Why is the fact that the cosmic microwave background radiation is very smooth considered a problem?
A) A universe as smooth as predicted by the cosmic microwave background radiation should not have formed as many galaxies as have been observed.
B) A universe as smooth as predicted by the cosmic microwave background radiation should have collapsed by now.
C) A universe as smooth as predicted by the cosmic microwave background radiation should be expanding much faster than we are now.
D) A universe as smooth as predicted by the cosmic microwave background radiation should never have occurred occur because quantum mechanical fluctuations would have been imprinted on it.

Question

Quizplus · Accepted Answer

According to quantum mechanics, there should have been small fluctuations in the cosmic microwave background radiation. These fluctuations would have influenced the formation of structure in the universe, such as galaxies and stars. The fact that the cosmic microwave background radiation is very smooth, with only minor variations, is a problem because it contradicts this prediction. This is known as the "horizon problem" because it suggests that different regions of the universe that are now far apart were once close enough to interact and equalize their temperatures. However, if there were quantum fluctuations, these interactions would not have been able to occur over such great distances. Therefore, the smoothness of the cosmic microwave background radiation is considered a problem for the standard model of cosmology.

Why Is the Fact That the Cosmic Microwave Background Radiation