But now, a bold new idea is challenging this tidy system. Scientists at Rice University in Texas believe there may be a third kind of particle—one that doesn’t follow the rules of fermions or bosons. They’ve developed a mathematical model showing how these unusual entities, called paraparticles, could exist in real materials without breaking the laws of physics.

“We determined that new types of particles we never knew of before are possible,” says Kaden Hazzard, one of the researchers behind the study. Along with co-author Zhiyuan Wang, Hazzard used advanced math to explore this idea.

Their work, published in Nature, suggests that paraparticles might arise in special systems and act differently than anything scientists have seen before.