Gravity Without Mass: UAH Study Proposes Alternative to Dark Matter

A new study by Dr. Richard Lieu of The University of Alabama in Huntsville (UAH) challenges our understanding of gravity, potentially offering an alternative explanation for dark matter. The research, published in Monthly Notices of the Royal Astronomical Society, proposes a theory of gravity that can exist independently of mass.

Dark matter—a hypothetical type of matter implied by gravitational effects—cannot be described by general relativity unless there is more matter in the universe that can be seen. The theory was initially proposed by Dutch astronomer Jan Oort in 1932 to explain the so-called “missing mass” required for things like galaxies to cluster together. However, this theory is still as unresolved today as over a century ago.

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—which gives a finite gravitation force in the absence of any detectable mass. This initiative is, in turn, driven by my frustration with the status quo, namely the notion of dark matter's existence despite the lack of any direct evidence for a whole century.

Richard Lieu, Distinguished Professor, Department of Physics and Astronomy, The University of Alabama in Huntsville

According to the researcher, concentric sets of shell-like topological defects in structures commonly found throughout the universe could be the source of the "excess" gravity required to hold a galaxy or cluster together.

These defects were most likely created during the early universe when a phase transition occurred. A physical event known as a cosmological phase transition occurs when the general state of matter changes simultaneously throughout the universe.

Lieu added, “It is unclear presently what precise form of phase transition in the universe could give rise to topological defects of this sort. 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 2-D structures such as spherical shells are also possible. 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.”

Gravitational force, which ultimately includes the warping of space-time itself, allows all objects to interact with one another, regardless of mass. Massless photons, for example, have been shown to feel gravitational effects from astronomical objects.

Lieu noted, “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. 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.”

He added, “Both the deflection of light and stellar orbital velocities is the only means by which one gauges the strength of the gravitational field in a large-scale structure, be it a galaxy or a cluster of galaxies. The contention of my paper is that at least the shells it posits are massless. There is then no need to perpetuate this seemingly endless search for dark matter.”

Future research questions will likely focus on how these shells coordinate to create a galaxy or cluster, as well as how the structures evolve.

Lieu concluded, “This paper does not attempt to tackle the problem of structure formation. A contentious point is whether the shells were initially planes or even straight strings, but angular momentum winds them up. There is also the question of how to confirm or refute the proposed shells by dedicated observations. Of course, the availability of a second solution, even if it is highly suggestive, is not by itself sufficient to discredit the dark matter hypothesis - it could be an interesting mathematical exercise at best. But it is the first proof that gravity can exist without mass.”

Journal Reference:

Lieu, R., (2024) The binding of cosmological structures by massless topological defects. Monthly Notices of the Royal Astronomical Society. doi:10.1093/mnras/stae1258