Gravity Screw



Subtrope of Gimmick Level. A common level in video games, especially platformers. A trope in which the gravity functions in any way other than "what goes up must come down". More common in modern games than in earlier ones, but there were some in the days of the NES. Usually the change of gravity is local to the player, but sometimes not. Almost always counts as an Interface Screw. More often than not a puzzle level.

Common types include:
 * The Planet: The level is spherical, like a real planet but much smaller, and pulls the player toward its center, which may or may not kill the player if he gets there. Super Mario Galaxy relies on levels like this. Also, a memorable boss in Yoshi's Island.
 * The Unusual Planet: Planets don't have to be round: they can be cubes, pyramids, donuts, question marks, or any kind of crazy shape. Gravity tends to pull in a direction orthogonal to the angle of the ground instead of towards its center; for example walking over the side of a cube planet will instantly flip gravity 90 degrees towards the next face (instead of the character seeming to walk over the crest of a mountain, it's more like walking over a cliff).
 * The Inverse Planet: The level is round, but in the other way - a hollowed-out space that pulls the player toward its walls. Mission 03 in Strider 2 featured a boss battle in a chamber like this.
 * Cross Gravity: Gravity pulls in a particular direction that's not down (as seen by the viewer) - maybe to the left.
 * Upside-Down World: Gravity pulls upwards. Aforementioned Strider 2 level also featured one of these.
 * The Rotating Castle: The entire level rotates, but the player stays in place. Gravity continues to pull down, but it has a similar spirit to the Upside-Down World mentioned above. Super Castlevania 4 has a brief room that functions like this.
 * Toroidial Gravity: Gravity wraps around the outside of a cylinder; objects that start falling without running into something will just circle the object indefinitely. Super Mario Galaxy 2 has some of this.
 * The Variable Gravity Chamber: Gravity changes based on your physical location in the room. The direction of gravity's pull is usually indicated in the background, or there are specific devices that change the direction of gravity. Many of the Bowser's Castle levels in Super Mario Galaxy featured areas like this.
 * Fun With Gravity: Gravity changes at fixed intervals. At best, a severe Interface Screw. At worst, timing will be essential to prevent you from flying into a Bottomless Pit (or Ceilingless Sky), in which case expect this level to be Nintendo Hard as all get out.
 * Heavy Zone/Light Zone: Gravity is either much greater or much less than usual.

Anime & Manga

 * Dragonball Z used the "spherical planet" variation; when Goku reaches the end of the Serpent Road, he looks around and sees something floating in the sky above him, so he jumps towards it. To his surprise, he starts falling towards it.
 * Also the gravity machines the Saiyans use for training later in the series, except those were intentional. And instead of "what goes up must come down" being the norm, it's "what goes down stays down, and everything goes down. No exceptions." Heavy Zone doesn't even begin to describe it—Vegeta claims to have trained (off-screen) at over 400 Gs, and Goku trains at both 10 and 100 (and several levels in between) on-screen.

Art

 * Artist M. C. Escher's Relativity.
 * That has been the subject of many Shout Outs, some of which are noted above.

Film

 * The freaky room at the end of Labyrinth where down is wherever your feet are. Jareth is right at home here - the heroine, not so much.
 * Inception has several scenes in the dreamworld where gravity simply doesn't exist, and a very reasonable explanation for it: changes in real-world gravity carry over into the dream, and
 * In one scene, the characters in one dream level are in a van rolling over, and due to dream time-dilation, seconds turn into minutes in the next dream level down (and even longer in deeper dream levels). Cue revolving corridor fight scene.
 * To those of us familiar enough with physics (or at least with centripetal forces and noninertial reference frames) this particular scene is big-time Fridge Brilliance.
 * When the vehicle in the 1st level of the dream makes sharp turns, . This makes sense because a sharp turn involves centripetal acceleration, and in turn could make it feel like the angle of gravity is changing.
 * When the vehicle in the 1st level of the dream is This makes sense because the acceleration of the vehicle is "almost" equal to that of gravity (in practice held back by friction, but let's grant them slight inaccuracy in sci-fi) thus to the passengers, it would feel like they are weightless in the noninertial reference frame of the car, hence they would be dreaming of weightlessness.
 * Despicable Me features an anti-gravity serum.
 * In Ultraviolet, Violet wears a gravity leveller on her belt that allows her to use this trope to great effect. Her motorcycle has such a device as well, allowing her to flee from her foes along the sides of skyscrapers.
 * In Tron: Legacy, the Disk Wars area in which Rinzler fights has this feature. Since Rinzler is aware of this, he's able to land gracefully on his feet, unlike poor Sam, whose landings are a bit rougher.
 * Fred Astaire's famous rotating room/"Ceiling Dance" routine from Royal Wedding.

