Zeno’s paradoxes: “You will never reach point B from point A as you must always get half-way there, and half of the half, and half of that half, and so on …”
Omnipotence paradox: Can an omnipotent being create a rock too heavy for itself to lift?
Problem of evil: The existence of evil seems to be incompatible with the existence of an omnipotent, omniscient, and morally perfect God.
Bootstrap paradox: Can a time traveler send himself information with no outside source?
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.
Hitler’s murder 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.
Fermi paradox: If there are, as various arguments suggest, many other sentient species in the Universe, then where are they? Shouldn’t their presence be obvious?
Tea leaf paradox: When a cup of tea is stirred, the leaves assemble in the center, even though centrifugal force pushes them outward.
Upstream contamination: When a fluid is poured from a higher container onto a lower one, particles can climb up the falling water.
Irresistible force paradox: What would happen if an unstoppable force hit an immovable object?
Decision-making paradox: Selecting the best decision-making method is a decision problem in itself.
Fredkin’s paradox: The more similar two choices are, the more time a decision-making agent spends on deciding.
Liar paradox: “This sentence is false.” and “I’m lying.”
Card paradox: “The next statement is true. The previous statement is false.”
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.