Final answer:
The expansion of the universe is characterized by an increasing distance between galaxies, measured by the scale factor R, which suggests a uniform expansion over time. Recent observations indicate that this expansion may be accelerating, as distances are greater than expected when analyzing galactic redshifts.
Step-by-step explanation:
The expansion of the universe refers to the concept that the universe is not static but is, in fact, constantly expanding. This is represented by the change in the scale factor R, which is used to describe distances between galactic clusters. As R increases, the universe expands uniformly at the same rate everywhere.
One of the surprising recent findings is that this expansion may be accelerating, contrary to the initial expectation that it would slow down due to gravity. Researchers have utilized observations of supernovas to gather improved distance measurements, noticing that the distances are larger than what would be anticipated from the redshifts observed in galaxy light.
This suggests that the universe was expanding at a slower rate when this light was emitted. Current cosmological models and discussions, including those pertaining to dark matter, must account for these findings, which were first published in 1999, marking the commencement of a data-rich era in astronomy.