Question

Why can't the spectrum of the CMB be explained as being the combined light of many stars and galaxies?

a) The CMB is too faint to be detected
b) The CMB has a unique blackbody spectrum that is distinct from star and galaxy spectra
c) The CMB is primarily composed of X-ray radiation
d) Stars and galaxies do not emit any radiation

Answer 1

The CMB's unique blackbody spectrum distinct from stars and galaxies and its uniformity across the sky, with a characteristic temperature of 2.725 K, provides evidence that it cannot be the combined light of many stars and galaxies. The correct answer is B

Step-by-step explanation:

The spectrum of the cosmic microwave background (CMB) cannot be explained as being the combined light of many stars and galaxies because the CMB has a unique blackbody spectrum that is distinct from star and galaxy spectra. This spectrum is characteristic of a temperature of 2.725 K, which is the cooled temperature of the Big Bang's remnant, and is incredibly uniform across the sky, unlike the varied spectra that would be expected from various individual celestial sources. Although the CMB is extremely smooth, it's not perfectly so; tiny fluctuations are present that correspond to the early seeds of structure in the universe which later evolved into stars and galaxies. The correct answer is B