Here's What Scientists Know About The Portal To The Fifth Dimension

One of the biggest unsolved problems in astrophysics is the existence of dark matter. Since the 1930s, the mysterious matter has been proven to exert its gravitational forces on the cosmos time and time again. Dark matter is estimated to compose 75% of all the matter in the universe, and it may have even existed before the Big Bang. Without dark matter, galaxies would be ripped apart by their own rotational forces, the gravitational lensing observed by space telescopes and predicted by Albert Einstein would be impossible, and the structure of the "cosmic web" would collapse. It's clearly an important feature of our universe, which is why dark matter's elusive nature is so frustrating. Thankfully, after a century of searching, scientists may finally be honing in on identifying the universe's most abundant type of matter.

In 2021, a team of European theoretical physicists published an article in The European Physical Journal titled, "A warped scalar portal to fermionic dark matter." The paper built upon a 1999 proposal that dark matter could be explained by incorporating dimension-traveling particles, called fermions, into our model of space-time. The math is complicated, but at its most basic level, these theoretical fermions could be popping in and out through fifth-dimensional "warped space" portals and influencing the gravitational fields of galaxies. The model would explain the phenomena attributed to dark matter.

The biggest obstacle in verifying the theory is the difficulty in observing such "higher-dimensional particles." Fermionic dark matter that slips between five dimensions isn't exactly something you can see with a keen eye. However, there's still hope. Modern physicists have made huge strides in constructing gravitational wave detectors, which can be used to observe ripples in spacetime. Such instruments may also be able to detect cross-dimensional fermions and determine if their behavior explains dark matter.

Fermions are the best candidates for dark matter because they are matter. Fermions are the class of particles that encompasses everything we typically think of as having mass: protons, neutrons, electrons, and their counterparts. And with mass, comes gravity. In 2012, scientists at CERN announced the groundbreaking discovery that the Higgs-Boson particle was real, proving that mass arises from fermion particles' interactions with the Higgs field. This discovery provided scientists with more than just a step towards a quantum theory of gravity — it also suggested the presence of a fifth dimension.

Without getting into the weeds of complex theoretical physics, the confirmation of the Higgs-boson opened up a can of worms. Its discovery was irrefutable, yet it also revealed holes in the standard model of particle physics. One such hole surrounds explaining certain traits of the Higgs field's behavior, which, taken at face-value, seems to defy the four fundamental forces and the standard model of particle physics. Many physicists sought to rectify the disparity. Doing so required introducing a fifth dimension into the standard model — conservationists propose that the Higgs field's behavior is actually a consequence of the weak force acting through higher dimensions.

So far, dimensions beyond our known four (three dimensions of space plus one dimension of time) have not been proven. Nonetheless, proof of a fourth spatial dimension could resolve many outstanding problems in physics, including dark matter. For instance, it could explain why gravity is so weak, why gravitational bonds can seemingly defy the speed of causality (i.e. the speed of light), and why spiral galaxies don't whip their stars into the great beyond. Such revelations could revolutionize our understanding of physics, so we'll keep waiting for the next generation of gravitational wave detectors to find out.

Calling your research article, "A warped scalar portal to fermionic dark matter" requires some serious mathematical proofs to substantiate. In 2021, the European team behind the article presented a robust explanation for how a fifth dimension could exist, and, more pressingly, how massive fermion particles could potentially pass through it. As with so much of theoretical physics, the proof would require some of the most advanced testing procedures ever conceived to validate — some of which haven't even been invented. Indeed, to confirm the theory would demand proof of a totally unconfirmed dimension never before touched by experimental physics. 

According to the article, this new proposed scalar field would exhibit "interesting" behavior that, in simple terms, sucks up fermions and carries them to sporadically fifth-dimensional locations for nearly instantaneous moments. Such random slips between dimensions could explain how greater gravitational forces are experienced by galactic centers. The sudden appearance of a massive particle in a random location could enact a brief, minor gravitational force on the surrounding matter, even if its appearance was extremely short-lived. The authors describe such a particle as an "author" of dark matter, one unbounded by the constraints of fourth-dimensional causality (i.e. the speed of light). 

Frustratingly, a particle teleporting across space-time via the fifth dimension would be extremely difficult to detect. If the fifth dimension allows particles to slip across spatial dimensions without adhering to the constraints of space-time causality, their sudden apparition and disappearance would be virtually ghostlike. Thus, the proposal raises a conundrum nearly impossible to confirm without the most sensitive particle detectors ever conceived. We might be in an era of extremely precise theoretical physics, but dimension-slipping particles are, for the time being, a vast leap beyond our experimental capabilities.