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Two major mysteries in science, the nature of dark matter and the possible existence of higher dimensions, could be linked, new research suggests. The team behind a new study proposes that dark matter may be so strange and ghost-like because it is in tune with a fifth dimension.
When scientists discuss "extra dimensions," they aren't talking about other universes in which another evil version of you exists (and with a beard). Instead, they refer to dimensions that could be "curled up" with reality alongside the standard four-dimensional spacetime , consisting of the three dimensions of space and one dimension of time.
While these extra dimensions remain highly speculative, they have become a hot topic, especially as string theory, the most popular extension to standard physics, relies upon the existence of at least 11 dimensions. Scientists are more sure that dark matter exists, but proving its existence still remains troubling because, despite its gravity literally holding galaxies together and outweighing ordinary matter by around five to one, it remains effectively invisible because it doesn't interact with light and it simply ghosts through ordinary matter.
"Understanding dark matter would represent a profound advance in humanity's knowledge of the cosmos and what it is made of," team member Yu-Dai Tsai of the University of Sheffield said in a statement .
"Our research gives physicists clear new targets in the search for dark matter, while connecting two of the biggest ideas in fundamental physics: the mystery of dark matter and the existence of hidden dimensions."
Dark photons play dark matter like a violin
Though the main idea is that dark matter may operate in the fifth dimension, this new research expands upon that concept with another theory. It suggests that dark matter exists with another inhabitant of the fifth dimension, a force-carrying particle called a "dark photon."
Standard photons are the constituent particles of electromagnetic radiation, or light; dark photons would be similar but for a hypothetical "dark force."
The team's new proposal would see the unique geometry of the fifth dimension causing the masses of dark matter particles to form an arrangement that gives rise to a "dark matter resonance." This is akin to the intense vibration of a musical instrument at certain notes.
"Dark matter resonance is already known to be a powerful idea, with the potential to change our understanding of how dark matter was produced in the early universe and how we search for it today," team member Yu-Dai Tsai of the University of Sheffield said in a statement. "But many previous resonant dark matter models have treated the resonance as an assumption. This work gives a possible deeper origin for it: the resonance may come directly from the geometry of hidden dimensions."
An illustration shows a cloud of dark matter slipping past a distant star (Image credit: Robert Lea (created with Canva)) Tsai explained that while dark matter resonance is a phenomenon that has been explored before, the research conducted by this team differs because it suggests dark matter resonance is not a coincidence. Instead, the possible deeper origin for the resonance sees it emerge directly from the geometry of hidden dimensions. This would allow dark matter to interact strongly shortly after the Big Bang while allowing it to settle into its ghost-like inert existence today.
"This resonance can make dark matter interactions much stronger at crucial epochs in cosmic history, such as in the early universe," Tsai added. "Crucially, the model allows for these strong interactions in the past while still explaining why dark matter appears so inert and hard to detect today."
Of course, it is very early days for the team's theory, but it excitingly offers a way toward solving two of the universe's greatest mysteries.
The team's research was published in the Physical Review D.
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