A recent study that presents new challenges to the existence of dark matter suggests gravity may be able to exist even in the absence of mass.
Although all life on Earth experiences its effects daily, gravity remains one of the great mysteries of modern physics. Now, a new study published by Dr. Richard Lieu with The University of Alabama in Huntsville (UAH) proposes that the gravitational effects observed in galaxies and clusters may be the result of what he likens to topological defects in the universe, a theory that does not require the inclusion of dark matter to explain phenomena observed in our universe.
A hypothetical nonluminous material believed by many to account for as much as 85% of the mass in the known universe, dark matter was initially conceived to help account for gravitational effects that scientists presently cannot explain with Einstein’s theory of general relativity. First proposed in 1932 by Dutch astronomer Jan Oort, astrophysicists have continued searching for evidence of this mysterious invisible material, which remains unconfirmed.
However, not everyone is convinced that dark matter offers the best solution to the questions astrophysicists have about the cosmos. In his recent study, Lieu suggests an entirely new approach that could fundamentally upend our current understanding of the universe’s mass and gravitational forces.
“My own inspiration came from my pursuit for another solution to the gravitational field equations of general relativity—the simplified version of which, applicable to the conditions of galaxies and clusters of galaxies, is known as the Poisson equation,” Lieu recently said of his unique approach.
A distinguished professor of physics and astronomy at UAH, Lieu says that his interpretation of the problem “gives a finite gravitation force in the absence of any detectable mass,” an approach that he says arose from his frustration with prevailing ideas about dark matter that still lack any direct evidence after more than a century since the idea was initially proposed.
According to Lieu, concentric structures comprised of shell-like topological defects could account for the excess gravity current models require to bind galaxies or clusters. These structures likely have their genesis in a cosmological phase transition—an event where the state of matter changes across the entire universe—which occurred very early in the universe.
Lieu says such a phase transition could potentially generate gravitational effects without mass.
“Topological defects are compact regions of space with a very high density of matter, usually in the form of cosmic strings or spherical shells,” Lieu said in a statement. These spherical shells would likely consist of an inner layer of positive mass surrounded by an exterior layer composed of negative mass. The result would be a structure possessing a net mass of zero. Despite having essentially no mass, objects near these shells would nonetheless experience significant gravitational forces attracting them toward their center.
According to Einstein’s theories, gravity warps space-time, causing interactions between objects regardless of their mass. Even massless photons are influenced by gravity, for example, when light is warped as it passes near extremely dense celestial objects.
For Lieu, observations of the deflection of light and the velocities of stellar orbits in galaxies may be the result of these hypothetical massless shells, which he believes could offer a better explanation than the theoretical existence of dark matter in these regions.
Although Lieu does not currently offer an explanation for how these massless shells could be formed, he does say that his alternative theory could lead to new discoveries that could resolve such longstanding questions or may even help us confirm the existence of dark matter.
“The availability of a second solution, even if highly suggestive, is not sufficient to discredit the dark matter hypothesis,” Lieu says, adding that his study may only be “an interesting mathematical exercise at best.”
If proven through additional research, however, Lieu’s theory could indeed offer proof that gravity can exist without a need for mass. This discovery could potentially represent a significant advancement in our understanding of the universe and one of its most enduring mysteries.
Lieu’s recent study, “The binding of cosmological structures by massless topological defects,” appeared in Monthly Notices of the Royal Astronomical Society.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.