The concept of a multiverse, which suggests the existence of multiple universes or regions with different properties, is a speculative idea that arises in certain theories in physics and cosmology. However, the nature of the space "in between" universes, if such a space exists, is highly speculative and not well understood. It's important to note that the idea of a multiverse is still a topic of ongoing research and debate, and there is no definitive experimental evidence for its existence.
Different theories propose various mechanisms for the existence of a multiverse, and they suggest different possibilities for what may occupy the space between universes, if anything. Here are a few concepts that have been proposed:
Bubble universes: In the context of inflationary cosmology, it is suggested that our universe is one among many bubble universes that arise through a process called eternal inflation. In this scenario, each bubble universe would be a separate entity with its own space and time. The space "between" these bubble universes could potentially be a region of rapidly expanding spacetime or a different kind of structure altogether.
Brane worlds: Some theories, such as string theory, propose the existence of additional spatial dimensions beyond the three dimensions we are familiar with. In these theories, our universe could be a brane (short for "membrane") embedded in a higher-dimensional space. The other branes could represent other universes or regions, and the space "in between" could be the higher-dimensional bulk where these branes exist.
Mathematical structures: Certain ideas in theoretical physics suggest that the multiverse could be described by mathematical structures or abstract concepts. In this view, the space "in between" universes might not have a physical existence but could be a manifestation of mathematical relationships or other fundamental principles.
It's important to emphasize that these are speculative ideas, and there is no consensus among physicists regarding the existence or nature of a multiverse or the space between universes, if they exist. The exploration of the multiverse concept is an active area of research, and future scientific advancements and theoretical developments may provide more insights into these questions.