Irresistible force paradox

The Irresistible force paradox, also the unstoppable force paradox, is a classic paradox

Paradox

A paradox is a statement or group of statements that leads to a contradiction or a situation which defies intuition. The term is also used for an apparent contradiction that actually expresses a non-dual truth...

 formulated as "What happens when an irresistible force meets an immovable object?" This paradox is a form of the omnipotence paradox

Omnipotence paradox

The omnipotence paradox is a family of related paradoxes addressing the question of what is possible for an omnipotent being to do. The paradox states that if the being can perform such actions, then it can limit its own ability to perform actions and hence it cannot perform all actions, yet, on...

, 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, no force is completely irresistible, and there are no immovable objects and cannot be any, as even a minuscule force will cause a slight acceleration on an object of any mass. An immovable object would have to have an inertia

Inertia

Inertia is the resistance of any physical object, to a change in its state of motion. It is represented numerically by an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to describe the motion of matter and how it is affected by...

 that was infinite, and therefore infinite mass. Such an object would collapse under its own gravity and create a singularity

Gravitational singularity

A gravitational singularity or spacetime singularity is a location where the quantities that are used to measure the gravitational field become infinite in a way that does not depend on the coordinate system...

. An unstoppable force would require infinite energy, which does not exist in a finite universe.

From a semantic point of view, 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.

An example of this paradox in non-western thought can be found in the origin of the Chinese word for paradox . This term originates from a story (see the Kanbun

Kanbun

The Japanese word originally meant "Classical Chinese writings, Chinese classic texts, Classical Chinese literature". This evolved into a Japanese method of reading annotated Classical Chinese in translation. It came to be that much Japanese literature intended for Japanese readers was written in...

example) in the 3rd century BC

3rd century BC

The 3rd century BC started the first day of 300 BC and ended the last day of 201 BC. It is considered part of the Classical era, epoch, or historical period.-Overview:...

 philosophical book Han Feizi

Han Feizi (book)

The Han Feizi is a work written by Han Feizi at the end of the Warring States Period in China, detailing his political philosophy. It belongs to the Legalist school of thought....

. 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."