Dark energy may be the most mysterious substance ever proposed, but many scientists are certain it exists. Why?

People have been asking why space is dark despite being filled with stars for so long that this question has a special name – Olbers’ paradox. Astronomers estimate that there are about 200 billion ...

A simple question with a profound answer: why is space dark? It's not about a lack of light; billions of stars flood the universe with it. The secret lies in the one thing Earth has that space doesn't ...