The moment in which the dark is pierced by light, in the Universe, occurs 380,000 years after the Big Bang: here’s how – Guido Tonelli /Courier TV
The fourth day opens 380 thousand years after the “Big Bang” and the formation of protons and neutrons: a very long dark period in which the material universe aggregates, but there are still no structures capable of emitting light. When the expanding universe reaches a temperature of 3,000 degrees, photons stop being absorbed by a matter that was previously too dense. A reddish glow then crosses the entire universe: as written in the Bible, “there was light”. That background of cosmic radiation is still around us: a very precious source of information about the origin of the universe.