The effects of gravity can be explained by other theories. An example would be the acceleration theory which asserts the earth is actually moving 'upward' at a constant rate of 1g (9.8m/sec^2). This produces the same effect as "gravity". note Only that then, everything at the other side of the world would fall to the void.
In one Dilbert strip, Dogbert theorizes that gravity is optional and that this is the reason why most people are stupid: Smart people question everything, and when they start questioning gravity they get flung out into space.
Some tracts go into this territory, claiming that the solar system is held together by Jesus' hand rather than any scientific principle such as gravity (see page illustration).
Others even state that matter is held together on the subatomic level not by gluons, but by the will of God.
In the computer world of The Matrix, gravity is not real because the world is not real. At the end of the first movie, Neo gives the tyrant overlords the proverbial finger by flying off in broad daylight, showing mankind that gravity is not all it's cracked up to be.
You Are Here: If you walk through that door on the seventh floor (the one leading straight out in the air, not to a balcony or bridge or anything), there's only two things to be afraid of as you fall towards the ground... that you will hit it. And that you won't.
Franz Werfel in Star Of The Unborn depicts a far future in which science and theology have been unified by Ursler's Fundamental Paradoxes. The Principle of the Infinitely Mobile Central Point of All Conceivable Orbits has established that the Earth really IS, in some way, the center of the universe, and the official Uranographer moves the stars around every night to spell out the day's news. This actually makes some sense in that statements like "the earth goes around the sun", or vice versa, imply that there is some absolute frame of reference.
The Gospel of the Flying Spaghetti Monster claims that "gravity" is actually the Flying Spaghetti Monster gently pushing us down with his noodly appendages. This theory is supported by the fact that people are taller now than during the stone age, and also more numerous: Clearly there is less gravity for each of us these days, and thus we grow taller.
Invoked by Charles Darwin in an essay 1842: What would the Astronomer say to the doctrine that the planets moved (not) according to the law of gravitation, but from the Creator having willed each separate planet to move in its particular orbit?
In Kurt Vonnegut's novel Slapstick, the protagonist and his sister theorize that gravity was once variable, which is how the Pyramids in Egypt were built. This turns out to be true when their theory is used by the Chinese to change gravity back to how it used to be. From that point on it varies daily.
In The Hitchhiker's Guide to the Galaxy, it was a fairly simple matter to learn how to fly. All one had to do was learn how to throw oneself at the ground... and miss. From a Certain Point of View this is true physically: if you're up at some distance from the surface of the earth and move aside with enough speed, you will be "falling over the horizon". After some time you'll have gone all round the Earth: you're in orbit.
1984: As O'Brien puts it, "I could be floating in front of you right now if I wish it. Right now I do not wish it, because it does not suit the Party."
Live Action TV
Phoebe in Friends states, "Lately I get the feeling that I'm not so much being pulled down as I am being pushed" when Ross compares evolutionary theory with gravity. It was never confirmed whether she was serious or just messing with Ross.
Tim Minchin refers to this phenomenon before playing I Love Jesus.
Tim: “But evolution is only a theory!”, which is true, it is a theory, it’s good that they say that, I think, it gives you hope, doesn’t it, that - that maybe they feel the same way about the theory of gravity… and they might just float the fuck away.
In Mage: The Ascension, Gravity is only one of the many oppressive and arbitrary rules that The Technocracy forces on us and The Traditionswant to get rid of.. On the flip side, because consensus reality sort of becomes the mage's personal reality the closer you get to him, there is often convenient floor-directed 1*g gravity and 1*atm air pressure wherever a mage that's too lazy to come up with better is standing... even if he's standing on an asteroid, in space, with no atmosphere.
Rational Wiki discusses and deconstructs this trope by name in their article on the term "Deepity" (which is a shorthand term for a phrase or statement that sounds vaguely profound but is actually nonsensical). They point out that "Gravity is just a theory" actually is correct... but also point out that many people who use the term are blatantly unaware of the definition of the word, as theory basically means "an idea that everyone agrees upon as correct unless it's refuted by later evidence". So while gravity really is "just a theory" that doesn't mean it doesn't exists and it's stupid to think otherwise. Rational Wiki also encounters a lot of other instances of this trope relating to other subjects. It comes with the territory of their goal of debunking pseudoscience and other such falsities.
