'Paraparticles' Would Be a Third Kingdom of Quantum Particle

Summary

When you swap two paraparticles, these hidden properties change in tandem. As an analogy, imagine that these properties are colors. Start with two paraparticles, one that’s internally red and another that’s internally blue. When they swap places, rather than keeping these colors, they both change in corresponding ways, as prescribed by the mathematics of the particular model. Perhaps the swap leaves them green and yellow. This quickly turns into a complex game, where paraparticles affect each other in unseen ways as they move around. Meanwhile, Müller was also busy rethinking the DHR theorems. “It’s not always super transparent what they mean, because it’s in a very complicated mathematical framework,” he said. His team took a new approach to the paraparticle question. The researchers considered the fact that quantum systems can exist in multiple possible states at once — what’s called a superposition. They imagined switching between the perspectives of observers who exist in these superposed states, each of whom describes their branch of reality slightly differently. If two particles are truly indistinguishable, they figured, then it won’t matter if the particles are swapped in one branch of the superposition and not in the other. “Maybe if the particles are close by, I swap them, but if they are far away I do nothing,” Müller said. “And if they’re in a superposition of both, then I do the swapping in one branch, and nothing in the other branch.” Whether observers across branches label the two particles in the same way should make no difference. This stricter definition of indistinguishability in the context of superpositions imposes new restrictions on the kinds of particles that can exist. When these assumptions hold, the researchers found that paraparticles are impossible. For a particle to be truly indistinguishable by measurement, as physicists expect elementary particles to be, it must be either a boson or fermion. Although Wang and Hazzard published their pa...