All Gravity Is the Same

In Science Fiction settings, characters will often travel to other planets. In real life, gravity is determined by the mass of the object in space — the higher the mass, the higher the force of gravity.^note A planet's radius, and thus density, matters too; for example, Saturn has about the same force of gravity at its surface as the Earth, even with its much larger mass, because its density is so low that the surface is very far from its center of mass. While astronauts will bounce on the moon, they would not be able to jump nearly as high on Jupiter as they can here on Earth.

In fiction, however, gravity does not work that way. All planets will have the same force of gravity, regardless of the planet's mass. Characters will walk, run, and jump around on a planet that has twice the mass of Neptune as easily as they will on planet Earth. This can be justified if the setting establishes that Artificial Gravity is commonplace. It does not apply to spaceships that would need Artificial Gravity regardless. Can be considered an acceptable break from reality, especially for low budget live-action works that can't realistically portray higher or lower gravity.

Baby Planets tend to have the same gravity as Earth-sized worlds.

Note that a planet smaller than Earth could have equal or stronger gravity if it were more dense, but this is unlikely, for several reasons: Earth has the highest density of any known planet, and since it is the largest rocky body in the Solar System, it therefore means that all smaller planets and moons than Earth are also less dense, suggesting that, on average, density may at least partly be a function of size. The elemental abundance of the cosmos and our models of planetary formation suggest that it would be vanishingly unlikely for a planet to be denser than pure iron, which is not even half again as dense as the Earth, unless of course the planet is artificial.

Compare to All Planets Are Earth-Like (where an alien planet has a climate capable of supporting life). Sub-Trope of Artistic License – Space. See also Gravity Sucks.

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Examples:

Advertising

• A 2007 TV Commercial for FedEx is set in a "Moon Office" where the people inside float around in weightlessness, while astronauts outside walk around subject to the expected 1/6-of-earth gravity.

Anime & Manga

• Zig-zagged in Dragon Ball Z:
  • While there are probably more exceptions than straight examples, that doesn't change the fact that it's assumed to be the norm that all planets have a gravitational pull of 1G. For example, Pui Pui believes that by fighting on his home planet with has gravity ten times that of Earth, it will give him an advantage... without realizing that Vegeta's home planet also has 10x Earth's gravity, and in fact Vegeta trains in chambers with hundreds of times Earth's gravity.
  • During the Tournament of Power in Dragonball Super, the Grand Minister justifies the trope by causing the gravity in the arena to affect everyone differently (he's an angel, he can do that), as in everybody feels the same gravity they would on their respective homeworlds. He did this to ensure Heavyworlders would not have an innate advantage.
  • The writers seem to have forgotten that Z established that the planet Vegeta had 10 times Earth's gravity as Dragon Ball GT has Earth's population temporarily moved to a duplicate planet and Dragon Ball Super: Broly has characters with no combat prowess such as, Lemo and Berryblue standing and walking normally.

Comic Books

• Zigzagged with Superman comics. While Krypton's higher gravity is an explanation for a Kryptonian's improved biology compared to humans (even when ignoring the presence of a yellow star), all works that take place on Krypton essentially treat it as just a weird looking Earth.
• Landfall from Saga is orbited by a moon called Wreath and a dwarf planet known as the Robot Kingdom. All three have similarly sized humanoid races that can exist on the same planets and don't seem to be any stronger than eachother. To top it off, Landfall is said to be the largest planet in the galaxy. The largest planet in our solar system is Jupiter with gravity nearly two and a half times our own.

Films — Animated

• There's a mention in WALL•E of the population of the Axiom being weak from microgravity. The robots move at the same speed on both the spaceship and Earth and the humans struggle to walk in either place due to a lifetime on hovering beds.

