Irresistible force paradox

The Irresistible force paradox, also the unstoppable force paradox, is a classic paradox formulated as follows:

What happens when an irresistible force meets an immovable object?

Common responses to this paradox resort to logic and semantics.

• Logic: if such a thing as an irresistible force exists, then no object is immovable, and vice versa. It is logically impossible to have these two entities (a force that cannot be resisted and an object that cannot be moved by any force) in the same universe.

• Semantics: if there is such a thing as an irresistible force, then the phrase immovable object is meaningless in that context, and vice versa, and the issue amounts to the same thing as, for example, asking for a triangle that has four sides.

A third response to this paradox employs the humor of exaggeration: "The result would be an indescribable collision!"

This paradox is a form of the omnipotence paradox, but that paradox is most often discussed in the context of God's omnipotence (Can God create a stone so heavy it cannot be lifted, not even by God Himself?").

The paradox should be understood as an exercise in logic, not as the postulation of a possible reality. According to modern scientific understanding, there are no immovable objects and cannot be any, and no force is completely irresistible, as even a minuscule force will cause a slight acceleration on an object of any mass. An immovable object would have to have infinite inertia, and therefore infinite mass. Such an object would collapse under its own gravity and create a singularity.

An example of this paradox in non-western thought can be found in the origin of the Chinese word for paradox (Chinese: 矛盾; pinyin: máodùn; lit. 'Spear-Shield'). This term originates from a story (see the Kanbun example) in the 3rd century BC philosophical book Han Feizi.. In the story, a man was trying to sell a spear and a shield. When asked how good his spear was, he said that his spear could pierce any shield. Then, when asked how good his shield was, he said that it could defend from all spear attacks. Then one person asked him what would happen if he were to take his spear to strike his shield; the seller could not answer. This led to the idiom of "zìxīang máodùn" (自相矛盾), or "self-contradictory."

In Popular Culture

• In issue three of the comic All Star Superman by Grant Morrison and Frank Quitely, Superman is posed the question "What happens when the unstoppable force meets the immovable object?" He replies that "they surrender." This question also arises when comic fans wonder who would win between Marvel's Juggernaut and The Blob: Juggernaut would win unless the duel happened on an adamantium planet.

• The popular Blizzard Entertainment video game World of Warcraft makes reference to this paradox in the form of two in-game items: The Unstoppable Force is a two-handed mace, whereas The Immovable Object is a shield, prompting the question, "what would happen if the Unstoppable Force were to hit the Immovable Object?" When this question was posed to one of the designers, he answered with "Chuck Norris dies," another pop culture reference often used in World of Warcraft.
  • In comedic parallel, World of Warcraft also features an item called The Stoppable Force.

• During the broadcast of WrestleMania III in 1987, commentator Gorilla Monsoon associates the paradox with the matchup of Andre the Giant and Hulk Hogan, in what would eventually become one of the most famous moments (and quotes) in professional wrestling history.

• The voice of John Madden uses the line in the Madden video games as commentary during the action.

• The author Iain Banks uses the paradox in his book Walking on Glass

• The Suikoden Series features this paradox as its creation myth, "In the beginning there was darkness, then the darkness shed a tear, the tear became a sword and a shield, The shield claimed it could defend against any attack, the sword claimed it could pierce any defense, they began a legendary battle, at the end both sword and shield shattered, the sword became the sky and the shield became the earth, the sparks from their battle became the stars.."

• In the 2008 film "The Dark Knight," the Joker refers to his struggle with Batman as an unstoppable force meeting an immovable object.

• The 1982 "Knight Rider" episode, "Trust Doesn't Rust" uses this paradox in an attempt to conclude the outcome of a battle between K.I.T.T. and his equally-powerful twin, K.A.R.R.

Alternative Views

1. An immovable object must be anchored within the zone of physical reality so, if an irresistible force meets it, the object will not move within its relative reality, but the entire reality itself may move.

2. The force will pass through the object, and the object will not move. Who is to say that one or the other is solid, or even made out of materials that can interact with each other?

3. If these two forces actually existed in reality and were to collide it would cause what could be called "infinite potential". Meaning by colliding these two omnipotent forces anything is possible due to the fact that they represent ultimate power.

4. The two will cancel each other out.

Theories as told by Physics students

What Happens When an unstoppable Force hits an immovable object?

Theory #1- In the case of an unstoppable force colliding with an immovable object, we must imagine that both objects are the same, both are unstoppable and both are immovable, nothing can stop them and nothing can move them, except for each other.

Theory #2- The Unstoppable force will pass straight through the immovable object, the unstoppable force remains unstoppable and the immovable object remains immovable.

Theory #3- The unstoppable force combines with the immovable object creating a black hole which is both unstoppable and immovable.

Theory #4- The unstoppable force will ricochet off the immovable object and the unstoppable force still has not been stopped, the immovable object has not been moved.

Theory #5- The only object known to man which is unstoppable is a black hole, it also can not be moved, except by another larger black hole. All types of radiation, light, gamma etc. are all absorbed by black holes. As an off topic question, is a black hole the universe Contracting? Scientist say they can still see the Universe Expanding at an accelerated rate, But that could have been a few billion years ago, as light is not instant and takes time to travel across the universe.