no Newtonian Box already out there! I am trying to get people to look at my work and I am here to help!

  • kba
    Accordingly to "Unified theory of Interactions" it isn't nesessary to add Dark matter to the Universe. The Dynamical gravity as a part of "Unified theory of Interactions" explains:
    1. An extravelocity for the stars on the galaxies' peripheria.
    2. High energy and velocity of cosmic rays. Also the "knee" in their energy spectrum as a border between galactic and extragalactic cosmic particles.
    3. Extravelocity for any objects we observe in the Universe.

    The "Unified theory of interactions" explains and describes many phenomenas, and able to build the Theory of Everything.

    E.g. it explains the quantumization of electron's orbit and other QM effects in the particles' interactions.
    It explains the essence of inertial mass as kind of gravitational one which interacts with masses of whole Universe.