Can something be its own opposite?
Yeah, Batman knows a thing or two about this.
You remember the story: Heroic attorney Harvey Dent suffers horrible burns on 50 percent of his body, and his mind snaps. An evil, criminal persona rises to the surface, and he becomes Two-Face, the coin-obsessed maniac with ridiculous taste in half-and-half clothing.
Particle physicists also have a paradoxical two-face in their rogues gallery: the Majorana fermion, a particle that act as its own antiparticle.
Let's refresh. According to the standard model, particles and quasi particles fall into two categories: fermions and bosons. The fermion camp includes quarks and leptons like electrons, among others. We call these Dirac fermions. Here you'd find negatively charged electrons squaring off with antiparticle counterparts called positrons, which pack a positive charge. When these particles come in contact with each other, they annihilate each other.
That's exactly the sort of duality Two-face would appreciate. The coin has two sides, and it's either one or the other, heads or tails. Slip him a two-headed coin or something and it drives him up the wall.
The boson camp includes the photons that make up light; these brilliant particles are their own antiparticles, producing a thoroughly neutral charge. Really, you expect this sort of thing from a boson.
But is such a thing possible in the fermion camp? Back in the 1930s, physicists predicted it was, but no one ever actually spotted a so-called Majorana fermion. In 2012, a team of Dutch particle physicists indirectly detected these tiny two-faces in lab experiment, but this falls short of an official confirmation that they exist.
Once we catch the experimental evidence, however, exciting things may occur. Majorana fermions would boast a unique ability to "remember" past positions in reference to each other, making them very useful in the realm of quantum computing. One theory even holds that all the dark matter in the universe is actually made up of Majorana fermions.
Dark matter computers. Just think about that for a moment.