This article is about a non-canonical topic in the Metal Gear series.

The Koppelthorn Engine is a quantum calculations system. When connected to virtual reality devices it allows the construction of simulated environments containing a hitherto unprecedented amount of information. That information is converted into a signal and conveyed into a person's brain via a headset, directly synthesizing information for each of the senses while simultaneously cutting off feedback from the body. That way, it's possible to realize a VR environment that is completely indistinguishable from the real world, down to the lights, sounds, even the sense of smell and touch. There are side effects to using this device, such as the feeling of possessing someone else's body, and vice-versa. That's because of the pseudo-signal filling the brain. Theoretically, it should be possible to replicate exactly the same stimulus as from the sensory structures of a physical body.

How it is able to function is a mystery. It is shaped like a black box, with the insides only holding some kind of circuitry, gears, and iron-like spheres. Pseudo-scientists have only been able to come up with theories that it is powered by technology from extraterrestrial beings or a long lost civilization.

The Koppelthorn Engine doesn't simply create virtual reality tests, but can actually manage to get around barriers that separate parallel universes that satisfy certain requirements, and incorporating that data into the VR systems scenario constructor. Peering and interfering with another universe can cause some disturbances, making it so universes start to combine with each other and warp space and time itself.

Sometimes, a "singularity" can break into another universe, and the only way to restore each universe would be to capture the singularity and perform a counter-unitary conversion via the Koppelthorn Engine, thereby dispersing the wave function to its state before convergence.

Dr. Koppelthorn is the creator of this device. It was designed as part of a grid computing system spread between all the parallel universes. Grid computing is a technique for creating a networked supercomputer with massive computational abilities by connecting numerous servers. Having such a system working on a multi-universal level would yield near-limitless computing power.

Otacon invented a new VR headset, which he connected with a Koppelthorn Engine. Once it was coupled with the headset, a powerful device on it's own, it unintentionally became possible to control possibility itself. When a VR system using the Koppelthorn Engine is instructed to build a virtual reality having a given set of conditions, it selects a group of universes having the potential to satisfy those conditions from among a still indefinite number of parallel universe that still have wave functions that have not converged. It then presents these as a VR construct. What is actually a VR training in the headset is nothing less than the external observation of, and interference with, that group of parallel universes. When one goes through VR training, the actions within virtual reality are reflected in a set of corresponding universes. The resulting interference simultaneously acts as observation with regards to a group of still indefinite parallel universes beside the one that is receiving the interference. That means that the possibilities of the universe converge on the conditions corresponding to the action that person took. For example, let's say a soldier has just killed an enemy within the VR simulation. That means that the universe containing the killed enemy was observed and made definite. In other words, universes where that enemy soldier had not been killed lose their indefinite potential and are erased from all existence. The only universe permitted to exist in the end is the one that doesn't contradict the action taken in the VR simulation. Whenever a mission ends in failure, or the option is picked to try again, the potential for existence for that very universe is denied and eliminated as never having existed. Every time any mission is replayed, an uncountable number of universes are destroyed. In simpler terms, it's a Time Paradox on a multi-universal scale. It is possible to also be observed by other universes. If someone in, say, Universe A, were to observe someone in Universe B, B would feel like their body was no longer their own. B in this instance might be able to do something outside of their experience, something impossible and not thought of before hand. This could be the reason why some people have issues of detachment and a diminished sense of reality.

When the Koppelthorn Engine appeared to malfunction, this resulted in the appearance of the giant monster Gurlugon, as well as an alternate version of Olga Gurlukovich who aided Solid Snake. Solidus Snake (or rather, an alternate version of him) was later revealed to be behind the malfunction, as an act of self-preservation. Defeating Solidus seemingly fixed the problem, although the reports of Genola sightings implied that this might not be the case.