Anti-Matter
From Multiversal Omnipedia
Anti-matter is matter which is composed of atoms that have the opposite charge of normal matter (electrons in place of positrons and vice versa). Anti-matter reacts with normal matter on contact, releasing a great amount of energy as the two annihilate one another. It can be manufactured, but the process is extraordinarily intensive. It has been theorized that entire universes of anti-matter may exist on the other side of a black hole.