Eli5: If there's infinite stars, why isn't our night sky completely lit up?

There are not, as far as we know, infinite stars.

But - even if there were our observable universe is finite. There’s a phenomenon where space itself expands. This is, as far as we can tell, uniform. This means that two objects will see the amount of space between them continually increase at a rate that is proportional to their distance apart.

At a long enough distance (about 46 billion light years) the total expansion between the two objects results in the total space between them increasing faster than the speed of light. Once two objects are beyond this distance apart light from one cannot reach the other - the objects move outside each other’s observable universe.

So even if there were infinite stars outside that distance we couldn’t see them. We’re stuck with the stars and galaxies within the radius, which is a finite number, thus they emit a finite amount of light.

/r/explainlikeimfive Thread