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In Big Bang cosmology, neutrino decoupling was the epoch at which neutrinos ceased interacting with other types of matter, [1] and thereby ceased influencing the dynamics of the universe at early times. [2] Prior to decoupling, neutrinos were in thermal equilibrium with protons, neutrons and electrons, which was maintained through the weak ...
Another example is the neutrino decoupling which occurred within one second of the Big Bang. [4] Analogous to the decoupling of photons, neutrinos decoupled when the rate of weak interactions between neutrinos and other forms of matter dropped below the rate of expansion of the universe, which produced a cosmic neutrino background of freely streaming neutrinos.
At freeze out, the neutron–proton ratio was about 1/6. However, free neutrons are unstable with a mean life of 880 sec; some neutrons decayed in the next few minutes before fusing into any nucleus, so the ratio of total neutrons to protons after nucleosynthesis ends is about 1/7.
In other models, reheating is often considered to mark the start of the electroweak epoch, and some theories, such as warm inflation, avoid a reheating phase entirely. After inflation ended, the universe continued to expand, but at a decelerating rate. About 4 billion years ago the expansion gradually began to speed up again.
Decay from the 2s state by emitting two photons. This two-photon decay process is very slow, with a rate [9] of 8.22 s −1. It is however competitive with the slow rate of Lyman-α escape in producing ground-state hydrogen. Atoms in the first excited state may also be re-ionized by the ambient CMB photons before they reach the ground state ...
Because the rate of increase, n, is a constant average, the mean anomaly increases uniformly (linearly) from 0 to 2 π radians or 0° to 360° during each orbit. It is equal to 0 when the body is at the pericenter, π radians (180°) at the apocenter , and 2 π radians (360°) after one complete revolution. [ 4 ]
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The formula for this is: = (), where () is the proper distance at epoch , is the distance at the reference time , usually also referred to as comoving distance, and () is the scale factor. [3] Thus, by definition, d 0 = d ( t 0 ) {\displaystyle d_{0}=d(t_{0})} and a ( t 0 ) = 1 {\displaystyle a(t_{0})=1} .