Baryon-to-Photon Ratio ·
η = n
b
/ n
γ
un
seel
.com · deuterium bottleneck · BBN · the CMB baryometer
η
6.1 × 10⁻¹⁰
photons / baryon
1.6 billion
Epoch
—
CMB photons (n
γ
)
Baryons: p + n
Deuterium / helium-4
Photodissociation
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.com · Baryon-to-Photon Ratio