Literature

 * Robert Heinlein's Glory Road. While exploring the Tower in Karth-Hokesh, Oscar Gordon and his team encounter areas where the gravity reverses itself and the ceiling becomes the floor.
 * The mist in the maze in Harry Potter acts as a local inverse-gravity zone to anyone who steps into it. After a few seconds of feeling like he's about to fall into the sky, Harry works up the nerve to take his feet off the "ground", at which point he snaps back to reality.

Television

 * Stargate SG-1:
 * In the season 6 episode titled "Abyss", the System Lord Ba'al is shown to be experimenting with gravity. Ba'als fortress has prison cells which at first appear to be long hallways, however, once a prisoner is added to said cell, Ba'al turns on some artificial gravity in the cell and the far wall becomes the new floor. Any prisoner within said cell then sees their cell as a 50 foot tall pit with sheer walls and no doors. The only way to escape said cell to power down the entire fortress thus turning off the artificial gravity.
 * As opposed a simple 50-foot-tall pit, which would work even if the power went off

Tabletop RPG

 * Dungeons & Dragons:
 * In Planescape cosmology some planes (in the original Manual of the Planes (1987), on the Elemental Plane of Air, later on others as well) have "subjective gravity". There's no intrinsic "up" and "down", so inanimate objects are halted at least by air friction, but thinking travellers may choose the "down" direction and automatically move in that direction. (Provided that they knew that the laws of physics didn't apply in the Plane of Air... otherwise, they'd assume that "down" was whichever direction their feet were facing, and fall infinitely. Not that it would kill them, of course: Air is not so empty that it's possible to collide with something else, but this happens very rarely. On other planes it may happens e.g. in tunnels. In which case several nearby creatures tend to "settle" on a single direction.
 * The above extends all the way to 3.5. In the fourth edition, they have some different Gravity Screws. On some planes gravity is subjective, so you can walk across any surface including walls and ceilings. Also, you can simply choose not to be affected and effectively fly with poor maneuverability.
 * The Reverse Gravity wizard spell.
 * A Polish tabletop RPG, Strefa Smierci ("Death Zone"), featured gravity anomalies as one of the dangers of the wastelands; an anomaly would appear as an aftereffect of the area getting bombed with high-level phlebotinum. Unexpectedly walking into one was one of the easiest ways to die there.
 * GURPS has rules for operating in high or low gravity. Zero gravity can result in the character becoming physically ill.

