The article makes no mistake, it just doesn't go into enough detail. To determine the amount of energy reaching us, we need to integrate over the energy densit

The article makes no mistake, it just doesn't go into enough detail. To determine the amount of energy reaching us, we need to integrate over the energy density divided by the square of the distance over the whole 3d space. As any physicist can tell you, an integral over the whole space will diverge unless the kernel falls off faster than 1/r^2. This means that one of the following must be true a) either the universe is finite, ie. the density falls off b) we don't integrate over the whole space (we can't see far enough due to age of universe) Which is exactly the argument this article is making Edit: in other words, infinite or finite-but-huge is an important difference when integrating over constant density; the former integral will diverge, the latter will not