What is "ylem"

n. (context physics astronomy cosmology now chiefly historical English) In the Big Bang theory, the hot and dense plasma of which the cosmos consisted at the time of recombination in an early stage of its expansion and cooling, when the first atoms formed and photons decoupled, the source of the cosmic background radiation.

n. (cosmology) the original matter that (according to the big bang theory) existed before the formation of the chemical elements

Ylem is a term that was used by George Gamow, Ralph Alpher, and their associates in the late 1940s for a hypothetical original substance or condensed state of matter, which became subatomic particles and elements as we understand them today. The term ylem was actually coined by Ralph Alpher.

In modern understanding, the "ylem" described as by Gamow was the primordial plasma, formed in baryogenesis, which underwent Big Bang nucleosynthesis and was opaque to radiation. Recombination of the charged plasma into neutral atoms made the Universe transparent at the age of 380,000 years, and the radiation released is still observable as cosmic microwave background radiation.

Ylem (pronounced e-lem) is the sixth full-length studio release from German melodic black metal band Dark Fortress; and the second to feature new vocalist Morean. The album was released on January 22, 2010 in Germany, Austria, Switzerland and on January 25, 2010 for the rest of Europe. It was also released on February 9, 2010 in the United States of America.

Ylem is a composition by Karlheinz Stockhausen for a variable ensemble of 19 or more players, and is given the work number 37 in his catalogue of compositions.