Parallel World

In JoJo's Bizarre Adventure, the existence of alternate universes, realities or dimensions is a recurring concept. It is mainly conceptualized as the premise behind certain Stand abilities.

SPOILER WARNING: Part 1-8 spoiler details may follow.

Relevant Stand Abilities

Cream

Vanilla Ice's Stand, Cream is able to devour itself and its user to become a void that devours everything it comes in contact with. Vanilla Ice describes it as a dimension of darkness, though he is unsure himself where exactly the objects are sent to. While in this dimension, Vanilla Ice and his Stand are invulnerable to attacks.

The Hand

Okuyasu Nijimura's The Hand is similar to Cream, able to erase whatever space its right hand touches. Okuyasu states that not even he knows where the voided objects go, but it seems the objects are eliminated like an extremely sharp blade had sliced clean through them. This ability allows the normally short-range Stand extreme distance in its attacks, as it can simply remove the space between itself and a target to bring them within range.

Cube House

In JORGE JOESTAR, the 37th universe's incarnation of Reimi Sugimoto is a Stand with an ability named Cube House. Its interior has a tesseract structure and functions as a time traveling device allowing anyone to travel to different universes and time periods. Its primary usage is to take the person using it to go where someone needs their help the most.

Made in Heaven

Made in Heaven increases the speed or rate of the flow of time; achieved through its ability to control the gravitational forces of the earth, moon, and seemingly the entire universe (in reference to aspects of the theory of relativity).

As time continues to travel, the universe will hit a "vanishing point", and a new universe will be created, where everything repeats itself, according to "fate". Every person in that universe will inherit the memories from the previous one, thus will know exactly what their fate is. Though not being able to change any of that, as everything is already written by fate. This is also the idea of Heaven visioned by Enrico Pucci.

In the story, just after Pucci's death at the hands of Emporio Alniño and the Stand Weather Report, the universe is obligated to restart to its original cycle, as the effects of Made in Heaven are now nullified. In this renewed world, characters of seemingly very similar identities to Jolyne, Ermes, Anasui and Weather Report fortuitously gather in Emporio's proximity. However, the characters now have different names such as Irene and Annakiss, along with different lives and memories. This is a consequence of Pucci's death in the hands of Emporio, as now this world's events happened without Pucci being a part of it.

Dirty Deeds Done Dirt Cheap

President Funny Valentine's Stand, D4C, allows different parallel worlds/dimensions to co-exist at the same time and/or in the same place. It also allows its user to visit these parallel worlds/dimensions and interact with them. Valentine travels by being closed between two objects, shown first by the use of a door against a wall. This method allows practically anything to travel between dimensions, including other people. Valentine takes advantage of this towards the end of Steel Ball Run to bring forth Diego Brando from a Parallel World to aid him. It is noted that anything that comes in touch with any of its alterante universe counterparts, be it an object or a person, both entities will be destroyed. This applies for dead bodies and their alive counterparts, as well. The only exception to this rule is Valentine himself, who can bring other Valentines to this world and interact with them without getting harmed.