A physical paradox is an apparent contradiction relating to physical descriptions of the universe. As such, there are many different uses for the term ranging from a challenging thought experiment that seems to belie common sense to an actual breakdown of the mathematical theory that describes the physical universe. While many physical paradoxes have accepted resolutions that make them little more than curiosities, others may defy resolution and be the result of an inadequate interpretation of the theory, an assumption about the physical world that is violated, or an indication that the theory inadequately describes the conditions. In physics as in all of science, contradictions and paradoxes are generally assumed to be artifacts of error and incompleteness because reality is assumed to be completely consistent, although this is itself a philosophical assumption. When, as in fields such as quantum physics and relativity theory, existing assumptions about reality have been shown to break down, this has usually been dealt with by changing our understanding of reality to a new one which remains self-consistent in the presence of the new evidence.