Why is space dark?
COSMOLOGY
The darkness of our night sky tells us more about the size, age and nature of the universe than we may expect. We are familiar with the twinkling of nearby stars in the night sky, but why does the night sky not glow with the colour and brightness of the average star? If the universe is infinite in size and age, then in every direction we look there should be a star or galaxy – well known to be powerful emitters of visible light. This puzzle is known as Olber’s paradox after 19th-century German astronomer Heinrich Olbers, and has attracted many attempts to resolve.
The first part in resolving this paradox is that the universe must have a finite age. This means only a finite number of stars can be observed from Earth in any direction, something which is true even if the universe itself has infinite size. The
