For years, one of the most intriguing mysteries in physics has been dark matter—an invisible substance thought to make up most of the matter in the universe.
Now, a group of real-life physicists say they’ve solved a problem that even two famous fictional scientists couldn’t crack on television, and their work could help scientists search for dark matter in a surprising place: fusion reactors.
In the sitcom The Big Bang Theory, physicists Sheldon Cooper and Leonard Hofstadter spend several episodes wrestling with a theoretical challenge: how to produce exotic subatomic particles called axions using a fusion reactor.
Despite pages of equations and intense debates, they never succeed. A sad face drawn on a whiteboard marks their failure.
Now, physicist Jure Zupan from the University of Cincinnati, along with colleagues from Fermi National Accelerator Laboratory, Massachusetts Institute of Technology, and Technion – Israel Institute of Technology, believes they’ve found a way forward.
Their theoretical solution was published in the Journal of High Energy Physics.
Axions are hypothetical particles that scientists think may make up dark matter. Dark matter has never been seen directly, but its gravitational effects are clear. It influences how galaxies move and how the universe evolved after the Big Bang nearly 14 billion years ago.
Although normal matter—stars, planets, people—makes up everything we can see, it accounts for only a small fraction of the universe’s total matter. The rest, physicists believe, is dark matter.
One leading idea is that dark matter consists of extremely light particles like axions. These particles would rarely interact with ordinary matter, which makes them incredibly difficult to detect. That’s why physicists are always looking for new ways to produce or observe them.
In their study, Zupan and his colleagues explored what might happen inside a large fusion reactor like the one being built in southern France. This reactor uses deuterium and tritium—forms of hydrogen—to produce energy, much like the reactions that power the sun. But unlike the sun, the reactor is surrounded by walls lined with lithium and bombarded by an intense flood of neutrons.
Those neutrons turn out to be the key. When neutrons collide with materials in the reactor walls, they can trigger nuclear reactions that may produce new particles. In addition, as neutrons slow down by bouncing off other particles, they release energy in a process called bremsstrahlung, or “braking radiation.”
According to the researchers’ calculations, these processes could produce axions or axion-like particles.
This is where the fictional physicists went wrong. Sheldon and Leonard assumed that axions in a reactor would be produced in the same way they are generated in the sun. Since the sun is vastly larger and more powerful, the math showed reactors had little chance of competing. That’s why the equation on the show ended with a sad face.
“The sun is enormous and produces a huge number of particles,” Zupan explained. “So if you only use the same processes as in the sun, reactors look hopeless. But reactors allow for different processes that don’t occur in stars.”
Those alternative processes are what make fusion reactors interesting as potential sources of dark matter particles. While the work remains theoretical, it offers a new way to think about how axions might be created and detected in controlled environments on Earth.
The connection to a popular TV show is more than a fun coincidence. The Big Bang Theory is known for hiding real physics inside jokes, equations, and background props. Although the characters never mention axions directly, the whiteboard equations were a quiet nod to real debates happening in the physics community.
“That’s what makes the show so enjoyable for scientists,” Zupan said. “There are layers to the humor that most people never notice.”
While Sheldon and Leonard never solved their problem, real-world physicists may now be one step closer—bringing us closer to understanding dark matter and the hidden structure of the universe.
