View Full Version : When Was the First Light in the Universe?

2016-Nov-04, 11:01 PM
When was the first time that the Universe cooled down enough that light could finally move around?
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2016-Nov-05, 04:12 PM
I thought it was March 23, 1999. ;)

2016-Nov-07, 10:04 PM
Fraser. When the Big Bang plasma began to cool, the helium would have released light first. The ionization energy of the first electron in helium is almost twice that of hydrogen, and the ionization energy of the second electron being removed...is over 4 times that of neutral hydrogen. So, kind of like charging up a battery, if you spend the energy to charge it up, you ought to get most of it back as you discharge it.....(first law of thermodynamics)....and, as the temperature drops, the bare helium nucleus grabs the electrons while hotter than the hydrogen can, emitting line spectra from the edge of the plasma. I believe Sunyaev, and Chluba wrote a few papers on this circa 2009, and predicted a sensitive search should show it in WMAP, Planck data, though separating signal from noise might prove vexing. pete


SEE IONIZATION NRG Chart:https://en.wikipedia.org/wiki/Ionization_energies_of_the_elements_(data_page)