For decades, you have heard scientists say that most of the universe is missing. They are not being dramatic. They mean it in a literal sense.
A huge share of matter in the cosmos cannot be seen or touched, yet its pull shapes galaxies and bends light. If you live with an illness that seems to have no clear cause or if you have ever wondered why so much of nature hides behind a curtain, this idea may feel strangely familiar. Physicists feel that same frustration. They know dark matter must be real, but the particles that might make it up have stayed quiet.
Why Tiny Forces Matter
Some of the most promising dark matter candidates are ultralight exotic bosons, such as axions and dark photons. These particles might form halos across the universe or create faint interactions with ordinary matter. Those tiny interactions could shift atomic energy levels in ways your senses would never notice, but quantum sensors can. These sensors track changes in spin, a property of particles that behaves like a tiny compass needle.
Schematic of space-based search for ultralight exotic bosons and the prototype space quantum sensor, including vapor cell, magnetic shield, fiber-optic gyroscope, and radiation shielding box. (CREDIT: National Science Review)
Experiments on Earth have tried to detect these unusual interactions, but the limits of the planet work against you. If a lab wants a stronger signal, it needs more polarized spins in the source, or it needs the source to move much faster. Faster motion boosts the effect, yet anything heavy enough to hold many spins moves slowly. The trade-off is unavoidable. Even the best spin sources with polarized electrons crawl along at about 20 meters per second. The result is that huge regions of theoretical space remain untouched.
If you picture how slow healing can feel, or how a diagnosis may hinge on the faintest sign in lab data, you may understand the emotional tug behind this scientific challenge. Researchers feel the weight of the unknown, too.
Why Space Changes the Odds
This struggle pushed physicists to think beyond Earth. Their solution is the Space-based Quantum Sensing for Interaction and Exotic Bosons Research Exploration, known as SQUIRE. The plan sounds bold. Install quantum spin sensors on space stations and let the sensors race around Earth at orbital speed. The China Space Station moves at 7.67 kilometers per second. That is almost 400 times faster than anything a lab can push across a table.
Concept of the space-based searches for exotic bosons. (CREDIT: arXiv)
Then there is Earth itself. The planet holds an immense supply of unpaired electrons inside its mantle and crust. These geoelectrons sit under the influence of Earth’s magnetic field and act as a natural polarized spin source far larger than anything humans can engineer. When the station orbits, its motion turns any exotic signal into a slow periodic wave. The signal drops to about 0.189 millihertz, a range where noise is very low. Instead of fighting interference, the station glides into a quieter part of the spectrum.
With these advantages, simulations show exotic field strengths that can reach 20 picotesla. That is far above the limits seen on Earth. With 100 days of measurements and careful tuning, SQUIRE could improve sensitivity by six or seven orders of magnitude for certain interaction ranges. Matching that on the ground would require speeds faster than light. Even the boldest physicist knows that is impossible.
Building a Sensor That Survives Space
To turn this idea into a real experiment, the team built a prototype space sensor designed for long missions and constant radiation exposure. A sensor in orbit faces three big problems. The geomagnetic field shifts in time and space. The station vibrates. Cosmic particles strike the equipment dozens of times a day.
The engineers answered these issues with three key technologies. They built a dual noble-gas system using isotopes of xenon that have opposite gyromagnetic ratios. This pairing cancels shared magnetic noise and keeps the sensor tuned to the exotic signal. Together with multiple layers of shielding, the system drops noise to below 0.02 femtotesla.
Design diagram of prototype space quantum sensor. (CREDIT: National Science Review)
A fiber-optic gyroscope corrects for vibration and reduces those effects to 0.65 femtotesla. A tough aluminum shell and redundant control circuits keep the device running even when radiation takes out part of the system. These steps cut disruptions to about one a day.
The final result is a prototype that reaches a sensitivity of 4.3 femtotesla in a single measurement lasting just over 19 minutes. That timing fits the 1.5-hour orbital cycle and offers a clear path to collecting high-quality data.
What a Space-Based Network Could Do
The SQUIRE team sees this as only the beginning. The long-term vision is a space-ground network of quantum sensors that work together. Such a network could test several dark matter models at once. It could also explore axion halos, violations of fundamental symmetries, and other physics that push against the limits of the Standard Model.
Orbital motion increases how strongly axion halos couple to the spins of particles such as nucleons. This boost could make the search ten times more sensitive. As deep space missions grow, sensors placed near gas giants like Jupiter or Saturn could make use of their abundant polarized particles. Worlds that once seemed far away could become tools for exploring hidden forces.
Practical Implications of the Research
This work opens the door to a new way of studying nature. If ultralight bosons exist, they could connect dark matter to ordinary matter in a way that finally explains the invisible mass in the universe. A space-based sensor network could give physicists the first direct look at these particles and help shape the next version of particle physics.
The results would ripple across cosmology, high-energy physics, and even technology. Advances in quantum sensing often lead to better medical imaging, navigation tools, and environmental monitors.
The emotional value is harder to measure. When you feel lost in uncertainty, any step toward understanding the unseen can offer comfort. That same comfort drives this search for the universe’s hidden matter.
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