The Expanding Universe (and Gravitational Equilibrium)

As distance between galaxies increases, their size does not. The space between galaxies or clusters of galaxies is growing in time. There is an increase in average distance between galaxies as the time progresses. As universe expands, the galaxies recede from one another.
Cosmological Principle: the Universe has neither a center nor an edge, which means matter is distributed uniformly throughout the universe on a very large scale.
Cosmological Theories: Maybe the Universe will be a re-collapsing universe, a critical universe, a coasting universe, or an accelerating universe.
The four universal forces are:

1. gravity,
2. electron,
3. strong force (holds atomic nuclei together),
4. weak force (mediates nuclear reactions)

Gravitational Equilibrium means a balance of gravitation vs. thermal pressure