Cosmic microwave background measurements revealed extreme uniformity in temperature. Light could not have traveled far enough to equalize conditions across vast distances. This “horizon problem” challenged simple Big Bang models. Inflation solves this by rapidly stretching space so distant regions were once in causal contact. Studying this ensures our cosmological models accurately describe the universe.
It matters because uniformity tests the limits of cosmological theory.
It also guides refinements like inflation in explaining the early universe.
Distant parts of the universe look alike, even though they couldn’t have exchanged information.
Princeton University [princeton.edu]