Why sky seems dark at night?
Despite the glib answers, this is a profoundly hard question to answer. If the universe is infinite, the every direction you look there MUST be a star. So the sky should be bright. Even if there were dust and stuff in the way, the laws of physics say the dust would absorb the energy of the light, heat up and eventually re-readiate it – so if the universe is infinite then the night sky would still be bright. So, given the sky is dark at night, the question is actually “what happened to all the stars” or “is the universe really finite”. The answer comes in two parts. Firstly, the universe has not always been here. It started at the big bang. Whether space expanded to be infinite in the early universe or not, whichever way you look you cannot see any stars that are further away than light would have taken to get here since the big bang. Secondly, stars do not live forever. They collapse, die and go dark. So these two things mean that there are not an infinite number of stars that can be v
