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When Dimensions Collide
Two worlds exist and the physical laws or geometries of one bleeds over into the other.

This usually takes one of two forms:

  1. A world with overly simple rules and internal logic entered by somebody from an Earth-like world. These works are more prone to humor as the native inhabitants fail to understand or loudly disbelieve things which would be obvious to normal humans.
  2. A world which has an alien set of physical laws (or somebody from it), that then interacts with an earth-like world. Type II worlds are almost always in the horror genre. Visitors from these worlds are often either The Fair Folk or Eldritch Abominations.

Although this sometimes overlaps with Alien Geometries, it is not about the alien shapes involved (although they can be a side-effect) but rather the idea that something is invading a world by sending their laws of physics first.

The litmus test for being this trope is:
  1. There must be two independent worlds.
  2. Something must cross from one world to the other.
  3. The "laws" of the invading world must work in the invaded world. (for example if a mage comes from magical world A to mundane world B, it only becomes this trope if the mage can cast magic in the mundane world where magic is normally impossible)

Simple worlds invaded by "real world" elements

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  • In Pleasantville, the protagonists are highschool students from our world who enter the world of a 1950s TV serial entirely in black and white, in which everything is excessively pleasant (as well as lacking colour there is no rain, crime, homelessness, fire, sex or toilets). Throughout the film their actions impact the world around them and colours and concepts from the real world (like fire, sex, colour and rain) start to appear as a result.

  • In Flatland, A Square is visited by a sphere from the mysterious dimension of "up" and interacts with the strange world of the third dimension. A sphere manifests as a circle that grows and shrinks, able to bypass all flatlander doors and walls and even touch "inside" a flatlander. The protagonist eventually learns to think multi-dimensionally and is considered insane by most.

  • Erfworld: The world's rules reflect those of a traditional turn-based tabletop game. For example, terrain is divided into hexes and units can only move a certain number of spaces each turn.
    • The protagonist is from Earth. He experiments with the physical laws of the world in an effort to better understand the rules of the game and attempts to cheat with them (even without cheating, mastering the system makes him a tactical genius). He also appears to have several interesting and unique properties that are a hold-over from reality (such as a lack of visible stats, blood, and the ability to get distracted and forget direct orders).

Earth-like worlds invaded by alien elements

    Fan Works 
  • In The Conversion Bureau, Equestria has been transplanted to Earth in the future, not too far off the shore of the USA, by forces unknown. Its magical field is slowly expanding to cover the planet. The field purifies any air, soil, water, plant life, etc within. Unfortunately, the magic is fatal to humans and the expansion is beyond the power of the Princesses to stop. A special potion is devised to transform humans into ponies, changing their bodies while preserving their minds and souls, to let them survive. This is what happens at the eponymous bureaus. In spite of technological advances, Earth is presented as an Earth That Used to Be Better, with deliberate implication by the author that some event between the present day and the fic's time left a lingering effect that causes much of humanity to essentially act smoozed. Ponification undoes this, often causing the transformed to feel very chipper. However, the presentation of all this was not as clear as the author desired, leading to negative Alternate Character Interpretation and Unfortunate Implications.

  • Jumanji: The flora and fauna of Jumanji that invades the "real world" is able to do things that would be impossible for real life equivalents (monkeys that can ride a motorcycle, plants that can grow incredibly quickly, a Pelican that can fly the board game without trouble etc...)
  • Last Action Hero is a quasi-example. On the one hand, when an action hero crosses over from the world of movies into the real world, he nearly dies from a gun shot he'd normally shrug off as Just A Flesh Wound; similarly, a villain who makes the same leap is delighted to discover that in the real world the bad guy winning is actually possible. However, when Death crosses over into reality from the movie world, he's still able to kill people just by touching them. We also see that, when the movie hero shoots the movie villain in his cybernetic eye, it causes a ridiculously huge explosion, even when they're both in the real world. It could be said to be somewhat consistent since only supernatural or futuristic elements kept their original properties.

