A mathematical explanation would involve a comparison of the density of stars throughout the universe with the inverse-square drop-off in light intensity from each.<p>If you assume for the sake of argument that all stars are as bright as the sun, and that stars have a uniform density throughout the universe (either a finite-but-huge or infinite universe, it makes little difference here), then you could solve for the mean intensity of light throughout, or in our case, &quot;how bright the sky is at night.&quot;<p>The article makes a classic (and really hard to escape! I&#x27;ve seen this sort of thing called a &quot;paradox&quot; on many occasions.) mistake of examining two infinite quantities (infinite stars, up to an infinite distance away) and assuming that they must cancel each other out, that infinity&#x2F;infinity=1. But not all infinities are the same, and infinity&#x2F;infinity can work out to 0, or to 0.1, or to pi, or to infinity (as in the case of &quot;# real numbers&quot;&#x2F;&quot;# integers&quot;), or to anything else; you have to look at the details -- what kind of infinity is it? -- and figure out how they compare.