Video Games
"As far as the laws of mathematics refer to reality, they are not certain. As far as they are certain, they do not refer to reality."
 * Very common in the Sonic the Hedgehog games.
 * Sonic 3s Carnival Night, Sonic 1s Scrap Brain Zone, and Sonic CD's Metallic Madness Zone all feature wheels that function as miniature planetoids. Death Egg Zone from Sonic And Knuckles involved spinning antigravity passages and a sideways gravity chamber in Act 1, then Act 2 involved gravity frequently switching upside down and back--and one of the bosses could only be defeated by manipulating this mechanic. Sonic Adventure 2 and Shadow the Hedgehog feature Crazy Gadget and Space Gadget respectively, both defining examples of gravity that can go in any of a number of directions.
 * The Mad Space level is more like most of Super Mario Galaxy, with the direction of gravity being dependent on which planetoid you're closest to. There are also drums in Final Chase that pull you onto their surface when close enough.
 * And Cosmic Wall, also from SA2, was a Light Zone.
 * For another Sonic example, the Cyber Track Zone in Sonic Advance 3 has areas within all three Acts where gravity reverses automatically.
 * As well as Cosmic Angel in Sonic Advance, Egg Utopia in Sonic Advance 2, and Dead Line in Sonic Rush Series.
 * The entire point of Sonic Riders: Zero Gravity.
 * Most of the time, the gravity switching does little else but look damn cool. Running on the ceiling above a floor full of spikes? Hell yes.
 * Asteroid Coaster Zone in Sonic Colors.
 * One of the Yoshi's Island games had an area where you had to switch repeatedly between the right-side-up area and the upside-down area to avoid dangers.
 * Another Yoshi game, Yoshi Topsy-Turvy, had a tilt sensor inside the cartridge, allowing the player to control gravity at will. It only allowed for angling sideways, however.
 * Another Super Mario Galaxy example, of the Fun with Gravity variety, is probably the second mission of the Dreadnought Galaxy, which has platforms going normal way up, upside down and sideways at various points along a route where Mario is being fired at by various cannons. Definitely falls under the Nintendo Hard bit. And similar kinds of puzzles in Bowser's Dark Matter Plant.
 * The internet flash game Shift does this.
 * The Distortion World in Pokémon Platinum has you walking on the walls at times, and it kind of messes up the control system a little right after you get back.
 * The anime's equivalent from Giratina and the Sky Warrior, the Reverse World, is even worse with how gravity works. One scene involves Team Rocket all standing at three completely different angles while close enough to reach out and touch each other.
 * Stone Temple Tower in The Legend of Zelda: Majora's Mask has you switching between normal and flipped.
 * Ocarina of Time's Forest Temple could be seen either as an example of this trope or a subversion. There are switches you hit to twist or untwist a long hallway, so you could end up entering the room at the other end either walking on the floor or on one of the walls, but the camera always turns to keep Link seemingly on the ground, while everything else is moved.
 * Although it wasn't even interactive, there's a twisted tunnel at the beginning of Majora's Mask - the player walks along the "floor", but it twists around the room (which the player automatically walks through).
 * The Goron Mines in Twilight Princess don't involve playing with gravity per se, but some of the rooms have magnetic walls/ceilings that Link can walk on with his Iron Boots.
 * Similarly, any area in which you had to use the Magnetic Gloves to get across pits in Oracle Of Seasons.
 * Shatterhand had a level like this.
 * In Jedi Outcast there is a brief zero gravity section aboard the Doombringer
 * VVVVVV's entire premise is based on this, and is modified by many, many obstacles.
 * Legend of Dragoon: "The Valley of Corrupted Gravity".
 * The main point of the flash game Mind Scape.
 * And Yet It Moves is a recent example where Gravity Screw is actually one of the fundamental game mechanics.
 * The Freeware Game Jumpman also lets the player rotate the room at will.
 * Mega Man 5 had Gravity Man's level (variable gravity) and Star Man's level (low gravity).
 * V in the Game Boy series has Saturn's level, with examples of high and low gravity.
 * Cyber Peacock's level in Mega Man X 4 had buttons that flipped the stage (gravity still pointed downwards) every so often.
 * Gravity Antonion's stage in X8. Dark Dizzy's level in X5 has a similar gimmick.
 * In the final area of Mega Man Legends 2, there are consoles that let you set gravity to low, normal, and high, allowing you to access different areas based on the current gravity (such as jumping on a weak floor in high gravity to break it). You're also forced to high gravity immediately whenever you touch security lasers in the area, making you take detours when you need to keep low gravity.
 * The PC game Rosenkreuzstilette had a level late in the game that worked just like Gravity Man's level, with flipping gravity. Given that the game was a tribute to Mega Man and Castlevania games, it's no surprise, really.
 * Lost Vikings featured anti gravity zones which sometimes would have to be passed using Gravity Boots because of ceiling spikes.
 * Kingdom Hearts had something similar, in that the characters walked on the floor, walls, and ceiling of the first room of Wonderland at different points. The difference is that they never jumped from wall to floor and so forth; they had to go around to use doors and such.
