* The Big Bang and Cosmic Expansion: The universe is indeed expanding, driven by the Big Bang. This expansion is measured by the redshift of distant galaxies, meaning light from them is stretched as the space between us and them expands.

* Gravity's Influence: However, within clusters of galaxies, gravity plays a significant role. The immense mass of galaxies within a cluster pulls them together, counteracting the outward expansion of space.

* Internal Motion: Galaxies within a cluster are not static. They move around each other, influenced by the gravitational pull of the entire cluster. This internal motion is separate from the overall expansion of the universe.

So, the answer is complex:

* On a large scale: The space between clusters of galaxies is expanding due to the Big Bang.

* Within a cluster: The expansion of space is slowed down and may even be overcome by the gravitational pull of the cluster's galaxies. Galaxies within the cluster move primarily due to their mutual gravitational interactions, not the expansion of space.

In summary: The expansion of the universe is happening everywhere, but within dense regions like galaxy clusters, gravity dominates the local dynamics.