Which best describes cosmic microwave background radiation? radiation thought to exist but not yet measured radiation predicted to exist in millions of years radiation that existed before the big bang leftover radiation from the big bang

 leftover radiation from the big bang

Microwave background radiation is a form of electromagnetic radiation that is present in the whole universe and completely fills it.

Its frequency belongs to the microwaves range and is one of the main demonstrations of the of the Big Bang theory model.

It is important to note the Big Bang occurred 400,000 years before the events related to the microwave cosmic radiation, this means the Big Bang occurred first.

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