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Resuscitation of Middle English ylem, one of several variants for the Medieval Latin hyle ‎(matter), a transliteration of Aristotle’s concept of “(fundamental) matter”, in Ancient Greek ὕλη ‎(húlē, wood(s), material(s), matter, subject) or πρώτη ὕλη (“fundamental matter”).

First known to have been used in modern English by George Gamow in a paper coauthored with Alpher and Bethe titled "The Origin of Chemical Elements", published in Physical Review, April 1st, 1948.

Note: Claimed to have been found by Robert Herman in a large dictionary. In an interview Gamow also associated ylem with a Hebrew word, which should have been ילם (substantive “blind”), similar in pronunciation and appropriate for the hypothetical darkness of ylem.


ylem ‎(uncountable)

  1. (physics, astronomy, cosmology, now chiefly historical) 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.
    • 1948, R. A. Alpher, Physical Review, volume LXXIV, page 1581:
      Very shortly after the beginning of the universal expansion, the ylem was a gas of neutrons only.
    • 1959, James Blish, A Clash of Cymbals (UK)/The Triumph of Time (USA), page 171:
      The ylem was the primordial flux of neutrons out of which all else emerged.


Usage notes[edit]

  • The word ylem reappeared in popular books on science, following the discovery (in 1964-5) of the predicted (in 1948) cosmic background radiation and publication of its images composed from measurements by satellites (COBE in 1992 and WMAP in 2003).


  • See below


Middle English[edit]


ylem (uncountable)

  1. Alternative form of yle
    • 1390, John Gower, Confessio Amantis, "Incipit Liber Septimus" [1], part 1, lines 214-222:
      For yit withouten eny fo rme
      Was that matiere universal,
      Which hihte Ylem in special.
      Of Ylem, as I am enformed,
      These elementz ben mad and formed,
      Of Ylem elementz they hote
      After the Scole of Aristote,
      Of whiche if more I schal reherce,
      Foure elementz ther ben diverse.