(relativity) The clock paradox.

(astronomy) The observation that the night sky is mostly dark, yet, in a boundless universe of stars, every line of sight from the eye must eventually intercept the surface of a star.

(economics) The apparent paradox that a rent seeker wanting political favours can bribe politicians at a cost much lower than the value of the favour to the rent seeker.

plural of Klein paradox

(quantum mechanics) A surprising result of applying the Dirac equation to the problem of electron scattering from a potential barrier. In non-relativistic quantum mechanics, electron tunnelling into a barrier is observed, with exponential damping. However, if the potential is of the order of the electron mass, V∼mc², the barrier is nearly transparent; moreover, as the potential approaches infinity, the reflection diminishes and the electron is always transmitted.

The linguistic paradox that, if there are unnameable things, their existence cannot be indicated without naming them in some way.

(physics) The black hole information paradox.

Synonym of paradox of thrift

(game theory) The paradox whereby a combination of losing strategies (such as alternating between two games that each, played individually, would result in an overall loss) may give a winning strategy.

(probability theory) The counterintuitive observation that a random group of people needs to have only 23 members before there is a 50% chance of two of them having the same birthday.