Why Is the Cosmic Microwave Background (CMB) So Cold If

question 47

Multiple Choice

Why is the cosmic microwave background (CMB) so cold if the early Universe was so hot

• A)Enough time has passed for matter in the universe to release enough heat to cool down.
• B)The CMB constantly interacts with atoms, which effectively cool down the photons.
• C)The expansion of the Universe has redshifted those photons to an effectively cooler temperature.
• D)Misleading; The big bang was initially hot but the CMB was released from cold material much later on.

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