Final answer:
Recent observations suggest that the universe's expansion is accelerating, likely due to dark energy, contrasted with the expected deceleration from gravitational forces.
Step-by-step explanation:
Recent observations have indicated that the rate of expansion of the universe is accelerating. This surprising phenomenon is contrary to the initial expectation that the mutual gravitational attraction between galaxies would slow down the expansion over time. Instead, a repulsive force, believed to be dark energy, is causing the expansion to speed up. The cosmological constant, introduced by Einstein, may counteract gravity's influence to facilitate this acceleration. The current Hubble constant, which measures this expansion rate, is approximately 22 kilometers per second per million light-years.
We are not at the center of this expansion, and it would appear uniform from any galaxy. Conceptually, this is understood as a stretching of space itself. With gravity alone, we would expect deceleration, but the acceleration observed suggests that there is far less visible matter than needed to halt expansion and that dark energy is playing a significant role in the dynamics of our universe's growth.