Cosmic background radiation

Question

How did the distribution of matter in the early universe affect how we are able to detect cosmic background radiation today?

Answer 1

At the beginning of the universe (about 13.8 billion years ago), the universe was in a hot, dense state, filled with a mix of plasma (electrons, protons, and photons) that interacted constantly. As the universe expanded and cooled, the temperature eventually dropped to about 3,000 K (around 380,000 years after the Big Bang), allowing protons and electrons to combine and form neutral hydrogen atoms. This process is called recombination.

Before recombination, photons (light) were constantly scattered by free electrons, preventing the universe from being transparent. After recombination, photons could travel freely through space because there were fewer free electrons to scatter them.

This released a sudden "burst" of radiation that we now observe as cosmic microwave background radiation (CMB). This radiation provides a snapshot of the universe after it became transparent.