Lets talk antimatter.
What is this material that seems to be hiding from detection? Most of the material on earth seems to be made of matter rather than antimatter. If antimatter-dominated regions of space existed, the gamma rays produced in annihilation reactions along the boundary between matter and antimatter regions would be detectable.
Antiparticles are created in the universe when high-energy particle collisions take place. Small quantities of antimatter are produced when High-energy cosmic rays impact Earth's atmosphere as particle jets, which are immediately annihilated by contact with matter. This stuff is awesome.
Physicists are closing in on how matter differs from antimatter