PX158 - K3 - cosmic microwave background

in $1966$ , researchers found a microwave signal coming from all directions in the sky
theorists predicted a cosmic background from $380 000 y r s$ after the start of the universe, when it became transparent/optically thin
for the CMB, $z \approx 1000$ , $T \approx 3000 K$ , so the background would be a blackbody, the most perfect blackbody
at $z = 0$ , this signal has red shifted to microwave radiation with a blackbody spectrum at $T = 2.73 K$
this was evidence for the "big bang theory"