In a recently published study, particle physicists at the University of California Riverside theorize that dark matter could be explained by the existence of a new dimension in space-time.
In astrophysics, the dark matter it is a (still theoretical) form of matter that makes up about 85% of the matter in the universe. The existence of this invisible force is implied through a variety of observations in the universe, including gravitational effects that cannot be explained by accepted theories of gravity. Since dark matter does not appear to absorb, reflect or emit electromagnetic radiation, measuring or providing definitive evidence of its existence has so far been impossible.
The study of the fourth dimension
In a research paper published in the Journal of High Energy Physics, a team of physicists from UC Riverside say that the presence of a fourth dimension could explain the existence of dark matter and explain why it remains invisible.
“Our observed universe has three dimensions of space. We propose that there may be a fourth dimension. The extra dimension may explain why dark matter has hidden itself so well from our attempts to study it in the laboratory,” says Dr. Philip Tanedo, assistant professor of physics and astronomy at UC Riverside and co-author of the new study, in a press release.
The fourth dimension? A hunt that has lasted a long time
Before the hypothesis of a new dark dimension, the existence of invisible forces has been theorized for a long time.
It was first proposed by the mathematical physicist and engineer william thomson in 1884.
Thomson is also known as Lord Kelvin after being the first British scientist to be elevated to the House of Lords.
Thomson estimated that the mass of the Milky Way differed from the luminous mass of visible stars, concluding that "many of our stars, perhaps the great majority of them, are perhaps dark bodies."
In the following century, scientists have made numerous indirect observations supporting Thomson's proposed existence of “dark bodies,” or the presence of some type of invisible matter that plays a significant influence on the universe.
We don't see it, but we know it's there
The main evidence for the existence of an invisible force comes from calculations showing that galaxies would not form or move as they do without large amounts of invisible matter.
So far, scientists have been unable to directly detect dark matter, leading most physicists to conclude that the substance must be made up of non-baryonic particles or subatomic particles whose mass is less than that of a proton. The indirect evidence, however, has been strong enough to lead most of the scientific community to generally accept the existence of dark matter (and four dimensions, in fact: AT LEAST four).
“We live in an ocean of dark matter, yet we know very little about what it might be,” Tanedo said. “It is one of the most vexing known unknowns in nature. We know it exists, but we don't know how to look for it, or why it didn't show up where we expected it."
Could a 4th dimension explain dark matter?
In the new paper, Tanedo and his colleagues suggest that dark matter particles don't behave like particles.
“The goal of my research program over the past two years is to extend the idea of dark matter 'talking' to dark forces,” Tanedo said in the UC Riverside press release. “Over the past decade, physicists have realized that, in addition to dark matter, other hidden dark forces may govern dark matter interactions. Confirming their existence could completely rewrite the rules on how to search for dark matter.”
Tanedo reiterates that this operation of “dark forces” can be described mathematically by a theory that includes an additional fourth dimension.
Dark matter would appear as a continuous sequence of adjacent particles within this dark fourth dimension. This would explain how dark matter causes some of the curious behavior observed in small galaxies.
An extra dimension, a recurring idea
Although the existence of a new fourth dimension sounds sensational, Tanedo explained that extra-dimensions are simply a mathematical trick to describe even ordinary theories.
After all, the idea that existence is made up of one dimension, or rather many more extra-dimensions, is also commonly referred to in String Theory or that of the holographic universe.
Thinking in an unconventional way
Past examinations of dark matter have mainly focused on theories explaining behaviors similar to visible particles. Tanedo and his fellow researchers say their new approach to the fourth dimension explores new possibilities not considered before.
Ordinary forces can be described as a single type of particle with a fixed mass.
The proposed theory predicted that invisible particles can be described by an infinite number of different particles with different masses called continuums.
Different forces
The researchers say that the continuous force of these invisible particles would be very different from the forces felt by ordinary matter. “For the gravitational or electrical force that I teach in my introductory physics course, when you double the distance between two particles, you reduce the force by a factor of four. A continuous force, on the other hand, is reduced by a factor of up to eight,” Tanedo explained.
In the paper, UC Riverside physicists say they have discovered that a continuous force like the one proposed could replicate observations of stellar motions in the universe.
Next step, a “dark photon”
Tanedo's team says they plan to continue expanding their theory by exploring a "dark photon" model.
“It's a more realistic image for a dark force,” Tanedo said. “Dark photons have been studied in great detail, but our fourth-dimensional structure has some surprises. We will also examine the cosmology of dark forces and the physics of black holes."
