If the sun is in space, why is space so dark?

We all have seen those cool pictures of space where the Sun is rising behind Earth, they make us feel very peaceful and serene until you stop and think “Wait, if the sun is out there, why is space dark?” Well my friend you just invoked Olbers' Paradox. 

Olbers' Paradox is a fancy way of saying that even though the night sky should be bright with the infinite number of stars including our Sun, it is in fact very very dark.  As it turns out the lack of light has little to do with light itself and more to do with the size of the universe.

There are two main explanations for this phenomenon. The first, is that the universe is still pretty young.  It is only 15 billion years old (Aww, just a baby),  and due to its young age there hasn't been enough time for light from all the stars to reach us. The second is that the universe is also constantly expanding, therefore the stars are moving away from Earth too! Since light has a constant speed it will take even longer for it to reach us. Additionally, as the light sources move away from us, the light stretches out and decreases its frequency. The light changes from visible light to infrared, infrared to microwave, and microwave to radio wave. Unfortunately, this decrease in frequency means that it can’t be perceived with the naked eye and as a result we just see a dark sky.

Maybe one day when the universe is a little older light will reach us and we will see a very different sky when we look up! 

By Dr. Karen Ventura