String theory and the concept of a multiverse do not provide a definitive plan or design for our universe, nor do they offer an explanation for who or what might have designed such a system. These ideas are part of speculative theories and hypotheses in theoretical physics and cosmology, and they explore possibilities based on mathematical models and theoretical frameworks.
In string theory, the fundamental building blocks of the universe are tiny vibrating strings or higher-dimensional branes. These entities give rise to different particles and forces observed in our universe. String theory also suggests the existence of additional compact dimensions beyond the three spatial dimensions we are familiar with.
Regarding the multiverse concept, it arises from various theories and cosmological models, such as inflationary cosmology and certain interpretations of quantum mechanics. The idea is that our universe may be part of a larger ensemble of universes, each with different properties and physical laws.
However, it is important to note that these concepts are still speculative and not yet empirically confirmed. String theory is an active area of research, but it has not yet produced testable predictions that can be verified through experimental or observational data. Similarly, the existence of a multiverse is a topic of ongoing debate and investigation, with various proposals but limited empirical evidence.
As for the question of who or what designed such a system, that falls into the realm of metaphysics and philosophy, rather than empirical scientific inquiry. It is beyond the scope of science to provide answers to questions related to ultimate origins or the existence of a designer. The scientific method is primarily concerned with understanding the natural world through observation, experimentation, and the development of theories that can be tested and validated.
Questions about design, purpose, and ultimate origins are philosophical and theological in nature, and they lie outside the realm of scientific investigation. Different cultures, religions, and belief systems offer various explanations and interpretations regarding these matters.