Radiation left over from the explosive birth of the universe, now in the microwave part of the spectrum, is known as what?

Radiation left over from the explosive birth of the universe, now in the microwave part of the spectrum, is known as what?

• A. Cosmic Microwave Background
• B. Visible Light
• C. Ultraviolet Radiation
• D. Infrared Background

Answer: (A)

Relic radiation from the Big Bang, now observed in microwaves, is the cosmic microwave background. It’s the afterglow left when the early universe cooled enough for photons to travel freely, about 380,000 years after the Big Bang. As the universe expanded, these photons stretched into longer wavelengths, shifting their peak into the microwave region. Today they form a nearly uniform background radiation at about 2.7 Kelvin across the sky. This makes it the best choice because it is precisely the leftover radiation from the universe’s birth that we now detect in the microwave part of the spectrum. Visible light is from stars, ultraviolet comes from very hot sources, and the infrared background mainly arises from dust and galaxies’ thermal emission rather than the original recombination glow.

Relic radiation from the Big Bang, now observed in microwaves, is the cosmic microwave background. It’s the afterglow left when the early universe cooled enough for photons to travel freely, about 380,000 years after the Big Bang. As the universe expanded, these photons stretched into longer wavelengths, shifting their peak into the microwave region. Today they form a nearly uniform background radiation at about 2.7 Kelvin across the sky. This makes it the best choice because it is precisely the leftover radiation from the universe’s birth that we now detect in the microwave part of the spectrum. Visible light is from stars, ultraviolet comes from very hot sources, and the infrared background mainly arises from dust and galaxies’ thermal emission rather than the original recombination glow.