The concept of multiple universes or a multiverse is a speculative idea in physics and cosmology that suggests the existence of multiple universes, each with its own set of physical laws and properties. The notion of a multiverse is often explored in the context of various theoretical models, such as string theory, inflationary cosmology, or quantum mechanics.
In the context of a multiverse, it's important to understand that each universe within the multiverse can have its own distinct characteristics, including its size and whether it is finite or infinite. Some universes within a multiverse may indeed be infinite, while others may be finite.
When we talk about the "universe" in the context of cosmology, we generally refer to the observable universe—the portion of the entire universe that we can currently observe. The observable universe is finite because it has a finite age and is limited by the speed of light, which sets a boundary on the distance from which light has had time to reach us since the Big Bang.
However, it's worth noting that the concept of a multiverse is speculative, and we currently lack direct empirical evidence to confirm or refute its existence. The nature of the multiverse, including the properties and boundaries of its constituent universes, is still a topic of active research and debate among physicists and cosmologists. As our understanding of the universe evolves, so too may our understanding of the multiverse and its potential implications.