Dark matter, which is estimated to account for about 27% of the universe’s contents, has been proposed to exist in an unseen “hidden fifth dimension” beyond human perception. According to the theory, the unique geometry of this hidden dimension determines the properties of dark matter, and analysts say it could provide a framework for explaining why dark matter has remained undetected for nearly 90 years.
The University of Sheffield team announced on the 13th (local time) that it had published its findings in the international journal Physical Review D. The study was led by Dr. Yudai Chai, a Senior Research Fellow of the Dorothy Hodgkin Fellowship at the Royal Society.
The core idea is this: dark matter exists in a hidden dimension together with a particle called the “dark photon.” The geometry of this dimension aligns the masses of the two particles in a specific ratio, creating a “resonant” state. This resonance supposedly amplified dark matter interactions in the early universe, while today those conditions no longer hold, making the interactions much weaker.
Dark matter is one of the universe’s constituent substances confirmed only through its gravitational effects.
It does not emit or reflect light and has never been directly observed by any telescope. Yet the scientific community does not doubt its existence. The reason is gravity.
Stars in the outer regions of galaxies should, based on their observed orbital speeds, be flung out of their galaxies. The visible mass of stars and gas alone does not generate enough gravity to hold them in place.
In reality, galaxies remain intact. Calculations show that some unseen substance is providing additional gravitational pull. This is why scientists often compare dark matter to the “glue” that holds galaxies together.
Evidence has accumulated over time. In the 1930s, Swiss astronomer Fritz Zwicky first raised the issue through observations of galaxy clusters. In the 1970s, American astronomer Vera Rubin strengthened the case through measurements of galactic rotation speeds. Since then, dark matter has moved beyond the level of hypothesis and become part of standard cosmology. Gravitational lensing, in which large masses bend the light of background objects, as well as observations of the cosmic microwave background, also point to the same conclusion.
According to observations by the European Space Agency’s Planck satellite, ordinary matter such as stars and planets makes up only about 5% of the universe. Dark matter accounts for roughly 27%, and the rest is classified as dark energy. Dark energy is a separate mystery that accelerates the expansion of the universe and is distinct from dark matter.
Dark matter is considered to have played a key role in the formation of cosmic structures. The standard cosmological view holds that after the Big Bang, dark matter first clumped together through gravity to form a skeleton, and ordinary matter then gathered around it to form galaxies and stars. Understanding the properties of dark matter would change the precision of calculations on galaxy formation and cosmic evolution.
Its existence is confirmed, but its nature remains unknown. Despite 90 years of searching, no dark matter particle has ever been directly detected. It is regarded as one of the greatest unsolved problems in modern physics.
There have been candidate theories. For a long time, physicists have considered the heavy hypothetical particle known as a “WIMP” as the most promising candidate because it interacts only very weakly with ordinary matter. Ultra-light axions are also among the candidates. Dozens of experiments around the world have been designed to detect WIMPs, but no decisive evidence has been found. Even as detector sensitivity has improved dramatically over generations, the searchable parameter space has only become narrower, weakening the standing of the WIMP hypothesis.
Dark matter has also appeared frequently in popular culture. In Star Trek, it appears as a vortex that destroys planets, while in the fantasy novel series The Golden Compass, it appears as a substance called “Dust” that sustains the multiverse.
The Sheffield team approached this problem through the concept of “dimensions.” The world humans perceive is described in four dimensions: three spatial dimensions—length, width, and height—plus time. The new theory assumes that a fifth, unobservable dimension exists beyond that.
The idea of extra dimensions has long been a subject of physics research. In the 1920s, European physicists introduced a fifth dimension while attempting to unify gravity and electromagnetism, and modern string theory explains that extra dimensions are compactified to extremely small scales and therefore remain unobserved. In recent years, several studies have also examined the possibility that dark matter exists in extra dimensions.
This study adds a new element: dark matter exists in a hidden dimension together with a force-carrying particle called the dark photon. Just as the photon mediates electromagnetism, the dark photon is a virtual particle that mediates interactions between dark matter particles.
In physics, collections of unknown particles that interact only very weakly with ordinary matter are grouped under the concept of the “dark sector.” This theory assumes that the dark sector, made up of dark matter and dark photons, operates within an extra dimension.
According to the team’s calculations, the distinctive geometry of the hidden dimension precisely arranges the masses of dark matter and dark photons. When the masses of the two particles meet a specific ratio, a “dark matter resonance” occurs. The researchers compared this to an instrument resonating strongly when it hits the right note.
Dr. Chai said, “Dark matter resonance is a powerful concept that could transform our understanding of how dark matter was produced in the early universe and how to search for it today.”
