(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.

(relativity) The phenomenon in which two observers who start together with identical clocks, follow different timelines, and then rejoin can have different elapsed times on their clocks, especially if one travels at a relativistic speed.

(relativity) The clock paradox.

(topology) The non-intuitive fact that it is possible to turn a sphere inside out in a three-dimensional space with possible self-intersections but without creating any crease.

(economics) The proposition that technological progress that increases the efficiency with which a resource is used tends to increase (rather than decrease) the rate of consumption of that resource.

A paradox, related to probability, where the expected win for repeated play of a game is infinite, so it seems that a player should be willing to pay any price to take part.

A particular self-referential paradox relating to the number of words in a descriptive phrase.

Hempel's paradox

The paradox where, given the observation that certain English phrases unambiguously define real numbers while others do not, there is an infinitely long list of English phrases that unambiguously define real numbers, yet (using a similar technique to Cantor's diagonal argument) it is possible to generate another such phrase not in the list.

A paradox arising from the question of what constitutes evidence for a statement. Observing objects that are neither black nor ravens may formally increase the likelihood that all ravens are black, even though, intuitively, these observations are unrelated.