The concept of what lies beyond the observable universe is speculative and uncertain. The observable universe is defined as the portion of the universe from which light has had enough time to reach us since the Big Bang, given the finite speed of light. It is estimated to have a radius of about 46.5 billion light-years.
However, the universe itself may be much larger than the observable universe. There are several possibilities for what might lie beyond our observable limit:
More of the same: One possibility is that the universe continues indefinitely beyond the observable universe, and its properties and structures persist on larger scales. This is known as the "infinite universe" or "eternal inflation" hypothesis. In this case, the observable universe would be just a tiny fraction of the entire cosmos.
Multiverse: Another possibility is that our universe is part of a larger "multiverse" that encompasses numerous separate regions, each with its own unique properties and physical laws. These regions, sometimes called "pocket universes" or "bubble universes," would be disconnected from each other and potentially have different laws of physics.
Cosmic Hierarchy: Some theories propose a cosmic hierarchy where our universe is part of a nested structure. It could be embedded within a higher-dimensional space or be one of many "branes" floating in a higher-dimensional "bulk." These ideas arise from certain interpretations of string theory and the concept of extra dimensions.
Unknown Physics: It's also possible that our current understanding of physics is incomplete, and there may be phenomena or structures beyond our current comprehension. Advancements in future scientific theories and technologies could reveal new aspects of the universe that we cannot currently fathom.
It's important to note that these ideas are speculative and theoretical, as direct observational evidence beyond the observable universe is currently beyond our reach. Exploring what lies beyond is an active area of research in cosmology and theoretical physics, and scientists are continually investigating and developing new theories and hypotheses to understand the nature of the universe on both observable and unobservable scales.