The term "multiverse" refers to the hypothetical concept of multiple universes or a collection of parallel, coexisting realities. It suggests the possibility that our universe is just one of many universes with potentially different physical laws, properties, or initial conditions.
Here are some distinctions between different types of universes often discussed in the context of the multiverse:
Parallel Universes: Parallel universes are closely related to the concept of the multiverse. They propose the existence of separate universes that exist alongside our own. These parallel universes could be similar to our universe, having the same fundamental laws of physics, but with different arrangements of matter and energy. The idea of parallel universes often arises from theories such as the Many-Worlds Interpretation of quantum mechanics or the concept of bubble universes in inflationary cosmology.
Alternative Universes: Alternative universes generally refer to potential versions or variations of our own universe. They are hypothetical scenarios that explore what the universe might have been like if certain events, conditions, or choices had been different. Alternative universes are often considered in the context of philosophical thought experiments or speculative fiction.
Shadow Universes: The term "shadow universe" is not commonly used in scientific discussions but is sometimes employed in works of fiction. In fictional contexts, a shadow universe typically refers to a parallel universe that mirrors our own but exists in a shadowy, distorted, or inverted form. These shadow universes often exhibit some level of connection or interaction with our own but may possess different rules or characteristics.
It's worth noting that these terms can sometimes be used interchangeably or have variations in meaning depending on the specific context or source. The concepts of parallel universes, alternative universes, and shadow universes all relate to the idea of multiple realities beyond our own, but they may differ in their underlying theoretical frameworks, characteristics, or implications.