Matter overtakes radiation
At 47,000 years, matter finally outweighs light — and structure can begin to grow.
- When
- Known to
- ± 20 million years
- Era
- Primordial
For its first tens of thousands of years the universe is dominated by radiation, whose pressure smooths out any clumping that tries to form. Around 47,000 years after the Big Bang, at a redshift near 3,400, the density of matter overtakes it. From this point gravity can amplify the faint density ripples left by inflation instead of having them washed out, which is the necessary precondition for every galaxy that follows.