A new study by Dr. Richard Lieu of The University of Alabama in Huntsville (UAH) challenges our understanding of gravity and potentially offers an alternative explanation for dark matter. The research, published in Monthly Notices of the Royal Astronomical Societyproposes a theory of gravity that can exist independently of mass.
Dark matter—the 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 originally proposed by Dutch astronomer Jan Oort in 1932 to explain the so-called “missing mass” needed for things like galaxies to clump together. However, this theory remains as unresolved today as it was more than a century ago.
My own inspiration came from my quest to further solve the gravitational field equations of general relativity—a simplified version of which, applicable to galaxy and galaxy cluster conditions, is known as Poisson’s equation—which gives the finite gravitational force in the absence of any detectable mass. This initiative, in turn, is driven by my frustration with the current state of affairs, specifically the notion of the existence of dark matter despite the lack of any direct evidence for a 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 needed 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 currently unclear what exact form of phase transition in space could lead to topological defects of this kind. Topological effects are very compact regions of space with very high matter density, usually in the form of linear structures known as cosmic strings, although 2D structures such as spherical shells are also possible. The shells in my paper consist of a thin inner layer of positive matter and a thin outer layer of negative matter; the total weight of both layers – which is all that can be measured in terms of weight—is exactly zero, but when the star lies on this shell it experiences a large gravitational force pulling it towards the center of the shell.”
Gravitational force, which ultimately involves warping space-time itself, allows all objects to interact with each other, regardless of mass. For example, massless photons have been shown to experience gravitational effects from astronomical objects.
Lieu noted:Gravitational bending of light by a set of concentric singular shells comprising a galaxy or cluster is caused by a beam of light being deflected slightly inward—that is, toward the center of the large-scale structure or set of shells.—as it passes through one shell. The overall effect of going through many shells is a finite and measurable total deflection, which mimics the presence of large amounts of dark matter in much the same way as the velocity of stellar orbits..”
He added, “Both the deviation of light and stellar orbital velocities are the only means by which to measure the strength of the gravitational field in a large-scale structure, be it a galaxy or a cluster of galaxies. The claim of my paper is that at least the shells it assumes are massless. There is no need to perpetuate this seemingly endless search for dark matter.”
Future research questions are likely to focus on how these shells coordinate to form a galaxy or cluster, as well as how the structures evolve.
Lieu concluded: “This article does not attempt to solve the problem of structure creation. A point of contention is whether the shells were originally planar or even straight strings, but angular momentum winds them up. There is also the question of how to confirm or disprove the proposed shells with specialized observations. Of course, the availability of the second solution, while highly suggestive, is not in itself enough to discredit the dark matter hypothesis—it could be an interesting mathematical exercise at best. But it is the first evidence that gravity can exist without matter.”
Link to the magazine:
Lieu, R., (2024) Binding of cosmological structures by immaterial topological defects. Monthly Notices of the Royal Astronomical Society. doi:10.1093/mnras/stae1258