The resonance idea itself already existed in previous theories. However, existing models could not derive the resonance conditions from within the theory. The matching of particle masses had to be assumed by researchers, a weakness known in physics as a “fine-tuning problem.”
The new theory handles this differently. It argues that the mass alignment is not an assumption or a coincidence, but something that naturally emerges from the mathematical structure of the hidden dimension. Dr. Chai said, “Many existing resonance models treat resonance as an assumption, but this study offers a deeper origin in which resonance can emerge directly from the geometry of a hidden dimension.”
The point targeted by this theory is a contradiction in dark matter research. According to standard cosmology, dark matter must have interacted strongly in the early universe in order to produce the amount observed today. Yet current detectors have not captured any interaction signals. Explaining both conditions with a single theory has remained a challenge.
Right after the Big Bang, the universe was in a high-temperature, high-density state. The standard scenario says that dark matter’s total abundance was determined in this environment, where particle creation and annihilation repeatedly occurred.
The resonance concept bridges this gap. The logic is that at a certain stage in the early universe, resonance conditions were met and interactions were greatly amplified, but as the universe expanded and cooled, the system moved out of resonance and interactions weakened.
The calculation suggests that collisions and annihilation among dark matter particles became active during the resonance period, and this process determined the amount of dark matter that remains today. In this framework, the current lack of detection does not contradict the theory.
This explanation also aligns with the situation facing experiments worldwide. Search methods are broadly divided into three categories: direct detection, which attempts to capture the moment a dark matter particle strikes an atomic nucleus using underground detectors; indirect detection, which looks for signals left by dark matter annihilation through astronomical observations; and collider experiments, which try to create dark matter artificially in particle accelerators. No decisive result has been obtained through any of these routes.
Most direct-detection experiments are conducted deep underground. The reason is that particles arriving from space at the surface can create noise in detectors, so thick bedrock is used as shielding. The U.S. LZ experiment searches for the moment liquid xenon detectors register a collision between a dark matter particle and an atomic nucleus. Similar experiments have been carried out at Italy’s Gran Sasso underground laboratory. Japan and China are also operating large underground facilities and have joined the competition to search for dark matter. No definitive signal has emerged.
Korean researchers are also taking part in the verification race. The COSINE-100 experiment, led by the Center for Underground Physics at the Institute for Basic Science, announced in September 2025 that a signal claimed for 25 years by Italy’s DAMA/LIBRA team to be evidence of dark matter was not actually caused by dark matter. DAMA had argued that the frequency of dark matter collisions varies seasonally as Earth orbits the Sun, producing an “annual modulation signal.” COSINE-100 analyzed six years of data using the same type of detector and published its conclusion in the international journal Science Advances that the signal was not due to dark matter.
In a situation where leading candidates are being ruled out one after another, analysts say the significance lies in the presentation of a theoretical framework that explains the lack of detection itself.
The researchers said the new theory provides experimental physicists with a clear target to search for.
If the masses of dark matter and dark photons are aligned in a specific ratio, the mass range that detectors should focus on and the sensitivity required can be narrowed. Because the theory specifies the expected interaction strength and mass arrangement if resonance conditions hold, experiments can prioritize that range in their searches.
Dr. Chai said, “Understanding dark matter would represent a major advance in humanity’s knowledge of what the universe is made of, and this study connects two major frontiers of fundamental physics: dark matter and hidden dimensions.”
Verification remains the challenge. There is precedent for mathematically consistent theories losing ground because experiments failed to confirm them. Supersymmetry, once considered a leading theory, lost support after particles predicted by it were not found in experiments at CERN’s Large Hadron Collider. Hidden-dimension theories will likewise depend on whether observable signals are found.
South Korea already has a strong experimental base. Yemi Lab, located 1,000 meters underground at Yemi Mountain in Jeongseon, Gangwon Province, is a large underground research facility completed in 2022. Built using a former iron mine shaft, it requires a 600-meter vertical elevator descent followed by nearly 800 meters along an inclined passage to reach the laboratory. By area, it is among the six largest such facilities in the world.
The Center for Underground Physics is preparing the next-generation COSINE experiment there with improved detection performance. At Yemi Lab, the AMoRE experiment, which seeks to determine the properties of neutrinos alongside dark matter searches, is also being conducted. Globally, only a small number of countries possess deep underground research facilities of their own. The target proposed by the new theory may ultimately be reflected in future experimental design.
Dark matter research is also notable for its spin-off technologies. Ultra-sensitive detectors developed to capture faint signals, cryogenic cooling, low-noise electronics, and quantum measurement technologies have all been applied in medical imaging, computing, and communications. Basic physics experiments and industrial technology development thus move forward in tandem.
Whether hidden dimensions exist is ultimately a matter for experiment. The current stage appears to be one in which theory proposes a target and experiments test it.