The Mirror Plane

"We call it a mirror, but that's wrong in a few ways. A mirror reflects back at you the same shapes in the same arrangement. Mirror plane doesn't do that. It's got the same stuff, and as far as our best science can tell, the same amount of stuff. But it's not the same shape. What's an asteroid here could be part of a star there. Water could lead to iron. Iron could go back to nitrogen. And we don't know which one came first. Probably both at the same time."

The Mirror Plane is, in effect, a second universe. Bound to the first by each fundamental particle, the mirror plane is of identical size and mass to the first, but arranged differently. Scientists are unsure why, but theorize that minute differences in the starting conditions of each universe caused the matter in each to settle differently. Thus, particles that can be found on grains of sand at the beach in one universe could be interstellar dust, or the inside of a star on the other end.

Humans have learned to exploit this mirror plane through a mechanism called the Tein Process. By applying current to an isolated particle in hard vacuum, the boundary can be ripped open, transporting an amount of matter from one universe to another. This turns every single particle into a potential link into the second universe, potentially an arbitrary distance away. Unfortunately, most matter in each universe is bound up in a black hole or a star, instantaneously destroying whatever is sent through.

Nevertheless, every once in a while an exploration into the next plane yields a link that can be exploited. Then, both ends of the link are captured, becoming some of the most valuable property in the entire cosmos. Linkages back and forth through the two universes have enabled a degree of interstellar civilization even though no method exists to traverse the interstellar void.

Loopbacks

A loopback occurs whenever matter originating in one plane ends up in the other. Attempting to apply the Tein Process to such particles results in destructive feedback and the energy applied being lost as radiation and heat. Otherwise, loopbacks are harmless, and damage caused by loopbacks is relatively rare. The most common loopback accident results from improper use of mirror knives outside of their intended plane.