The question of whether there is a limit to how big space can expand is still an open topic of scientific inquiry. Currently, our understanding suggests that space could continue to expand indefinitely, with no inherent limit to its size.
The expansion of the universe is influenced by a property called the cosmological constant or dark energy. Dark energy is a form of energy that is thought to permeate space and drive its expansion. The exact nature of dark energy is not well understood, but observations have indicated that it has a repulsive effect, causing the expansion of the universe to accelerate.
If dark energy remains constant or its influence persists, the expansion could continue indefinitely. In such a scenario, galaxies would move farther and farther apart, and the universe would become increasingly diffuse and less dense over vast timescales.
However, it's important to note that our understanding of the fundamental nature of the universe is still evolving. New observations and theoretical developments could potentially alter our current understanding of the expansion and its long-term behavior. Scientific research continues to explore these questions in cosmology and physics.
It's also worth mentioning that the concept of the "size" of the universe can be a bit nuanced. The observable universe, the part of the universe we can see due to the finite speed of light, is already vast, but there may be regions beyond our observational reach. Whether the universe extends infinitely or has a boundary is still a topic of investigation and speculation in cosmology.