Films — Live-Action

• Ubiquitous in the Star Wars film series:
  • Mustafar, where the climax of Revenge of the Sith takes place, is six times larger than Starkiller Base from The Force Awakens, and yet characters move as freely on Mustafar as they do on Starkiller Base despite that there should be much higher gravity.
  • In The Empire Strikes Back they're able to walk on an asteroid where in reality the gravity would barely be above zero. Then later they visit Bespin's Cloud City, despite Bespin being a gas giant whose gravity would realistically have crushed them.
  • The expanded universe says that the Forest Moon of Endor has significantly less gravity to explain giant plants and how Ewok hangliders work in Return of the Jedi, though visiting humans seem to walk normally.
• Transformers Film Series
  • Transformers: Dark of the Moon shows Cybertron to dwarf Earth, yet in the flashback prologue all of the robots move no differently than they do on Earth. There is also the problem of the Decepticons teleporting Cybertron directly into Earth's atmosphere, which in real life would be very detrimental to both planets. Defied in all scenes that takes place on Earth's moon, however, where all characters appropriately bounce around in the low-gravity environment.
  • The fifth film, Transformers: The Last Knight, contains the same problems.
• In the novelization to Star Trek Into Darkness McCoy notes the absurdness of the planetoid where they open the missile having earthlike atmosphere and gravity, figuring it must have a very dense core.
• Ego The Living Planet from Guardians of the Galaxy Vol. 2 mentions being the size of Earth's moon but seems to have Earth like gravity. He'd have to be extremely dense at that size to have our gravity and atmosphere but his interior is shown to be full of caverns.
• 2001: A Space Odyssey explains gravity on spaceships by rotating them or having the crew wear velcro shoes but the Moon base seems to have Earth gravity with no explanation.
• Going by the Alien movies, the planet LV-426 seems to have standard gravity but the novelization and screenplay say it has a diameter of 1,200 km. If this was the case, it would visibly be a Baby Planet with a ridiculously dense core to generate any kind of gravity. The Colonial Marines Technical Manual says its gravity is 0.86G and gives it a more realistic diameter of 12,201 km.

Live-Action TV

• In the Power Rangers franchise, most planets have more-or-less the same gravity as Earth. Only one exception has ever been shown, and that was in an episode of Power Rangers in Space, where a planet had such high gravity, the Rangers needed to use their Galaxy Gliders to move about safely.
• Played with in the Star Trek universe. While planets are shown to have similar, if not the same gravity as each other, Artificial Gravity is also very common. One species, the Elaysians, is barely able to function in 'Earth-level gravity' environments without the aid of surgery or special technology due to the low gravity of their home planet.
  • One of the recurring background announcements in Star Trek: The Original Series is "Gravity is down to point eight", which is close enough to standard gravity that everything still looks normal. We never see the Artificial Gravity outright fail, even on an otherwise derelict ship, until Star Trek VI: The Undiscovered Country.
• The Universe Bible for Firefly says their method of Terraforming can increase a planet or moon's gravity, explaining this trope.
• Galactica 1980 has the fleet reach Earth and find that the gravity is a fraction of what their used to, enabling them to leap In a Single Bound. So apparently all the planets and spaceships in Battlestar Galactica have the same gravity a lot higher than Earth's.
• Generally played straight in Red Dwarf even if the world the gang are on is specified to be a moon or an asteroid:
  • An advertisement for the Titan Taj Mahal in "Me2" mentions enjoying Indian cuisine at one fifth Earth's gravity.
  • Notably in "Backwards" Holly realizes they're on Earth All Along because the planet's gravity is exactly 1G.
  • A readout of the condition of Langstrom's Planet in "Quarantine" mentions 1.5G gravity but the guys can walk normally when they get down there.
  • Justified in the Last Human novel that the GELF inhabited asteroids are fitted with Artificial Gravity.

Tabletop Games

• In Space 1889 Mars has .9 gs for some inexplicable reason. Presumably either to explain why it has a breathable atmosphere or to avoid writing up rules for Martian gravity.
• Both averted and played straight in BattleTech, depending on whether or not you're using the core rules (which assume the planet you're fighting on is really close to Earth's gravity) or the optional rules for fighting in heavier or lighter gravity environments, which add a bunch of complications. It's typically justified since humanity in the Battletech universe has generally tried to colonize planets that were as close to Earth in composition as possible.

