Nothing, no-thing, or no thing, is the complete absence of anything; the opposite of everything, or its complement. The concept of nothing has been a matter of philosophical debate since at least the 5th century BC. Early Greek philosophers argued that it was impossible for nothing to exist. The atomists allowed nothing but only in the spaces between the invisibly small atoms. For them, all space was filled with atoms. Aristotle took the view that there exists matter and there exists space, a receptacle into which matter objects can be placed. This became the paradigm for classical scientists of the modern age like Newton. Nevertheless, some philosophers, like Descartes, continued to argue against the existence of empty space until the scientific discovery of a physical vacuum. Existentialists like Sartre and Heidegger (as interpreted by Sartre) have associated nothing with consciousness. Some writers have made connections between Heidegger's concept of nothing and the nirvana of Eastern religions. Modern science does not equate vacuum with nothing. Indeed, the vacuum in quantum field theory is filled with virtual particles. The quantum vacuum is often viewed as a modern version of an aether theory. Philosophy Western philosophy Some would consider the study of "nothing" to be absurd. A typical response of this type is voiced by Giacomo Casanova (1725–1798) in conversation with his landlord, one Dr. Gozzi, who also happens to be a priest: However, "nothingness" has been treated as a serious subject for a very long time. In philosophy, to avoid linguistic traps over the meaning of "nothing", a phrase such as not-being is often employed to make clear what is being discussed. Parmenides One of the earliest Western philosophers to consider nothing as a concept was Parmenides (5th century BC), who was a Greek philosopher of the monist school. He argued that "nothing" cannot exist by the following line of reasoning: To speak of a thing, one has to speak of a thing that exists. Since we can speak of a thing in the past, this thing must still exist (in some sense) now, and from this he concludes that there is no such thing as change. As a corollary, there can be no such things as coming-into-being, passing-out-of-being, or not-being. Other philosophers, for instance, Socrates and Plato. largely agreed with Parmenides's reasoning on nothing. Aristotle differs with Parmenides's conception of nothing and says, "Although these opinions seem to follow logically in