Illustration & animation for Katie Mack’s monthly column in BBC Science Focus.

Dark Energy, which can safely be called the most mysterious phenomenon in our universe, has never been seen at all – it has evaded every attempt we’ve made to image or capture it with even our most advanced telescopes and sophisticated detector experiments. As far as we can tell, dark energy is something that is completely invisible, perfectly uniform throughout space, and has no interaction at all with matter or light. Its only function, through some as-yet undetermined mechanism, is to make space itself expand ever faster.