Video Games

• Astroneer: All planets have the same gravity, at least on the surface, even though they all are different sizes (and Desolo and Novus are moons).
• None of the alternate planets or moons that can be explored in Destiny present any gameplay changes regarding exploration - e.g., the player can jump as high on Earth as they can on Mars without any assistance, players can sprint or slide on every planet as fluidly as on Earth, etcetera. In Real Life, all jetpacks and vehicles would certainly have to be adjusted to accommodate each separate location's different gravitational pull. Somewhat justified on Venus, as it has a similar mass to Earth in Real Life.
• Halo: All the planets and superstructures visited in the series have the same gravity as Earth. A few species like Brutes are said to come from planets with higher gravity but they seemingly have no trouble walking around in Earth-scale gravity.
• In Super Mario Galaxy, the gravity of the various planets, planetoids and other structures in no way effect how Mario (or Luigi if you're playing as him) moves. In the case of artificial platforms and starships like Rosalina's Comet Observatory, it is possible that the Artificial Gravity accomodates to Mario's personal sense of gravity, but the miniature planets (both regular whole ones and the crumbling shells with quantum singularities at their centers) are less justifiable. The scientific implications of this according to Austin on THE SCIENCE are "god damn terrifying!"
• Zig-Zagged in Mass Effect: high-gravity planets are acknowledged in the dialogue, e.g. with the elcor species, which is adapted to the extremely high gravity of their home planet. However, no planet you visit in the original trilogy has a gravity that isn't within the 0.9 to 1.1 range of Earth's (unless Earth's moon Luna and the asteroid from the first game's DLC mission "Bring Down The Sky" qualify), and even those discrepancies have no impact on gameplay or even on animations during cut scenes. Mass Effect: Andromeda does include some real gravitational variation, however — one of the places you visit has gravity low enough to affect your vehicle's handling, enabling jumps you wouldn't be able to pull off elsewhere.

Webcomics

• Justified in Kid Radd: Gravity technically doesn't exist in video games. Rather, many sprites are programmed to fall down if there's nothing below them, and this common trait gives the appearance of gravity as a universal law, but in fact any given sprite will fall at its built-in rate regardless of where it is.

Western Animation

• Despite all the planets visited in Futurama, and the writers usually being very knowledgeable about such things, the only time differences in gravity comes up is in "Brannigan Begin Again" when the crew go to a planet with greater gravity than Earth. Leela warns the crew to use a special hovercart for the delivery, and as soon as they step outside the ship, they are affected by the heavier gravity (Kif instantly slumps to the ground like a stone).
• She-Ra and the Princesses of Power: The planet Etheria has the same gravity as Earth, even though it's absolutely tiny by planet standards. It's possible that the planet's magical energies may have something to do with the source of its gravity.
• Steven Universe: Steven visits three other planets/moon (Homeworld, the jungle moon, and the unnamed planet in "Why So Blue?"), all of which have the same gravity as Earth. However, an exception was made when he went to Earth's Moon, as he bounced around while the Gem's bodies automatically adjusted for the lessened gravity.
• Titan Maximum: When all the planets and moons in the Solar System are terraformed, their gravity is apparently altered to give them all the same gravity as Earth. The main characters are from Titan, but they have no problem walking when they visit Neptune or Mercury.
• Transformers: The planet Cybertron, Depending on the Writer, is either bigger or smaller than Earth. Yet the Autobots' human (and even alien) allies have no trouble with the gravity there.

Real Life

• Any object with the same mass and diameter as Earth would have the same amount of gravitational pull. For example, Venus is the closest object in the Solar System to Earth in terms of mass, so its force of gravity is very similar to Earth's. However, that's the only thing about it that's similar to Earth.

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