a statement or proposition that, despite sound (or apparently sound) reasoning from acceptable premises, leads to a conclusion that seems senseless, logically unacceptable, or self-contradictory.
Catch-22: A situation in which someone is in need of something that can only be had by not being in need of it. A soldier who wants to be declared insane in order to avoid combat is deemed not insane for that very reason, and will therefore not be declared insane. Learn more.
Raven Paradox: Observing a green apple increases the likelihood of all ravens being black. Learn more.
Grand Hotel Paradox: If a hotel with infinitely many rooms is full, it can still take in more guests. Learn more.
Benardete’s Paradox: Apparently, a man can be “forced to stay where he is by the mere unfulfilled intentions of the gods”. Learn more.
Irresistible Force Paradox: What would happen if an unstoppable force hit an immovable object? Learn more.
Bootstrap Paradox: Can a time traveler send himself information with no outside source? Learn more.
Polchinski’s Paradox: A billiard ball can be thrown into a wormhole in such a way that it would emerge in the past and knock its incoming past self away from the wormhole entrance, creating a variant of the grandfather paradox. Learn more.
Predestination Paradox: A man travels back in time to discover the cause of a famous fire. While in the building where the fire started, he accidentally knocks over a kerosene lantern and causes a fire, the same fire that would inspire him, years later, to travel back in time. The bootstrap paradox is closely tied to this, in which, as a result of time travel, information or objects appear to have no beginning. Learn more.
Temporal Paradox: When did the ancestors of birds live? Learn more.
Grandfather Paradox: You travel back in time and kill your grandfather before he conceives one of your parents, which precludes your own conception and, therefore, you couldn’t go back in time and kill your grandfather. Learn more.
Hitler Paradox: You travel back in time and kill a famous person in history before they become famous; but if the person had never been famous then he could not have been targeted as a famous person. Learn more.
Hydrosatic Paradox: A massive battleship can float in a few litres of water. Learn more.
Problem of Evil: The existence of evil seems to be incompatible with the existence of an omnipotent, omniscient, and morally perfect God. Learn more.
Stability-instability Paradox: When two countries each have nuclear weapons, the probability of a direct war between them greatly decreases, but the probability of minor or indirect conflicts between them increases. Learn more.
Absence Paradox: No one is ever “here”. Learn more.
Ant On A Rubber Rope Paradox: An ant crawling on a rubber rope can reach the end even when the rope stretches much faster than the ant can crawl. Learn more.