Definitions for "YLEM"
the hypothetical primordial matter, proposed by George Gamow, from which the chemical elements may have been formed
(a) The word used by Gamow and his collaborators for the primordial material of the Big Bang. In most of his work Gamow assumed that the ylem consisted entirely of neutrons. In inflationary cosmology, the role of the ylem is played by the false vacuum. [G97] (b) Primordial state of matter - neutrons and their decay products (protons and electrons) - before the Big Bang. The term was taken from Aristotle and used for the -- theory. [A84
The original matter that (according to the big bang theory) existed before the formation of the chemical elements.