An alchemist belief applicated as an universal law, theorized by Izumi Curtis and passed down to her students, the Elric brothers.
"The Universe is the All, and you are the One. All's existence and ability to move forward is dependent on this law. The universe is might infinite, but little things like structures, planets, people and animals are what keeps it going: If you die, the world continues on, you will decompose, became nutrients for plants, herbivores eat those plants, and carnivores eat the herbivores, they die, and life starts over. The Universe always moves forward, a constant cycle. It is the one thing that binds All together... That it is alchemy itself...One is All, All is one.