The Many-Worlds interpretation (MWI) of quantum mechanics is a theoretical framework that suggests the existence of multiple parallel universes, or "worlds," in which all possible outcomes of quantum events are realized. According to MWI, every quantum measurement leads to a branching of the universe, creating a separate reality for each possible outcome.
In the context of MWI, it is important to understand that the theory itself does not require or depend on the belief or acceptance of individuals. It is a proposed interpretation of quantum mechanics that attempts to explain the behavior of quantum systems. Whether or not people believe in MWI doesn't affect its validity as a theoretical framework.
Regarding the notion of a world where MWI is not true, it is indeed possible to conceive of such a scenario within the framework of MWI itself. MWI allows for the existence of different branches of reality, each following a different set of laws or principles. Therefore, there could hypothetically be a branch where MWI is not a valid description of reality.
However, it's important to note that MWI is an interpretation of quantum mechanics, and there are other interpretations as well, such as the Copenhagen interpretation or the pilot wave theory. These different interpretations offer alternative explanations for the behavior of quantum systems.
In the end, whether MWI or any other interpretation of quantum mechanics is true is still a subject of scientific investigation and debate. The existence of multiple interpretations highlights the complexity of understanding quantum phenomena fully.