Many-world interpretations, such as the popular "Many-Worlds Interpretation" (MWI) of quantum mechanics, propose that quantum superpositions of microscopic states can lead to the existence of multiple parallel universes or "worlds" at a macroscopic scale. Here's a simplified explanation of how this interpretation works:
In quantum mechanics, superposition is a principle that allows particles or systems to exist in multiple states simultaneously. For example, an electron can be in a superposition of spin-up and spin-down states, meaning it is both spin-up and spin-down until measured or observed. MWI takes this idea further and suggests that instead of the superposition collapsing into a definite state upon measurement, all possible outcomes of a measurement actually occur, each in a separate universe.
According to MWI, when a measurement is made on a quantum system, the universe splits into multiple branches, with each branch corresponding to a different outcome of the measurement. For instance, if a particle's spin is measured, the universe branches into one branch where the particle's spin is measured as up and another branch where it is measured as down. Each branch represents a different possible outcome of the measurement, and these branches continue to evolve independently from that point onward.
MWI implies that there is no collapse of the wavefunction and no need for additional hidden variables or separate realities. Instead, it suggests that all the different outcomes exist simultaneously in separate branches of a vast multiverse, each following its own set of physical laws.
It is important to note that MWI is just one interpretation of quantum mechanics among several others, and its validity and testability remain subjects of debate among physicists. While MWI offers an intriguing way to explain the apparent randomness and measurement problem in quantum mechanics, it is still a speculative interpretation with philosophical implications that go beyond direct experimental verification.