From the composition of the universe to why giraffes have such long necks these are 25 unsolved scientific mysteries that will leave you scratching your head.
#15. What is the universe made of?
Atoms, the building blocks of everything around us, only account for 5% of the total matter in the universe. The other 95% has come to be called dark matter and dark energy. Apart from giving the mystery matter a name, though, not much is known about it.