Physics

Spacetime defects uncouple gravity from mass in dark matter alternative

Can gravity exist without mass? A new study proposes a way it might, with drastic effects on dark matter models
NASA/JPL-Caltech
Can gravity exist without mass? A new study proposes a way it might, with drastic effects on dark matter models
NASA/JPL-Caltech

Something seems to be missing from the universe, and the favored model of physics calls it “dark matter” – but despite a century of searching, it remains a no-show. A new paper proposes an alternative hypothesis, showing how gravity could exist without mass and produce many of the same effects we ascribe to dark matter.

Einstein’s theory of general relativity is still our best model for describing gravity. As you might remember from high school physics class, gravity is the force that arises from masses resting on the fabric of spacetime. The more mass an object has, the deeper the “dip” in spacetime and the stronger the gravitational pull.

But starting in the 1930s, some strange astronomical observations began to raise questions. Galaxy clusters seemed to be moving much too fast to stay stable based on visible matter, suggesting that far more matter was present than we could see. That led to the hypothesis that huge amounts of invisible stuff – which was dubbed dark matter – pervaded the universe. The idea has held surprisingly strong in observations in the decades since, backed up by the motions of stars within galaxies and the bending and magnifying of light through gravitational lenses.

A good hypothesis is always testable, and so physicists concocted plenty of experiments designed to detect a range of plausible dark matter particles. But so far, all have come up empty, leading some scientists to propose alternatives like modified gravity or even a “dark fluid” permeating the cosmos.

A new paper, by Dr. Richard Lieu at the University of Alabama in Huntsville (UAH), suggests a new idea entirely. Topological defects in the cosmos, which could have been formed during a phase transition in the early universe, could exert a gravitational influence on nearby objects and passing light, but have zero mass themselves.

“Topological effects are very compact regions of space with a very high density of matter, usually in the form of linear structures known as cosmic strings, although 2D structures such as spherical shells are also possible,” said Lieu. “The shells in my paper consist of a thin inner layer of positive mass and a thin outer layer of negative mass; the total mass of both layers – which is all one could measure, mass-wise – is exactly zero, but when a star lies on this shell it experiences a large gravitational force pulling it towards the center of the shell.”

This could explain how stars can move faster than they “should” be able to according to their visible mass, and how galaxies and clusters hold themselves together. And if these shells form groups of concentric rings, they could also explain observations of gravitational lenses, which magnify distant light sources.

“Gravitational bending of light by a set of concentric singular shells comprising a galaxy or cluster is due to a ray of light being deflected slightly inwards – that is, towards the center of the large-scale structure, or the set of shells – as it passes through one shell,” said Lieu. “The sum total effect of passage through many shells is a finite and measurable total deflection which mimics the presence of a large amount of dark matter in much the same way as the velocity of stellar orbits.”

It might sound a bit too convenient to invent a new phenomenon out of nowhere, but it’s not without some merit. First, negative mass sounds like a sci-fi concept, but it has been modeled before, and some of its expected properties – such as an object flowing backwards when you push on it – have even been demonstrated in fluids and particles. Second, gigantic ring structures seen in space, which can’t currently be explained through dark matter, could be evidence of these topological defects.

It’s an intriguing idea, albeit one that still has a few holes to plug up. For one, the paper doesn’t attempt to explain how the defects form in the first place. There’s also the problem of how these shell structures could be confirmed or ruled out through observations. And finally, Lieu admits that it might not be enough to remove the need for dark matter entirely, but could just reduce its role.

Still, it’s the first model that suggests gravity could exist without mass, and future work could investigate how the structures might form and how they could guide galaxies and clusters to form.

The research was published in the journal Monthly Notices of the Royal Astronomical Society.

Source: UAH

  • Facebook
  • Twitter
  • Flipboard
  • LinkedIn
7 comments
Nobody
Simple answer. The universe is much older than 13.7 billion years. Dark matter is just older cold ordinary matter. The James Webb telescope is proving it.
Uncle Anonymous
@ Nobody... If it is so simple, why don't you report your findings to the Royal Swedish Academy of Sciences and collect your Nobel Prize? 🤔
Nobody
@Uncle Anonymous, I have put my theories on the internet may times over the past 20 years. But I am Nobody and not part of the intellectual insider club. However, my theories are looking much better than theirs since the James Webb data started coming out. Much better.
Rob Tillaart
Fascinating stuff,

Could dark matter be the gravity we feel from mass from one or more parallel universes?
Similar like the magnet under the paper attracting a magnet above but not visible and then in 4 (or more) dimensions?
Nobody
In case you missed my earlier theories. The Big Bang always needed extra explanations like the inflation theory, dark matter, and dark energy to prop it up. I have proposed for years that the universe was more likely 50-100 billion years old rather than 13.7 billion. The longer time line allows for slower expansion and more generations of stars to synthesize the heavy elements. It also allows older generations of normal stars to cool and become what appears to be dark matter and not something mysterious. After 6 or 7 generations of stars with 30% not reforming from each generation of novae or super novae, less than 10% of all matter would still be hot and visible while the rest would be cold dark normal matter but still exert gravitational influence. If the Big Bang was only 13.7 billion years old, all of these distant galaxies would have to be popping all over with super novae and extremely brilliant but with not enough time to synthesize all the heavy elements from repeated generations of stars.

Ranscapture
@Nobody, is correct and what I also keep saying. These scientists are just being complicated for funding. And I hate to burst your bubbles, but in space, there is no such thing as moving through space, only relative to another object. The galaxies that they observed accelerating away from us would be observed by our position in the Milky Way spinning around its SMB, once we start the part of the rotation back towards it, they’ll see the galaxy slowing down and think it must be dark matter again.
Ranscapture
I forgot to say: the only thing that happens in space is acceleration or deceleration in a direction, which you will feel as G-force, once that is done, you are no longer moving through space, only in relation to other objects in space.