Quantum mechanics has long classified particles into just two distinct types: fermions and bosons. Now, physicists at Rice University in the US have discovered that a third type may be possible after all, at least mathematically speaking. Known as paraparticles, their behavior could imply the existence of elementary particles that no one had ever considered.
“We determined that new types of particles that we had never known before are possible,” says Kaden Hazzard, who, with co-author Zhiyuan Wang, formulated a theory to demonstrate how objects that were neither fermions nor bosons could exist in physical reality without breaking any known laws.
Fermions include fundamental particles that ‘build’ atoms, such as electrons and quarks. More precisely, they have a property that prevents them from occupying identical quantum states, effectively ensuring that no two corresponding fermions can fill the same space.
“This behavior is responsible for the entire structure of the periodic table,” says Hazzard. “It’s also why you don’t pass through your chair when you sit down.”
Bosons are defined by a different measure of this property that allows them to pass through each other like ghosts in a hallway.
Typically acting as force carriers, like photons and gluons, bosons mediate interactions in ways that push and pull fermions into everything from protons to porcupines to potatoes to planets.
There is one notable exception to this strict rule of quantum state segregation. Restricted to just two dimensions, some materials can give rise to particle-like behavior that breaks the expected statistical laws of fermions and bosons, effectively allowing a one-time exchange of quantum states.
Known as anyons, these technical loopholes cannot extend into the three-dimensional space of our Universe and are therefore unlikely to be represented by any genuine fundamental particles we have yet to discover. One less new hallway in quantum hardware; they’re more like a novelty keychain you can pick up at the front counter.
Still, that’s never stopped theoretical physicists from tinkering with quantum descriptions of hypothetical particles to see what survives, operating in a field called parastatistics. While it’s a purely mathematical act of expression, doing so can reveal deeper truths about whether fermions and bosons are really all there is, and if so, why.
Since its inception in the early to mid-20th century, parastatistics has failed to find anything that couldn’t fall into either the fermion or boson boxes. Indeed, as quantum theories have developed over time, it has become increasingly clear that any theory developed through parastatistics would be indistinguishable from a universe with only fermions and bosons.
Wang and Hazzard think they have found a reason to disagree. By introducing a second quantization step distinct from previous methods, they have shown that collective behaviors in materials can give rise to particles that act in some way like anyons, even when turning corners in a three-dimensional universe more or less identical to our own.
The concept falls far short of mapping a path to an entirely new class of particles, and only serves to show that we may not want to close the door on this possibility just yet.
“To realize paraparticles in experiments, we need more realistic theoretical proposals,” says Wang.
However, knowing the hardware of the Standard Model of quantum physics still provides nothing for general relativity and has no room for dark matter bricks or the equally mysterious sources of dark energy, so having plans for expansion is worthwhile.
