Definition of "ylem" in Anglais

noun

1. (cosmology, now chiefly historical) In the Big Bang theory, the hot and dense plasma that made up the matter in the cosmos following the initial baryogenesis at an early stage of its expansion and cooling, from which the first atoms formed and photons decoupled. The emission of photons in this phase is regarded as the source of the cosmic microwave background.

   • Let us now consider the state of matter during the first minutes of the expansion process, when the temperature of the universe was many billions of degrees high. […] [T]he state of matter must be visualized as a hot gas formed entirely by nuclear particles; that is, protons, neutrons, and electrons. […] We will call this primordial mixture of nuclear particles "Ylem," [footnote: Pronounced: ī′lěm] reviving an obsolete noun which, according to Webster's Dictionary, means "the first substance from which the elements were supposed to be formed." Next we can ask what happened to the Ylem when its density and temperature began to drop as the result of the rapid expansion taking place in the young universe.