ylem

{{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}}{{Cite OED|term=ylem}} or {{IPAc-en|ˈ|aɪ|l|ə|m}}){{cite Merriam-Webster|ylem|access-date=2020-07-03}}{{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}} is a hypothetical original substance or condensed state of matter, which became subatomic particles and elements 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."The Cosmos--Voyage Through the Universe series, New York: 1988 Time-Life Books Page 75

In modern understanding, the "ylem" as described 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.

History

The term comes from an obsolete Middle English philosophical word that Alpher said he found in Webster's dictionary.{{Cite OED |term=ylem |id=231917 |date=2017}} 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{{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}}) and ultimately derives from the hūlē ({{langx|grc|ὕλη}}), probably through an accusative singular form in Latin hylen, hylem.{{Cite OED |term=hyle |id=90173 |date=2017}} In an oral history interview in 1968 Gamow talked about ylem as an old Hebrew word{{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}} (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 photons present. Alpher and Robert Herman made a scientific prediction in 1948 that we should still be able to observe these red-shifted photons today as an ambient cosmic microwave background radiation (CMBR) pervading all space with a temperature of about 5 kelvinsThe CosmosVoyage Through the Universe series, New York: 1988 Time-Life Books, Page 80. (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.

See also

References