  • In the Doctor Who Virgin Missing Adventures novel Millenial Rites, our universe gets merged with both the one that preceded it and the one that will follow it, becoming a trifold realm being slowly torn apart by its three mutually-conflicting sets of physical laws. London becomes known as the Great Kingdom, ruled by the gods the Great Intelligence (AKA Yog-Sothoth, of the Pre-Universe), Saraquazel (of the Post-Universe)... and Lady TARDIS (of... guess where). Of note: none of the three planned this, and only the Great Intelligence is at all pleased with the results.
  • The stories of H.P. Lovecraft often involve aliens that dwell in more than the traditional three dimensions and who occasionally interact with Earth. The twisting of logic and geometries involved by interacting with these alien space gods usually drives people mad as they are unable to comprehend them.
  • Isaac Asimov's The Gods Themselves is a story based around a new form of energy that arises when people discover how to exchange matter between parallel universes. The protagonist slowly realises that as they exchange matter between worlds some of the cosmological constants also change very slightly, but with potentially apocalyptic consequences.

    Live Action TV 
  • In Fringe, the space-time continuum is breaking down due to contact between the two universes, which are implied to have slightly different physical laws (the show is inconsistent on that point, though). Interesting as the bleed appears to be two-way.
  • There's an episode of Star Trek: The Next Generation where aliens from another universe with very different physical laws invades the regular Star Trek universe, and start running experiments on the Enterprise crew. Somehow they manage to create some sort of temporary environment where the laws of physics allow inhabitants from both universes to co-exist, but normal parameters within that universe do pretty crazy things to people's body chemistry.

  • In Uzumaki, the inhabitants of a small fairly isolated town begin to notice a repeating spiral pattern that manifests in a number of disturbing ways. People, objects, plants, galaxies, space and time eventually twist into a spiral shape drawing the inhabitants in. The closing scenes show the spiral world below and the narration suggests that this spiral world invades the mundane on a regular basis, leaving only ruins behind when things return to normal.

    Tabletop Games 
  • The Realm of Chaos in both Warhammer and Warhammer 40,000: a mirror universe with physical laws vastly different from our own. Wizards/Psykers can tap the Realm of Chaos for power, but they risk physical mutation and insanity; and if for any reason the boundaries between universes are weakened, the results are always nasty and horrifying in the extreme.
  • In the storyline of Magic: The Gathering, the Phyrexians invaded Dominaria by merging it with an already-conquered plane called Rath. Dominaria was warped to incorporate locations and inhabitants from Rath (including the Phyrexian army), sometimes warping individual creatures or structures into hybrids combining both planes.
  • The Witch Craft supplement "Armagedon" is described as having elements of this in areas that are captured by the enemy, such areas are changed radically into something alien and inhospitable to normal life as we know it. Victims end up fused together in collective masses of flesh and otherwise twisted beyond all recognition.
  • The game TORG is explicitly this trope, in which Earth is invaded by a number of other worlds that each have their own genre-like set of laws (which are spelled out in detail for each area, so in the pre-historic themed North America technology does not work and groups of people devolve into small tribes, whilst in the Pulp themed Middle-East people people drift into stereotypes, their allegiances become easily changeable and good triumphs over evil). The playable characters are those rare individuals who are able to carry their own native laws of physics around with them and exercise them against others.
  • Shadowrun has an element of this when magic (re-)enters the world, changing the limitations of what is possible.
  • Dark Conspiracy. Parts of the U.S. have been taken over by Dark Minions invading through portals from their home dimensions. These areas are known as "Demonground", and they're filled with the corruption flowing from the portals. Common elements include bizarre vegetation and weird organic tunnels.
  • Witch Hunter: The Invisible World. Hellpoints are direct doorways to Hell itself. The areas around them are filled with malign influence and evil creatures. Demons may easily enter the world at these places.

    Video Games 
  • In The Longest Journey, the technological world of Stark and the magical Arcadia are usually well-insulated from each other. However, when the Balance between them begins to falter in the beginning of the game, weird stuff begins to happen in both worlds, such as a TV show about rainforests transporting the viewers into an actual rainforest, or a handheld calculator trapping a mage tampering with it inside.
  • In most of the plot of Wild ARMs 2, the source of conflict was an "encroaching Alternate Universe." The only way to fight this was through a LOT of magic and plot twists that temporarily gave it physical form.

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