What is the primary reason the CMB light observed today is in the microwave band rather than its original visible/infrared spectrum?

Answer

Cosmological redshift caused by the expansion of space

As space has stretched over nearly 13.8 billion years, the wavelength of the original light has also stretched drastically, shifting it from the visible/infrared range into the microwave band.

What is the primary reason the CMB light observed today is in the microwave band rather than its original visible/infrared spectrum?

#Videos

Cosmic Microwave Background Explained - YouTube

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