Reference articles on history, science, culture and more
Encyclopedia

Ylem

Hypothetical original substance or state of matter

Ylem (/ˈlɛm/ or /ˈləm/) 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."

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.

01History

The term comes from an obsolete Middle English philosophical word that Alpher said he found in Webster's dictionary. 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) and ultimately derives from the hūlē (Ancient Greek: ὕλη), probably through an accusative singular form in Latin hylen, hylem. In an oral history interview in 1968 Gamow talked about ylem as an old Hebrew word (possibly היולי "primordial", from the same Greek root 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 kelvins (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.

Watch videos about YlemExplainers and documentaries on YouTube (opens in a new tab)

Sources and credits

This article is adapted from the Wikipedia article Ylem, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

Fathomly is not affiliated with or endorsed by the Wikimedia Foundation. Spotted a problem? Tell us.