Wild new study suggests gravity may exist without mass

What is massless gravity? Both Newton’s revolutionary laws describing its universal effect and Einstein’s proposal of a deflated spacetime, we have thought of gravity as exclusively within the realm of matter.

Now a wild new study suggests that gravity can exist without mass, conveniently eliminating the need for one of the most elusive substances in our Universe: dark matter.

Dark matter is a hypothetical, invisible mass thought to make up 85 percent of the total mass of the Universe. Originally designed to account for galaxies held together under high-speed rotation, it has yet to be observed directly, prompting physicists to propose all sorts of ideas to avoid invoking this elusive material as a way to close the holes in current theories.

The latest offering in this regard comes from astrophysicist Richard Lieu at the University of Alabama in Huntsville, who has suggested that instead of dark matter binding galaxies and other bodies together, the Universe may contain thin, shell-like layers of ‘topological defects’ that give rise to gravity without any fundamental mass.

Lieu began trying to find another solution to Einstein’s field equations, which relate the curvature of spacetime to the presence of matter within it.

As Einstein described in his 1915 theory of general relativity, spacetime warps around bundles of matter and streams of radiation in the Universe, depending on their energy and momentum. This energy is, of course, related to mass in Einstein’s famous equation: E=mc².

So the mass of an object is related to its energy, which bends space-time – and this bending of space-time is what Einstein described as gravity, a level more sophisticated than Newton’s approximation of gravity in the century 17th as a force between two objects with mass. . In other words, gravity seems inextricably linked to mass.

Not so, thinks Lieu.

In his work, Lieu attempted to solve a simplified version of Einstein’s field equations that allows for a finite gravitational force in the absence of any discernible mass. He says his efforts were “fueled by my frustration with the status quo, namely the notion of the existence of dark matter despite the lack of any direct evidence for an entire century.”

The Lieu solution consists of shell-shaped topological defects that can occur in very compact regions of space with a very high matter density.

These groups of concentric shells contain a thin layer of positive mass embedded within an outer layer of negative mass. The two masses cancel each other out, so the total mass of the two layers is exactly zero. But when a star lies in this shell, it experiences a huge gravitational force pulling it towards the center of the shell.

“The contention of my paper is that at least the shells it presents are without mass,” says Lieu. If these controversial suggestions carry any weight, “then there is no need to perpetuate this seemingly endless search for dark matter,” Lieu adds.

The next question, then, is how the shells that Lieu has proposed can be confirmed or refuted through observations.

“The increasing frequency of observations of ring and shell galaxy formation in the Universe provides evidence for the type of source proposed here,” Lieu writes in his paper. Although he admits that his proposed solution is “very suggestive” and cannot discredit the dark matter hypothesis alone.

“It can be an interesting mathematical exercise at best,” Lieu concludes. “But it is the first [mathematical] proof that gravity can exist without mass.”

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