Cosmic neutrino background

The cosmic neutrino background (CNB or C $ν$ B^[a]) is the universe's background particle radiation composed of neutrinos. They are sometimes known as relic neutrinos.

The C $ν$ B is a relic of the Big Bang; while the cosmic microwave background radiation (CMB) dates from when the universe was 379,000 years old, the C $ν$ B decoupled (separated) from matter when the universe was just one second old. It is estimated that today, the C $ν$ B has a temperature of roughly 1.95 K.

As neutrinos rarely interact with matter, these neutrinos still exist today. They have a very low energy, around 10⁻⁴ to 10⁻⁶ eV.^[1]^[2] Even high energy neutrinos are notoriously difficult to detect, and the C $ν$ B has energies around 10¹⁰ times smaller, so the C $ν$ B may not be directly observed in detail for many years, if at all.^[1]^[2] However, Big Bang cosmology makes many predictions about the C $ν$ B, and there is very strong indirect evidence that the C $ν$ B exists.^[1]^[2]

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^ ^a ^b ^c ^d Cite error: The named reference Follin-Knox-Millea-Pan-2015 was invoked but never defined (see the help page).
^ ^a ^b ^c "Cosmic neutrinos detected, confirming the Big Bang's last great prediction". Forbes. Starts with a Bang. 9 September 2016.
Above is news coverage of the original academic paper:^[1]

[Follin-Knox-Millea-Pan-2015-2] Cite error: The named reference Follin-Knox-Millea-Pan-2015 was invoked but never defined (see the help page).

[Forbes-2016-09-09-cosmic-ν-3] "Cosmic neutrinos detected, confirming the Big Bang's last great prediction". Forbes. Starts with a Bang. 9 September 2016.
Above is news coverage of the original academic paper:^[1]

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