Quantum Realm

"A reality where all concepts of time and space become irrelevant as you shrink for all eternity."

- Hank Pym

The Quantum Realm is a 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.

Final Mission
"Your mom died a hero. And I spent the next ten years trying to learn all I could about the Quantum Realm."

- Hank Pym 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.

Escaping the Quantum Realm
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.

Rescue of Jemma Simmons
"After hearing about the Pym Technologies disaster, you even thought she'd been reduced to a microscopic level."

- Phil Coulson to Leo Fitz Upon the disappearance of Jemma Simmons through the Monolith, Leo Fitz briefly researched into the Quantum Realm, exploring the possibility that she was there.

Meeting the Ancient One
When Stephen Strange came to Kamar-Taj, the Ancient One sent his consciousness through several dimensions and realities, including the Quantum Realm.

Rescue of Janet van Dyne
To be added

Trapped in the Quantum Realm
Though Janet van Dyne managed to help stabilize Ghost for the time being, they needed more quantum energy to fully heal her. To this end, Scott Lang was sent back into the Quantum Realm with a device to absorb quantum energy. However, while he was doing this task, Thanos used the Infinity Gauntlet to wipe out half the life in existence; Hank, Janet and Hope were among the victims, leaving no-one at the controls to bring him back to the normal world.

Nature and Structure
"You never said how beautiful it was, Scott."

- Hank Pym

The Quantum Realm is said by Hank Pym to be a largely unexplored dimension, about which scientists currently know very little. 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.

Trivia

 * In the comics, the Quantum Realm is known as the Microverse, which consists of many different dimensions all accessible through the same means as they are in the Marvel Cinematic Universe. Notably, the Microverse was also home to the Micronauts, a superhero team. Wasp was also trapped in the Microverse, during the time of her supposed death in Secret Invasion, before being discovered by Hank Pym.
 * Marvel Studios cannot use the name "Microverse" as it is packaged with the Micronauts film rights that are with Paramount Pictures. Dr. Spyridon Michalakis, the film's scientific consultant, coined the new name.
 * The depiction of the Quantum Realm in Ant-Man is based on the former Disneyland attraction.