Galaxies and expanding space. Animation showing two spiral galaxies forming gravitational wells in the fabric of space-time, represented as a grid. The animation shows the grid expanding, representing the expansion of the universe. This is an expansion of space-time itself, with galaxies and other large-scale objects moving away from each other over time because of this underlying cosmological expansion. The animation zooms inwards from the largest to the smallest scale, showing the quantum foam (sometimes called space-time foam) that is thought to be the foundation of the fabric of the universe. Particles are being constantly created and destroyed at this level.