Which form of radiation is primarily associated with the early universe following the "Big Bang"?

The correct answer is cosmic microwave background radiation, as it is the remnant radiation from the early universe that fills the cosmos. This form of radiation is a crucial piece of evidence for the Big Bang theory, as it represents the radiation that was released when the universe cooled enough for electrons and protons to combine and form hydrogen atoms approximately 380,000 years after the Big Bang. This event allowed photons to travel freely, leading to the uniform microwave radiation we detect today.

Cosmic microwave background radiation is observed as a faint glow in every direction of the sky and has a thermal spectrum characteristic of a black body at around 2.7 Kelvin. This finding helps establish a timeline for the universe's evolution and supports models of cosmic expansion.

In contrast, infrared radiation, radio waves, and beta radiation are linked to different physical processes and phenomena. Infrared radiation is associated with thermal emissions from objects, radio waves are primarily linked with electromagnetic communication, and beta radiation involves the decay of radioactive materials, which does not relate directly to the conditions of the early universe following the Big Bang. Thus, the association of cosmic microwave background radiation with the early universe highlights its significance in astrophysics and cosmology.