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Olbers' paradox is an observation regarding the darkness of the night sky, specifically, that if there were stars in every possible direction, something that could be imagined if the universe were infinitely large with an infinite number of randomly-distributed stars (and infinitely old so the light could reach us), the night sky would not be dark: it would all be bright. The fact that the night sky is dark is taken as evidence of limits on the size and/or age of the universe and/or the number of stars. And given other established astronomical facts, something must be changing, i.e., the universe must be dynamic in some way. The "paradox" is named for Heinrich Wilhelm Olbers, an early writer on the notion.