In 1998 scientists discovered that the universe is not only expanding but that its expansion is accelerating.
This totally unexpected behavior has been called the "most profound problem" in physics, because our current understanding of gravity says that attractions between mass in the universe should be causing the expansion to slow down.
The leading theory to explain the accelerating expansion is the existence of a hypothetical repulsive force called dark energy.
But in the new study, Massimo Villata, an astrophysicist at the Observatory of Turin in Italy, suggests the effects attributed to dark energy are actually due to a kind of "antigravity" created when normal matter and antimatter repel one another.
"Usually this repulsion is ascribed to a mysterious dark energy that would uniformly permeate the cosmos, but nobody knows what it is nor why it behaves this way," Villata said in an email.
"We are replacing an unknown force caused by an unknown element with the repulsive gravity of the well-known antimatter."
According to Villata, the keys to accelerated expansion lie in large-scale voids that are seen scattered throughout the cosmos.
These holes in our map of the universe—which can each be millions of light-years wide—are inexplicably empty of galaxies and galaxy clusters. The nearest hole to us is called the Local Void, bordering the Virgo supercluster of galaxies.
Villata thinks these voids harbor vast quantities of antimatter, which could even be organized into antimatter galaxies, complete with antimatter stars and planets.
All this antimatter doesn't emit radiation that can be detected by current sensors, making it effectively invisible, Villata said.
"There can be various reasons why antimatter in voids should be invisible, but we do not know which of them is the right one," Villata said. "Moreover, antimatter in laboratories could have different behavior, since it is 'immersed' in a world of matter."
While we can't see antimatter superstructures, we can observe their effects on our visible universe, Villata argues, because antimatter must repel the normal matter in galaxies, pushing them farther from one another.
Villata says his theory, which will appear in an upcoming issue of the journal Astrophysics and Space Science, has the potential to solve other cosmic mysteries, such as the universe's "missing antimatter" problem.