A University of Cincinnati physicist and an international team of collaborators say they have worked out a theoretical method for producing axions inside fusion reactors. It is a challenge that even two well known fictional physicists could not solve on television.
On the CBS sitcom "The Big Bang Theory," characters Sheldon Cooper and Leonard Hofstadter wrestled with the same idea across three episodes in Season 5. Despite their efforts, the problem remained unsolved in the show.
Now UC physics professor Jure Zupan and his co authors from the Fermi National Laboratory, MIT and Technion-Israel Institute of Technology report a possible solution. Their findings appear in a new study published in the Journal of High Energy Physics.
Why Axions Matter to Dark Matter Research
Axions are theoretical subatomic particles that scientists believe could help explain dark matter. Dark matter is of intense interest because it plays a major role in shaping the universe after the Big Bang nearly 14 billion years ago.
Although dark matter has never been detected directly, physicists think it makes up most of the matter in the universe. Ordinary matter, including stars, planets and people, accounts for only a small fraction. Dark matter earns its name because it does not absorb or reflect light.
Its presence is inferred through gravity. The unusual motions of galaxies and the stars within them suggest that large amounts of unseen matter are exerting gravitational pull. One leading idea is that dark matter consists of extremely light particles known as axions.
Fusion Reactors as a Source of New Particles
In their study, Zupan and his colleagues examined a fusion reactor design that uses deuterium and tritium fuel inside a lithium lined vessel. This type of reactor is being developed through an international collaboration in southern France.
Such a reactor would generate vast numbers of neutrons along with energy. According to the researchers, those neutrons could also lead to the creation of particles linked to the dark sector.
"Neutrons interact with material in the walls. The resulting nuclear reactions can then create new particles," he said.
Another possible production route occurs as neutrons collide with other particles and slow down. This process releases energy in a phenomenon known as bremsstrahlung, or "braking radiation."
Through these mechanisms, the reactor could theoretically produce axions or axion like particles. Zupan noted that this is where the fictional physicists on television came up short.
The Big Bang Theory Easter Egg Explained
"The Big Bang Theory" aired from 2007 to 2019, won seven Emmys and remains one of the most watched shows on streaming platforms, according to Nielsen.
"The general idea from our paper was discussed in 'The Big Bang Theory' years ago, but Sheldon and Leonard couldn't make it work," Zupan said.
In one episode, a white board displays an equation and diagram that Zupan said represent how axions are produced in the sun. In a later episode, a different equation appears on another board. Under the calculations, drawn in a different marker color, is a clear sad face -- a visual sign of failure.
Zupan explained that the equation compares the chances of detecting axions from a fusion reactor with those coming from the sun -- and the comparison is not encouraging.
"The sun is a huge object producing a lot of power. The chance of having new particles produced from the sun that would stream to Earth is larger than having them produced in fusion reactors using the same processes as in the Sun. However, one can still produce them in reactors using a different set of processes," he said.
The show never explicitly mentions axions or explains the white boards. These details serve as inside jokes for scientists, fitting a series known for weaving concepts like Schrodinger's cat and the Doppler effect into its plots, along with appearances by Nobel Prize winners and "Star Trek" alumni.
"That's why it's fantastic to watch as a scientist," Zupan said. "There are many layers to the jokes."
