Recent observations have revealed that our understanding of the cosmos is flawed, but it may be because the universe is “stickier” than we assumed, new research proposes.
In a paper that was published on the arXiv preprint server but has not been peer-reviewed, Muhammad Ghulam Khuwajah Khan, a researcher at the Indian Institute of Technology, suggests that space may possess a property called bulk viscosity.
Viscosity is a measure of how much a fluid resists flowing or changing shape — like the difference between pouring water versus honey. In this case, we are talking about the bulk viscosity of the vacuum itself, a ghostly resistance that occurs when space expands.
A constant problem
Traditionally, scientists have used a simple model to describe the universe. In this model, known as Lambda-CDM, dark energy — the mysterious force responsible for the accelerating expansion of the universe — is a steady, unchanging background known as the cosmological constant.
However, data from the Dark Energy Spectroscopic Instrument (DESI), which is mounted on the Mayall Telescope at Kitt Peak National Observatory in Arizona, released last year hinted that something may be fundamentally wrong with our understanding of dark energy. The new observations showed a slight mismatch between our standard theories and the actual, observed rate at which galaxies are zipping away from us.
To explain this discrepancy, Khan has proposed a model involving spatial “phonons.” In solid-state physics, phonons are essentially the collective vibrations of atoms in a crystal. But Khan applied this idea to the fabric of space itself. He suggested that these longitudinal vibrations, which would act as sound waves of the vacuum, could be responsible for a viscous effect that slowed the expansion of the cosmos just enough to match what we see in the sky.
By treating the universe as a viscous fluid, this model introduces a drag on cosmic expansion. As space stretches, these spatial phonons slosh around, creating a pressure that opposes the outward push. In fact, the study shows that this simple, data-based model fits the DESI data with great precision, potentially solving some of the headaches caused by the standard cosmological constant.
But we should tread lightly — this is merely a guess. Viscous dark energy would be a foundational shift in how we view the vacuum of space, and the hard data from DESI are still being analyzed by the scientific community. We aren’t yet sure if this viscosity is a fundamental property of nature or just a sluggish artifact of our current measurements.
So, where do we go from here? The next decade of data from missions like the Euclid space telescope and continued monitoring by DESI will be the ultimate test. We need more observations to see if these ghostly vibrations are truly ruling the cosmos, or if space is as smooth as we once believed.
