Charm and Anticharm—Not Quite the Same

From what we can observe, there is no symmetry between matter and antimatter in the Universe. All structures, from unimaginably large clusters of galaxies to microscopic human cells, are made of matter: protons, neutrons, and electrons. Though it is possible to produce antimatter—antiprotons, antineutrons, and positrons—in high-energy particle collisions, and even make medical use of positrons, antimatter seems to have disappeared from the Universe at large.