In the concept of a multiverse, where multiple universes coexist, the notion of "space" between universes can be quite challenging to define precisely. The idea of space as we understand it within our own universe may not directly apply to the interplay between different universes in a multiverse scenario.
Different theories and models propose various concepts for how multiple universes could exist within a multiverse. Some theories suggest that these universes could be separated by vast distances, sometimes referred to as "branes" or "pocket universes," which exist in a higher-dimensional space. In this case, there could be empty space or other structures that separate these universes.
However, it's important to note that the nature of the multiverse is highly speculative, and the concept is not yet confirmed by empirical evidence. There are several different proposals and interpretations of the multiverse idea, such as inflationary multiverse, string theory landscape, or quantum multiverse, each with its own implications for the structure and interactions between universes.
In some versions of the multiverse, the universes could be disconnected and have no direct interaction with each other. In others, they might interact through fundamental forces or through the effects of gravity. The nature of these interactions, if they exist, and the properties of the space (if applicable) between universes are still subjects of active research and debate among physicists and cosmologists.
Overall, the concept of space between universes within a multiverse is a speculative and ongoing area of investigation, and our current understanding of the multiverse is limited. Future theoretical developments and observational evidence may shed more light on this fascinating topic.