The concept of "many-world interpretations" in quantum mechanics, such as the popular Many-Worlds Interpretation (MWI), is a theoretical proposal that attempts to explain the nature of quantum superpositions and the behavior of quantum systems at a macroscopic scale. MWI suggests that when a quantum system exists in a superposition of multiple states, rather than collapsing into a single state upon measurement, the universe branches into multiple parallel universes, each corresponding to one of the possible outcomes of the measurement.
To understand how quantum superpositions can lead to many-world interpretations, let's consider the famous thought experiment known as Schrödinger's cat. In this scenario, a cat is placed in a box along with a quantum system, such as a radioactive atom. The decay of the atom triggers a device that would release poison and lead to the cat's death. However, until the box is opened and the system is observed, according to quantum mechanics, the cat exists in a superposition of both alive and dead states.
According to the MWI, when the box is opened, the observer becomes entangled with the system. The observer's measurement interacts with the quantum superposition, causing the universe to branch into two distinct branches—one where the cat is observed as alive and another where the cat is observed as dead. These branches represent different outcomes of the measurement and exist as parallel universes, coexisting but independent of each other.
In this interpretation, the superposition of microscopic states extends to the macroscopic scale, leading to the idea that every quantum measurement creates new universes. The "many worlds" arise from the branching of the wave function, with each branch representing a different outcome. MWI suggests that there is no collapse of the wave function, but rather a continuous splitting of the universe into multiple parallel realities to accommodate all possible outcomes.
It's important to note that many-world interpretations, including MWI, are highly speculative and not universally accepted by all physicists. They serve as one way to interpret the mathematical formalism of quantum mechanics, but they are not currently supported by direct experimental evidence. Other interpretations, such as the Copenhagen interpretation, transactional interpretation, or hidden variable theories, provide alternative explanations for the behavior of quantum systems. The precise nature of quantum superpositions and the interpretation of quantum mechanics remain open questions in physics.