Nothing comes from nothing (Latin: ex nihilo nihil fit) is a philosophical expression of a thesis first argued by Parmenides. It is associated with ancient Greek cosmology, such as presented not just in the opus of Homer and Hesiod, but also in virtually every philosophical system – there is no time interval in which a world didn't exist, since it couldn't be created ex nihilo in the first place. Note that Greeks also believed that things cannot disappear into nothing, just as they can't be created from nothing, but if they ceased to exist, they transform into some other form of being. We can trace this idea to the teaching of Empedocles. Today the idea is loosely associated with the laws of conservation of mass and energy.