One of the most fundamental discoveries about the universe has been that it is expanding. "The universe is expanding" means
A)our estimate for the size of the universe has increased over the last century.
B)galaxies are growing with time.
C)distances between most galaxies are getting larger.
D)the cosmological horizon is growing with time.

Question

Quizplus · Accepted Answer

The statement "the universe is expanding" refers to the fact that the distances between most galaxies are getting larger. This has been observed through the redshift of light from distant galaxies, which indicates that they are moving away from us (and from each other). The expansion of the universe does not refer to an increase in the size of the universe itself, nor does it mean that galaxies are growing with time. The cosmological horizon is a theoretical limit to our observable universe and is not directly affected by the expansion of the universe.

One of the Most Fundamental Discoveries About the Universe Has