Question

What is the cosmic background radiation? When and how did it form?

Short answer

The cosmic background radiation is the CMB, formed about 380,000 years after the Big Bang when the universe became transparent.

Step-by-step solution

Definition of Cosmic Background Radiation

The Cosmic Microwave Background (CMB) radiation is a form of electromagnetic radiation that fills the universe. It is the remnant radiation from the Big Bang and provides a snapshot of the early universe.

Formation of Cosmic Background Radiation

The CMB formed approximately 380,000 years after the Big Bang. At this time, the universe had cooled enough for protons and electrons to combine and form neutral hydrogen atoms, making the universe transparent to radiation.

Mechanism of Formation

During the era known as recombination, photons (light particles) could travel freely without being scattered by charged particles, marking the formation of the CMB. The universe, previously opaque due to charged plasma, became transparent.

Key concepts

Big Bang

The Big Bang is widely accepted as the event that led to the creation of our universe. It marks the beginning of time and space as we know it. Imagine a tiny point infinitely small and infinitely dense exploding. From this explosion, which occurred approximately 13.8 billion years ago, all matter, energy, space, and even time itself began to expand and cool.

The initial seconds following the Big Bang saw the formation of fundamental particles, like protons and neutrons. These particles eventually formed the first atomic nuclei during a period known as nucleosynthesis. Though it expanded rapidly, the universe was extremely hot and dense.
- Initiated the expansion and cooling down leading to galaxies, stars, and planets forming later.
- Created conditions suitable for chemical reactions that paved the way for life.

Recombination Era

The Recombination Era is a crucial phase in the history of the universe. Occurring around 380,000 years after the Big Bang, it was during this time that the universe cooled down enough for electrons to combine with protons to form neutral hydrogen atoms.

Before recombination, the universe was filled with a hot, dense plasma of charged particles. This opaque plasma scattered photons constantly, preventing light from traveling freely. As the universe cooled further, electrons were captured by protons, leading to the formation of neutral atoms.
- Allowed photons to travel unimpeded, leaving behind the Cosmic Microwave Background
- Marked the end of this hot dense plasma state, bringing about increased universe transparency.

Electromagnetic Radiation

Electromagnetic radiation encompasses a wide range of waves, including visible light, radio waves, X-rays, and microwaves. These waves travel at the speed of light and are a fundamental way in which energy is transferred across the universe.

The Cosmic Microwave Background is a form of electromagnetic radiation. Originally caused by the heat of the early universe, these microwaves are relics of the early explosion. They give us a glimpse into the universe's conditions during the early stages post-Big Bang.
- Consists of photons moving freely across space post-recombination
- Forms a crucial element in astronomical studies, helping us learn more about the fabric of the cosmos.

Universe Transparency

Universe Transparency signifies a major transformation in the history of the universe. Before the Recombination Era, the universe was a hot, dense soup of charged particles and scattered photons constantly. This made the universe opaque, much like a foggy day where visibility is limited.

With the formation of neutral atoms, light was able to travel without scattering. This transition is when the universe became 'transparent,' allowing radiation to move freely. It's this period that allowed the Cosmic Microwave Background to act as a calm and uniform glow permeating the universe.
- Enabled light and many forms of electromagnetic radiation to traverse through space
- Crucial for shaping our understanding of cosmological events and structures.