 * Sure, that could fall under the "hit a switch" variety.
 * Kael'thas Sunstrider in World of Warcraft turns the gravity off completely, leaving players "swimming" in the air.
 * Which brings us to yet another Sonic example, as this also happened near the end of the battle with the Biolizard in Sonic Adventure 2.
 * Some levels in Psychonauts, such as Sasha's Shooting Gallery which takes place on the outside of a cube, and The Milkman Conspiracy, a literally twisted suburb with streets curving every direction.
 * Lungfishopolis from the same game is also an example of a Heavy Zone—your jumps are slower, your Ground Pound is different, and you can't levitate due to your weight.
 * Metroid Fusion has Nightmare, who combines Fun With Gravity and Heavy Zone by making it so you can barely jump and you can't use missiles (they arc straight into the ground).
 * Metroid: Other M uses a similar mechanic in the rooms leading up to
 * Platformer Vexx has an Upside-Down World puzzle in one chamber, where the entire screen flips upside down along with the world.
 * Luigi's Mansion has a few switches in various rooms that reverse gravity. They always come in pairs, because the doors are too low to the ground to exit without being on the floor.
 * The Whoa Zone of Super Paper Mario has the "hit a switch" variety. Sometimes even passing through a door could do it, depending on the doors' relative orientations.
 * In addition, the Tiny Planet (Chapter 4-2) was a Light Zone.
 * Paper Mario: The Thousand-Year Door had the moon as a Light Zone, with good reason.
 * Fairly common in Prey, both with switches that changed gravity, and wallwalks, which were walkways that often turned upside down, allow people on it to defy gravity.
 * In Elastomania, collecting apples can change the direction of gravity.
 * One obscure NES game, Metal Storm, let the player do this pretty much at will. Some later levels required you to flip gravity multiple times in the middle of jumps to clear obstacles without falling into a Bottomless Pit on either end of the screen.
 * Do not forget the boss battle where both the floor and the ceiling (or vice versa, as the case would be) are harmful, and the only places where you can stand are the very bosses you are destroying.
 * Part of The Very Definitely Final Dungeon in Tales of the Abyss is like this, of the rotating room variety.
 * The level of gravity on the various planets in Meteos runs the gamut, but the most notable is Gravitas. The gravity is so high that blocks hit the ground instantly and don't rise at all when they're first matched.
 * Hevendor is the exact opposite. All pieces launched are completely and instantaneously removed from play.
 * Odd example with the c64 game Ancipital which should fit the trope but isn't in any of the categories already described - Gravity changed depending on if you were standing on the floor, ceiling or walls, jumping flipped gravity 180 unless you decided to land on a wall. I suppose it could be described as a variant of the Variable Gravity chamber...
 * Ratchet in the Ratchet and Clank get gets gravity boots from the second game forward. When on a corresponding gravity surface Ratchet and his weapons have their own personal gravity.
 * One game was going to have gravity spheres with a similar effect, but they were deemed too confusing.
 * Dead Space had a lot of sections like this. There were anti-gravity chambers inside the ship, and external sections where if you jumped wrong you'd just float off into space.
 * Don't forget the chambers where the gravity plates have gone haywire; if you see a faint pillar of translucent energy crackling up from the ground, do not walk into it! The distorted gravity will rip you apart in an instant. On the plus side, Necromorphs also get torn into pieces if they enter these spaces, either deliberately (though the AI is generally good enough that they'll go around them, they will charge right into them if you're lucky) or by being knocked into them.
 * The Brinstar Depths level in Super Smash Bros. Melee rotated. However, gravity continued to pull in the same direction, so if you didn't jump just before it happened, you'd get pulled off of the level.
 * And Battlefield of the same game features floaty gravity, but only when fighting wireframes..
 * The Magic School Bus Explores The Solar System computer game features Heavy Zone/Light Zone gravity for the planet-based platforming levels in the game. Planets with less gravity, like Mercury and Pluto, would allow you to jump really high, while planets with a lot of gravity, like Jupiter (or rather, its moon Io) and Saturn('s rings) would make it so you could barely jump at all. (There were also items that would increase or decrease your jumping ability.)
 * The "gravity remains down, but everything else is screwed up" version is seen in the Very Definitely Final Dungeon of Dawn of Mana.
 * "Hero Klungo Sssavesss Teh Universsse", a Game Within a Game from Banjo-Kazooie: Nuts & Bolts (in the downloadable content) has arrows that change your personal gravity.
 * In Kid Chameleon, when in the SkyCutter form, gravity was in the direction your Hover Board faced: Either up or down.
 * A third of the levels in Elebits have no gravity, and any user-made level can have weakened gravity.
 * The free Space Cadet 3-D Pinball game that comes with many Windows computers has an unlockable effect where a gravity well appears in the middle of the board, attracting pinballs towards it until one is sucked into the center, at which time gravity is normalized again.
