We think that the universe is expanding because
A)the light from distant galaxies is very faint.
B)the light from distant galaxies is very bright.
C)distant galaxies are very small.
D)the light from distant galaxies is blueshifted.
E)the light from distant galaxies is redshifted.

Question

Quizplus · Accepted Answer

The most compelling evidence for an expanding universe is the observation that light from distant galaxies is redshifted. As these galaxies move away from us, the light they emit is stretched to longer, redder wavelengths. This means that their spectra show a shift towards longer wavelengths, which can be measured and used to calculate their recession velocities. The farther away a galaxy is, the faster it appears to be moving away from us, indicating that the universe as a whole is expanding.

We Think That the Universe Is Expanding Because