Your explanation is correct for individual stars, but it doesn&#x27;t take universal expansion into account, which independently reduces the energy available from distant sources (apart from the 1&#x2F;r^2 law). The reason? Same energy, more space, so a reduction in energy per unit of volume.<p>Also, setting aside the issue of expansion and redshift, if you imagine a sphere with a uniformly illuminated interior (imagine a surface composed of so many stars that counting them individually makes no sense) and an observation point at the center, if you increase the radius of the sphere, there&#x27;s no change in the energy received at the center.<p>This idea works for an infinite plane as well, and is a bit easier to grasp. Imagine an infinite plane with a fixed optical brightness, and an observation point at some distance d. Now double the distance -- no change in received energy because the plane is infinite in extent.