A novel physical framework seeks to account for peculiar measurements of galaxy recession speeds by positing that empty space functions like a fluid endowed with drag.
Under this conception, the force driving the Universe’s expansion would not be static over time but could instead intensify, diminish, or momentarily exceed acceptable limits, thus altering our current comprehension of dark energy.
New distance measurements, derived from the Dark Energy Spectroscopic Instrument (DESI), have revealed a slight discrepancy in results that otherwise align closely with cosmic history.
To address this issue, Muhammad Ghulam Khwaja Khan of the Indian Institute of Technology in Jodhpur (IIT Jodhpur) has formulated a model that incorporates air resistance analogs.
In a recent preprint paper uploaded to arXiv, Khan of IIT treats expanding space as something that inherently resists stretching and subsequently relaxes.
Should this tension persist, the next hurdle will be to articulate what physical resistance empty space could actually offer.
Resistance within vacuum space would oppose expansion, rendering the Universe somewhat “more viscous” than an immaculate void.
Physicists term this bulk viscosity—a resistance to volume change during expansion—which manifests as an extra pressure component.
Bulk viscosity only exerts a counterforce when space’s dimensions are changing, meaning faster expansion generates greater pressure than slower expansion.
Viscosity therefore appears an appealing candidate for underpinning the analysis of cosmic data, though labeling the cosmos a “sticky fluid” still requires proper justification.
The majority of cosmological models attribute the Universe’s acceleration to the introduction of a smooth component that behaves uniformly everywhere.
Cosmologists refer to this as dark energy—an unknown pressure source that speeds up cosmic expansion even as matter pulls inward via gravity.
For decades, numerous analyses assumed this driving impulse remains constant throughout time, meaning it could be described by a single numerical value.
This constant magnitude is the cosmological constant, fixed energy resident in the vacuum, and the tension exerts pressure upon it.
To generate this “resisting” pressure, Khan endowed space with an internal mechanism allowing it to oscillate during expansion. In materials science, phonons, collective vibrations propagating through a solid, transport energy without moving matter.
Khan extended this concept to the vacuum, describing longitudinal waves that propagate through space and generate resistance.
Since these waves react to the expansion, the model links small-scale activity within space to the large-scale speed of galaxies.
In Khan’s scenario, the atmospheric drag does not remain fully engaged eternally; his equations dictate that it is a transient effect.
Instead, the pressure lags behind the expansion due to an embedded delay, causing the resistance to peak during specific epochs.
At the beginning and in the far future, the model reverts to nearly constant behavior, exhibiting only a minor surge during the intermediate phase.
Such an effect, confined to a temporal window, can mimic changing acceleration but also makes the idea easier to falsify.
The most compelling data points derived from DESI come from the repeating pattern of galaxy separation, which serves as a standard cosmic yardstick for mapping distances.
Cosmologists refer to this signature as baryon acoustic oscillations—the leftover imprint of sound waves from the early Universe—and DESI has tracked its evolution over time.
At IIT, the team fine-tuned its hydrodynamic equations until the scale factor matched what DESI observed, spanning several cosmic epochs.
Because the model is inference-based on observations rather than derived from particle physics principles, its validity hinges on future scrutiny.
Other measurements of sky parameters track expansion through different means, and a viscous Universe ought to correlate with those as well.
Both supernovae distance markers and the growth of galaxy clusters respond to the rate of expansion, so the damping effect must influence both phenomena.
The bending of light via gravitational lensing, which distorts images due to mass, also depends on how structure evolves under the influence of drag.
If even one of these checks fails, the viscosity will remain merely a clever curve-fitting approximation rather than an actual property of space.
Caution is warranted here, as Khan released his work prior to peer review, and the concept may not pass basic scrutiny.
In conventional fluids, viscosity arises from momentum exchange between particles; thus, a credible source is necessary to constitute a vacuum medium.
A recent paper demonstrated how bulk viscosity models can run into internal paradoxes when tuned too rigidly.
Until a physical explanation for this phenomenon is established and corroborated by other datasets, the model stands as only an intriguing temporary fix.
Yes. You can focus on the test itself rather than the instruments. Here is a more concise version that avoids mentioning multiple telescopes:
Further observation will determine whether the tension persists, with the next decade offering the clearest verdict.
Ongoing galaxy surveys will measure the rate of spatial expansion across different stages of cosmic history. Future maps charting billions of galaxies will reveal whether expansion truly changes as the viscosity model predicts.
If the results from these independent probes align, the case for a cosmic drag theory strengthens, but if they diverge, the idea is likely to be discarded.
Khan’s model transforms an abstract inconsistency into a concrete proposition: empty space exerts resistance during expansion.
Should upcoming galaxy surveys confirm this very pattern of dark energy influence, cosmologists might replace the static picture of dark energy with one that evolves over time—though only following rigorous validation.
About the Author
