Question

How has the expansion of the universe affected the cosmic microwave background radiation?

A. It has caused it to heat up.
B. It has caused it to cool.
C. It has caused it to blue shift.
D. It has caused it to red-shift.

Answer 1

The expansion of the universe has caused cosmic microwave background radiation to cool. As the universe expands, the radiation is stretched out, causing its wavelength to increase and its temperature to decrease. This phenomenon is known as cosmic microwave background radiation redshift.

the answer is D. It has caused it to red-shift.