The Quantum Realm is an alternate dimension only accessible through magical energy, mystical transportation using a Sling Ring, or by tremendous subatomic shrinking caused by the Pym Particles. In the Quantum Realm, space and time are believed to be irrelevant.
Access to the Quantum Realm was finally realized by scientist Doctor Hank Pym through the use of Pym Particles, particles of an extra-dimensional nature that are capable of altering the size of beings or objects. Janet van Dyne, Pym's wife and the first person to bear the mantle of Wasp, disappeared into the Quantum Realm after sacrificing her life to disable a Soviet nuclear missile. Janet van Dyne became a resident of the quantum realm through this sacrifice. Following this event, Pym dedicated himself to researching the Quantum Realm, though he was unable to generate concrete results or information.
After his battle with Darren Cross, Scott Lang was briefly left trapped in the Quantum Realm, but managed to escape by altering the Ant-Man Suit's mechanisms; replacing the shrinking regulator with an enlarging one by installing a blue Pym Particles Disk in his regulator. Lang claimed to have no recollection of what he experienced there however, much to Pym's disappointment.
Upon the disappearance of Jemma Simmons through the Monolith, Leo Fitz briefly researched into the Quantum Realm, exploring the possibility that she was there. When Stephen Strange came to Kamar-Taj, the Ancient One sent him through several dimensions and realities, including the Quantum Realm.
Nature and Structure
The Quantum Realm is said by Pym to be a largely unexplored dimension, about which scientists currently know very little. Hank Pym also says the concepts of time and space become irrelevant when entering the realm, and whoever tries to explore it may become trapped "for eternity."
Scott Lang's incursion into the Quantum Realm began on a microscopic level, then entered atomic size, later dissolving into pure energy and waves, then in a fractal-like reality where the shrinking person meets an infinite number of mirror images of themselves (a possible indication of the "soul" concept), and ending in a weightless dark void with pockets of dim light.
The Quantum Realm is one of many universes in the Multiverse.
