Brahman as the Universal Self is unchanging and eternal. "Brahman" is all that is eternal, unchanging and that which truly exists. It is, to an Advaitin, the unchanging, enduring, eternal absolute. Fixity implies repetition, rigidity and an unchanging order as well as disorder. In Buddhism process ontology is prevalent, seeing reality as empty of an unchanging essence. Physicists began changing the assumption that the Universe was static and unchanging. Parmenides thought that reality is timeless and unchanging. Things that once seemed static and unchanging become full of possibility and perfection. This seems to contradict the idea that stationary states should have unchanging properties. Parmenides' chief doctrine was that reality is a single unchanging and universal Being. The simplest propagating wave of unchanging form is a sine wave. Establishing oneself in the field of Being, or unchanging reality, ensures stability. Here, the use of the dative implies an unchanging situation. It need be neither unitary nor unchanging. The book challenged the then prevalent idea that caste was a rigid and unchanging institution.