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{{Short description|Hypothetical original substance or state of matter}}
{{about|a hypothetical substance|the musical composition|Ylem (Stockhausen)|the musical album|Ylem (album)}}

'''Ylem''' ({{IPAc-en|ˈ|iː|l|ɛ|m}}<ref>{{Cite OED|term=ylem}}</ref> or {{IPAc-en|ˈ|aɪ|l|ə|m}})<ref>{{cite Merriam-Webster|ylem|access-date=2020-07-03}}</ref><ref>{{Cite dictionary |url=http://www.lexico.com/definition/ylem |archive-url=https://web.archive.org/web/20200704024758/https://www.lexico.com/definition/ylem |url-status=dead |archive-date=2020-07-04 |title=ylem |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> is a hypothetical original substance or condensed [[state of matter]], which became [[subatomic particles]] and [[chemical element|element]]s as are understood today. The term was used by [[George Gamow]], his student [[Ralph Alpher]], and their associates in the late 1940s, having resuscitated it from [[Middle English]] after Alpher found it in [[Webster's Second]] dictionary, where it was defined as "the first substance from which the elements were supposed to have been formed."<ref>''The Cosmos''--''Voyage Through the Universe'' series, New York: 1988 Time-Life Books Page 75</ref>

In modern understanding, the "ylem" as described by Gamow was the primordial [[Plasma (physics)|plasma]], formed in [[baryogenesis]], which underwent [[Big Bang nucleosynthesis]] and was opaque to radiation. [[Recombination (cosmology)|Recombination]] of the charged plasma into neutral [[atom]]s made the universe transparent at the age of 380,000 years, and the radiation released is still observable as [[cosmic microwave background radiation]].

==History==
The term comes from an obsolete [[Middle English]] philosophical word that Alpher said he found in Webster's dictionary.<ref>{{Cite OED |term=ylem |id=231917 |date=2017}}</ref> The word means something along the lines of "primordial substance from which all matter is formed" (that in ancient [[mythology]] of many different cultures was called the [[cosmic egg]]<ref>{{cite journal |last=Bernstein |first=Jeremy |title=Out of My Mind: The Birth of Modern Cosmology |journal=The American Scholar |volume=55 |issue=1 |year=1986 |pages=7–18 |jstor=41211280}}</ref>) and ultimately derives from the ''hūlē'' ({{langx|grc|ὕλη}}), probably through an accusative singular form in Latin ''hylen, hylem''.<ref>{{Cite OED |term=hyle |id=90173 |date=2017}}</ref> In an oral history interview in 1968 Gamow talked about ylem as an old Hebrew word<ref>{{cite interview |last=Gamow |first=George |url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4325 |title=Oral Histories - George Gamow |interviewer=Charles Weiner |publisher=[[American Institute of Physics]] |date=25 April 1968}}</ref> (possibly {{lang|he|היולי}} "primordial", from the same Greek root {{lang|grc|ὕλη}}).

The ylem is what Gamow and colleagues presumed to exist immediately after the Big Bang. Within the ylem, there were assumed to be a large number of high-energy [[photon]]s present. Alpher and [[Robert Herman]] made a [[scientific prediction]] in 1948 that we should still be able to observe these [[red-shift]]ed photons today as an ambient [[cosmic microwave background radiation]] (CMBR) pervading all space with a temperature of about 5 [[kelvin]]s<ref>''The Cosmos'' – ''Voyage Through the Universe'' series, New York: 1988 Time-Life Books, Page 80.</ref> (when the CMBR was actually first detected in 1965, its temperature was found to be 3 kelvins). It is now recognized that the CMBR originated at the transition from predominantly ionized hydrogen to non-ionized hydrogen at around 400,000 years after the Big Bang.

==In popular culture ==
After the term ''ylem'' was resuscitated by Alpher, it was used in the 1952 [[science fiction]] novel ''Jack of Eagles'' by [[James Blish]]. It was also used by [[John Brunner (novelist)|John Brunner]] in his 1959 short story "Round Trip", reprinted in the collection ''[[Not Before Time]]''. [[Keith Laumer]] in the novel ''Dinosaur Beach'' introduces the ylem field 1969.  The term is also used by British author [[Richard Calder (writer)|Richard Calder]] in the 1990s to describe the [[quantum mechanical]] state of the "quantum magic" in the girls/robots in his "Dead" trilogy (''[[Dead Girls (novel)|Dead Girls]]'', ''[[Dead Boys (novel)|Dead Boys]]'', ''Dead Things''). [[John C. Wright (author)|John C. Wright]] used the term in his debut novel ''[[The Golden Age (John C. Wright novel)#Book 1: The Golden Age|The Golden Age]]'' to describe a "pseudo-matter" that forms "temporary virtual particles". A German black metal band "Dark Fortress" also released an album titled "Ylem". Synaesthesia, a trance classic by The Thrillseekers, has an "Ylem" remix. The video game series [[Ultima (series)|Ultima]] uses "Ylem" as a Word of Power in its incantation and runic based spell casting system, its meaning being "matter".

In 1981, Trudy Myrrh Reagan formed an organization, "Ylem: Artists Using Science and Technology" (later written YLEM), in the [[San Francisco Bay Area]].<ref>{{Cite web|url=http://www.ylem.org/Membership/history.html|title=Brief history of YLEM|website=www.ylem.org|access-date=2019-09-25}}</ref>

It is also a usable word in the Official Scrabble Players Dictionary, Fifth edition.

Some [[Frank Zappa]] releases include the phrase "This is '''Z'''appa '''F'''amily '''A'''rchival '''M'''atter '''I'''n '''L'''iving '''Y'''lem" among their [[copyright notice]]s.

== See also ==
{{Wiktionary}}
* [[Apeiron (cosmology)]]
* [[Baryogenesis]]
* [[Big Bang nucleosynthesis]]
* [[Quark matter]]

==References==
{{Reflist}}

[[Category:Early scientific cosmologies]]
[[Category:Physical cosmology]]