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ylem
:''This article is about a hypothetical substance. For the musical composition of the same name, see Ylem (Stockhausen); for the musical album of the same name, see Ylem (album).''
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.〔''The Cosmos''--''Voyage Through the Universe'' series, New York:1988 Time-Life Books Page 75〕
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.
==History==
It reportedly comes from an obsolete Middle English philosophical word that Gamow's assistant Ralph Alpher came across while thumbing through a dictionary, which 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), and ultimately derives from the Greek ''ὕλη'' (''hūlē, hȳlē''), "matter," probably via an accusative singular form in Latin ''hylen, hylem''. Restated, the ylem is what Gamow, et al., presumed to exist immediately after the Big Bang. Within the ylem, there were assumed to be a large number of high-energy photons present. Ralph 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 five Kelvin〔''The Cosmos''--''Voyage 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 three Kelvin). 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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