 * The first secret level in Quake had about a fifth of the usual gravity.
 * Ditto for the secret Satellite level in Quake II.
 * The fourth hole in Fuzzy's World Of Miniature Space Golf was called "Goofball Gravity", in which the ball rolls uphill.
 * The original Thrust had reverse gravity equivalents of all the levels once you got past the normal gravity versions.
 * World of Goo features a Planet-type level and a Rotating Castle-type level.
 * In Serious Sam: The First Encounter the level "Sacred Yards" contains an area where some places have reverse gravity. Very trippy, especially when quickly moving from one area to the other and back.
 * The Second Encounter, has a level with some confusing mechanics, including a room inside a cylinder (with gravity directed towards the walls) and several areas with low gravity. How do you like a tiny room where everything constantly bounces up and down at warp-speed, including the hordes of enemies?
 * Crystal Caves has a couple of levels with "low gravity" (although it manifests just as your character being shoved back when he shoots), and there are also levels with reversed gravity. The game also features a reverse-gravity powerup in some levels and a cheat code that lets you reverse the gravity whenever you want.
 * Several levels in Unreal Tournament have low gravity, either everywhere in the level or just in certain areas. The game also comes with a mutator you can use to force low gravity when playing, regardless of what the map specifies.
 * It is possible to design levels with rooms having reverse gravity or the ability to walk up on the walls. In fact, there is a map trigger that can be used to induce a zero gravity environment where the player can move as if underwater.
 * Cave Story had a strange variant of this in the Outer Wall area, where the player fell normally, but enemies and powerups fell sideways—even the powerups that weren't normally affected by gravity.
 * It might be that the island was moving and you were on the outside wall on the "front" of it. Therefore, The island was moving into the powerups faster than the items could fall "downwards".
 * Armed and Dangerous features a literal Gravity Screw: The Topsy Turvy bomb, a weapon that consists of a giant screw with a handlebar that screws itself into the ground. It then briefly turns the entire world upside down, causing enemies nearby to fall into the sky (you don't, because you've got this handy giant screw to hold on to)... And then, shortly after, fall back to the ground with messy results.
 * Later on in System Shock 2, you make it into the UNN Rickenbacker, where the artificial gravity has flipped upside down. Fighting cyborg assassins in an inverted chapel is a rather creepy experience...
 * Not to mention that by reversing the gravity, you have most likely caused the death of a certain character by dropping him unexpectedly on the ceiling.
 * The upper floors of Constantine's mansion in the Thief mission "The Sword" feature Gravity Screw effects, among other weirdness.
 * Dynamite Headdy had Vice Versa, a level where the player could turn the level upside-down using switches. The miniboss here had to be beaten by dropping balls on it. Right after that was Twin Freaks, where the look and attitude of the boss changed depending on whether gravity was reversed.
 * In Rad Gravity, the planet Turvia has reversed gravity.
 * The web game Swindler by Nitrome is based around being able to rotate the rooms.
 * But That Was Yesterday has some minor gravity screwing of the "rotating castle" varity when the player uses a swing.
 * In Solar Jetman, each planet has a different level of gravity - the higher the number, the more the jetpod will be attracted to the surface. And yes, one planet does have negative gravity.
 * Super Mario Land 2 had the Space Zone, two levels of platforming in low gravity. The floaty jumping combined with a maze of dangerous stars helped to turn the second stage into That One Level.
 * In Dystopia, Cyberspace uses a combination of "variable" and "light zone" gravity. In nodes, touching certain surfaces changes the direction of gravity. In tubes, there is no gravity, but up and down change depending on where you are.
 * The circus-themed levels in Castlevania: Portrait of Ruin do this with round levels where the stage's gravity points a certain direction relative to the landscape (outward first, then inward), while your characters' gravity is constantly downward. It's certainly a surprise when you defeat Medusa and realize she's been fighting upside-down the whole time.
 * Symphony of the Night also has the Inverted Castle, which is Exactly What It Says on the Tin: a vertically flipped version of the normal Castle.
 * The main way you can move Locorocos left and right in Loco Roco is based on that.
 * Super Mario Galaxy 2 has Flipsville, in which you flip grates to reverse gravity. Where gravity's pointing is denoted by arrows in the sky.
 * There's also Upside Dizzy. Not only are there segments of this mansion (?) that have gravity point towards the ceiling, gravity flips in several parts of the level on its own.
 * In the Flash game Epsilon, you control a ball and a pair of wormholes collecting orbs to power the exit. Eventually, you encounter devices that cause gravity to point in a different direction or turn it off entirely. On level 5g, this message appears;