In this strip from I Drew This, a preacher is arguing for Intelligent Falling, leading to students walking off cliffs. It is left ambiguous whether they do this because he have convinced them to disbelieve gravity or because his crude discourse has pushed them past the Despair Event Horizon. note This strip predates the Onion article above by a couple of months.
In thisMen In Hats strip, Sam pooh-poohs evolution as "some theory without any evidence," and Gamal tells him that gravity, like evolution, is "just" a theory. Sam's reaction: "Oh I'll float, God damn you."
8-Bit Theater. Fighter attempts to save the group from a lethal fall by blocking the earth. It never occurs to him to factor in gravity or any other forces that might deadify anyone who was stupid enough to try such a thing. It works.
Saturday Morning Breakfast Cerealparodies both Evolution and Gravity "theories". For those less scientifically literate, gravity is actually somewhat poorly understood. While the basic idea of "Two masses exert attractive forces on each other" is sound and verified, the actual theory of gravity is not. Ironically, the understanding of gravity is much closer to the more colloquial definition of theory, rather than the scientific definition. In short, when trying to demonstrate how well grounded the Theory of Evolution is, comparing it the the Theory of Gravity is counter-productive.
Another good example of how the scientific terminology is more nuanced and different than common use: the phenomenon (objects acceleration toward each other in proportion to mass) is firmly observed and existent, the law (that, on the macro-scale, force = g*m1*m2/d^2, and its more thoroughly detailed relativistic version) is well-established and verified as it can get, but the Theory, i.e. the set of explanations describing why these things are so in the context of all the other stuff we know, is not very well fleshed-out.
Pasha: ...you've based this whole report on a theory. Isn't that ad ignorantium? Stephen: I am this close to killing you. That is not what theory means! A scientific theory is something we know is true because of huge amounts of empirical evidence! Gravity is a theory! Atoms are a theory!
In a "U.S. Acres" segment on Garfield and Friends, Roy tricks Wade into thinking that the law of gravity (or "grabbity", as Wade misinterprets it) has been repealed, leading to Wade thinking he's going to fly off into space.
Alan Sokal wonderfully played on this trope, stating: "Anyone who believes that the laws of physics are mere social conventions is invited to try transgressing those conventions from the windows of my apartment." He used to live on the twenty-first floor.
Additionally, there exist several alternative formulations of gravity, such as Modified Newtonian Dynamics (MOND) and Modified Gravity (MOG) which differ from Einsteinian gravity in their asymptotic limit, as a way to account for astrophysical observations without invoking the existence of dark matter.
The force of gravity is also a "fictional" force...the action of Gravity is actually believed to be caused by the bending of space in the presence of matter, and not by an actual force exerted by matter itself.
The exact nature of Gravity - whether it is a Fundamental Force (alongside the affirmed Fundamentals of Strong Force, Weak Force, and Electromagnetism) or whether it is an Emergent Force - is so hotly debated in the scientific community and among enthusiasts that proclaiming support for either stance on a science forum is as close flamebait as one can get in learned circles.
"Only a theorum", other theorums than gravity and evolution
One of the short stories in Vetenskap och Ovetenskap (Science and Unscience) features a member of the Flat Earth Society who dismisses the idea of the Earth being round rather than flat as "only a theory."
SPOCK start their song Alien Attack with dismissing geology as "just a theory". It looks as if they are about to build a case for Earth Is Young, but it quickly turns out that they're actually arguing that the dinosaurs never died out... and now they are back to reclaim their planet!
In Sam & Max: Freelance Police Season 2, Max claims not to believe in the existence of magnetism, insisting it's 'only a theory'. Then he brings out his Luger...only for it to be magnetized to the North Pole. He then says he believes it, "But that's my limit!"
A combination of twostrips plays creationism for laughs by invoking the idea that the theory about the earth moving around the sun rather than vice versa is only a theory. The first strip joke about creationists demanding to put "evolution is only a theory" stickers in biology textbooks. The next strip joke about a guy from the 13th century demanding the same kind of stickers in astronomy textbooks.
In a much later strip, a biology teacher reverses the arguments against evolution— he argues that history is only a theory. More specifically, he does not believe in "the theory of revolution": According to his religion, all states were created in their current form (he handwaves away revolutions he could personally observe as 'microrevolutions' whose resulting states are basically the same). However, he was deliberately using Insane Troll Logic in order to prove his point that teaching Intro Biology was tougher than teaching Intro History, as the latter will (hopefully) NEVER get the kinds of "theories" that the Biology professor would encounter.