These four worlds are spiritual, Heavenly realms in a descending chain, although the lowest world of Assiah has both a spiritual and a physical aspect. The physical level of Assiah is our physical finite realm, including the cosmological Universe studied by Science. Consequently, as Kabbalah is a metaphysical study, its reference to Ohr ("light") is a metaphor for Divine emanation, and the terms "higher" and "lower" are metaphors for closer and further from Divine consciousness and revelation.