Irresistible force paradox

The irresistible force paradox, also called the unstoppable force paradox, shield and spear paradox, is a classic paradox formulated as "What happens when an unstoppable force meets an immovable object?" This paradox is a form of the omnipotence paradox, which is a simple demonstration that challenges omnipotence: "Can God create a stone so heavy that even God is not strong enough to lift it?" God, being almighty, should be able to create this stone, but if he does, he cannot move it, meaning that he is not almighty. However, if God cannot create this stone, the same problem arises. The immovable object and the irresistible force are both implicitly assumed to be indestructible, or else the question would have a trivial resolution. Furthermore, it is assumed that they are two separate entities.

The paradox arises because it rests on two incompatible premises: that there can exist simultaneously such things as irresistible forces and immovable objects. The "paradox" is flawed because if there exists an irresistible force, it follows logically that there cannot be any such thing as an immovable object and vice versa.[1]


An example of this paradox in non-western thought can be found in the origin of the Chinese word for contradiction (Chinese: 矛盾; pinyin: máodùn; literally: "Spear-Shield"). This term originates from a story (see the Kanbun example) in the 3rd century BC philosophical book Han Feizi.[2] 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". Another ancient and mythological example illustrating this theme can be found in the story of the Teumessian fox, who can never be caught, and the hound Laelaps, who never misses what it hunts. Realizing the paradox, Zeus turns both creatures into static stars.


The problems associated with this paradox can be applied to any other conflict between two abstractly defined extremes that are opposite.

One of the answers generated by seeming paradoxes like these is that there is no contradiction – that there is a false dilemma. Dr. Christopher Kaczor suggested that the need to change indicates a lack of power rather than the possession thereof, and as such a person who was omniscient would never need to change their mind – not changing the future would be consistent with omniscience rather than contradicting it.[3]

In the same way, an irresistible force, an object or force with infinite inertia, would be consistent with the definition of an immovable object, in that they would be one and the same. Any object whose momentum or motion cannot be changed is an immovable object, and it would halt any object that moved relative to it, making it an irresistible force.

Cultural references

In DC Comics All-Star Superman by Grant Morrison and Frank Quitely, Superman encounters a god-like figure from the 80th century, B.C., referred to as the Ultrasphinx. At some point in the past, when Samson and Atlas had stolen the Radioactive Crown Jewels of Atom-Hotep, the Ultrasphinx pursued them across time. Samson and Atlas knew they could not defeat the Ultrasphinx, and tricked Superman into helping them by gifting the jewels to Lois Lane. In the 21st century, the Ultrasphinx catches up to Samson, Atlas, and Superman, and, seeing Lois wearing the stolen jewels, places her in a state of quantum uncertainty, neither alive nor dead, stating "Return what was stolen and pay the price." Offering Superman an opportunity to free Lois from the state of quantum uncertainty, the Ultrasphinx then asks, "What happens when the unstoppable force meets the immovable object?" If answered correctly, Lane would be spared. If answered incorrectly, she would die. After considering the paradox, Superman then responds, "They surrender." After a brief moment of contemplation, Superman's response is accepted by the Ultrasphinx, and Lois is allowed to live. His judgment satisfied, the Ultrasphinx then returns to the past with the previously stolen Radioactive Crown Jewels of Atom-Hotep, having retrieved his prize and having been satisfactorily provided an acceptable answer to his seemingly paradoxical riddle. After a contest of strength that pits both Samson and Atlas against Superman in a simultaneous "two-on-one" arm wrestling match, Superman emerges as the victor and returns to his previous plans to celebrate Lois's birthday with her, including a voyage to the bottom of the ocean, and a trip to the moon, both of which are made possible by Lois's having been imbued with the same super powers as Superman for one day only.

See also


  1. Mike Alder (2004). "Newton's Flaming Laser Sword". Philosophy Now. 46: 29–33.
    Also available as Mike Alder (2004). "Newton's Flaming Laser Sword" (PDF). Mike Alder's Home Page. University of Western Australia. Archived from the original (PDF) on November 14, 2011.
  2. Han Feizi (韓非子), chapter 36, Nanyi (難一 "Collection of Difficulties, No. 1")'.
  3. Kaczor, Christopher (2009). This Rock, 20(3).
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