 * ...and all of a sudden, the laws of gravity get bent so hard it's a wonder they don't just fall apart. Not only have the event horizons of the wormholes grown, wormholes now alter gravity entirely. You could be pointing down before going in one wormhole, and left after you come out the next. And it also can be changed by the direction you enter them!
 * Mass Effect 1: . Witness Shepherd and his team stepping out of the elevator and onto the wall, as the camera rotates to change perspectives. Killed enemies will proceed to fall towards what would normally be down.
 * Heretic Station in Mass Effect 2 lacks any gravity; however, the player and their squadmates remain grounded by using special equipment. Thus, the lack of gravity doesn't affect gameplay...but enemies float away amusingly when you kill them.
 * In one level in Modern Warfare 3, you play as one of the bodyguards of the russian president as his plane gets hijacked by terrorists. While fighting your way through the traitors, the plane enters freefall for a few seconds during which you have to fight in weightlessness until someone gets the plane back under control.
 * Mc Donaldland (or Mc Kids depending on locale) has some platforms with cogs on the ends which, if run across, will flip you onto the other side of the platform, reversing gravity in the process.
 * In Stunt Copter, where you repeatedly send a man plummeting from your copter into a horse-drawn haywagon, gravity varies between levels. A helpful readout informs you of the Earth's current mass, eg. NORMAL, HEAVY, or OH BOY.
 * The fourth stage in the original Gradius is an inverted version of the first stage, complete with reverse-gravity erupting volcanoes.
 * The Ur Example of Gravity Screw in video games is located in Space War! where the ships and missiles can optionally gravitate towards the center of the level.
 * The Star Control games use the same setup, with each battle being two ships dueling in space around a planet.
 * The SNES game Mohawk & Headphone Jack uses the Inverse Planet variation, but in an unusual case for the 16-bit era, makes full use of the system's rotational capabilities so that the floor is always facing down. And yes, the entire game is like this, not just one level. The result can, needless to say, be very disorienting at times. You can see it in action here.
 * In Tales of Monkey Island Chapter 4: The Trial and Execution of Guybrush Threepwood, one of the buttons on De Singe's Auto-Trepanation Helmet turns the whole room in the lab upside down along with Guybrush for a few seconds.
 * A level in Kirby'sEpic Yarn has gravity switches that can turn the gravity on or off.
 * In the final parts of Limbo there are switches that at first invert gravity for some select objects, later they affect everything including you; and near the end gravity starts changing periodically.
 * De Blob 2 involves gravity plates, allowing Blob to climb up certain walls.
 * The interior of the alien ship in Crysis has no gravity whatsoever, despite being buried under a mountain. The switch is not sprung on you in a hectic situation, and so you have a fair amount of time to get the hang of moving in zero G before encountering enemies. Thankfully, your suit has some sort of maneuvering system that means you aren't particularly hindered by this. It's actually rather fun once you get the hang of it.
 * Unreal 2 has a ships artificial gravity play up, first allowing to jump large distances, then pulling you against different surfaces.
 * One of the levels of the classic arcade game Marble Madness is the Silly Stage, where you must guide the marble from the bottom of the course to the top, rolling it uphill with the same ease the marble would normally roll downhill.

Web Animation

 * The CCC series has a rewind-style episode where gravity is altered for someone thanks to a drug. On a sobering note, if you find and watch the forward version, this trope is played realistically

Webcomics

 * In Schlock Mercenary, gravity is a weapon, and gets used in all sorts of perspective-bending ways. One arc even involved a group of parkouring vandals who used the weird nullified gravity in the middle of an old space station to run amok throughout the station.

Web Original

 * Up yours, gravity!
 * Turn gravity back on!!!! QUICK!
 * Dead Fantasy Part II features a running/falling battle down the side of a miles-high stone tower. And it is awesome.
 * Upside down ice fishing

Western Animation

 * Futurama featured a parody of M.C. Escher's famed painting.
 * So did the theme song to the animated version of The Addams Family.
 * What is the quickest way to abort a baby in Drawn Together? The M. C. Escher-Room!
 * The Simpsons used the M. C. Escher Relativity joke twice. Once for a Couch Gag and in the movie when Homer fell down all of the stairs.

Real Life

 * Outer space. The moon in particular is a well-known Light Zone.