A new physics model attempts to explain puzzling measurements of how fast galaxies are moving away from us, proposing that empty space behaves like a fluid with built-in drag.
In this view, the force driving the universe’s expansion would not stay constant over time, but could strengthen, weaken, or briefly overshoot, changing how we understand dark energy.
Clues from DESI
Fresh distance measurements from the Dark Energy Spectroscopic Instrument (DESI) revealed a small mismatch in results that otherwise track cosmic history well.
Targeting that tension, Muhammad Ghulam Khuwajah Khan at Indian Institute of Technology Jodhpur, (IIT Jodhpur) built a model adding drag.
In a new preprint, Khan at IIT treated expanding space as something that resists stretching, then eases off later.
If the tension holds up, the next step is to explain what kind of physical resistance empty space could have.
What viscosity changes
Resistance in empty space would oppose expansion, making the universe a bit “stickier” than a perfect vacuum.
Physicists call this bulk viscosity, resistance to volume change during expansion, and it shows up as extra pressure.
Bulk viscosity pushes back only when space changes size, so faster expansion produced more pressure than slower expansion.
That makes viscosity tempting as a patch for cosmic data, but calling space a “sticky fluid” still demands a real cause.
Dark energy assumptions
Most cosmology models explain the universe’s speeding-up by adding a smooth ingredient that behaves the same everywhere.
Cosmologists call it dark energy, an unknown source of pressure that speeds cosmic expansion, even as matter pulls inward.
For decades, many analyses assumed this push stayed constant over time, so one number could describe it.
That constant option is the cosmological constant, a fixed energy in empty space, and the tension pressures it.
Space can vibrate
To create that turning-on pressure, Khan gave space an internal way to wobble as it expanded. In materials science, phonons, collective vibrations moving through a solid, carry energy without carrying matter.
Khan extended that idea to the vacuum, describing longitudinal ripples that travel through space and create resistance.
As those ripples respond to expansion, the model links small-scale motion inside space to the large-scale speed of galaxies.
When drag turns
Drag in Khan’s universe did not run at full strength forever, and his equations made it temporary.
Instead, pressure lagged behind expansion by a built-in delay, so the resistance peaked during certain eras.
Early on and far in the future, the model settled back toward a near-constant behavior, leaving only a mid-era increase.
Such a time-windowed effect can mimic a changing acceleration, but it also makes the idea easy to falsify.
Matching the pattern
DESI’s strongest clues come from a repeating separation pattern in galaxies, which provides a standard distance scale for cosmic maps.
Cosmologists call that signal baryon acoustic oscillations, a leftover pattern from early-universe sound waves, and DESI measured it across time.
At IIT, the team tuned his fluid equations until that scale landed where DESI saw it, across several eras.
Because the model chased observations rather than building from particle physics, it stands or falls on future surveys.
Predictions in data
Other sky measurements track expansion in different ways, and a viscous universe would need to agree with them too.
Supernova distance markers and the growth of galaxy clusters both respond to the expansion rate, so drag changes both.
Light bending by gravitational lensing, warping of images by mass, also depends on how structure grows under drag.
Failing any one of those cross-checks would leave viscosity as a clever curve-fit, not a property of space.
Limits of the idea
Caution matters here because Khan posted the work before peer review, and the idea could fail basic checks.
In ordinary fluids, viscosity comes from particles exchanging momentum, so an empty vacuum needs a believable source.
A recent paper laid out how bulk viscosity models can run into internal contradictions when tuned too hard.
Until a physical mechanism explains the drag and other datasets agree, the model remains an interesting placeholder.
Yes. You can keep the focus on the test rather than the instruments. Here is a cleaner version that avoids naming multiple telescopes:
New model for universe expansion
More observing time will decide whether the tension survives, and the next decade offers the clearest verdict.
Ongoing galaxy surveys will keep measuring how fast space expands across different eras of cosmic history. Future maps of billions of galaxies will show whether the expansion truly changes in the way a viscous model predicts.
If those independent measurements line up, the case for cosmic drag strengthens, but if they conflict, the idea likely fades.
Khan’s model turns an abstract mismatch into a clear claim that empty space pushes back when it expands.
If upcoming galaxy surveys confirm the same drag pattern, cosmologists may replace a fixed dark energy picture with a time-changing one, though only after careful checks.
The study is published in arXiv.
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