the relationship between the double slit experiment/string theory/superposition and the multiple universe theory

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I have a basic understanding of what is happening during the double slit experiment and what we know it entails, same deal with string theory and superposition in general. My question is how they justify the existence of a multiverse. Maybe there’s a super simple explanation and I’m just missing it, or maybe the multiverse theory is independent of that other stuff. Please help me understand

In: Physics

What you seen to be asking about is the Many Worlds interpretation of quantum mechanics, which is somewhat close to the sci-fi idea of a multiverse though with some differences.

The idea comes from the fact that when we measure quantum objects, they seem to somehow change in nature. Before the measurement they evolve smoothly like a wave, this is what causes the interference pattern in the double slit experiment, however when we measure them they appear to have a single definite position, not spread out like a wave is.

The most common explanation is that the wavefunction (the quantum mechanical thing which describes the state of a system) collapses upon measurement. It goes from being a spread out wave to a single spike. The problem is we don’t really know why this would happen, and we don’t know at what point in the process it actually does.

The Many Worlds interpretation rejects wavefunction collapse and considers what would happen if instead the wavefunction just continues to evolve like normal. This is where you need to bring in entanglement and superposition. When a particle is measured, it becomes entangled with what you used to measure it. The state of one depends on the state of the other. For example if you have an electron and a device which detects its spin, when you make a measurement the electron and the detector become entangled. The state of the system is now a superposition of two states, either the electron was spin up and the detector measured spin up, or it was spin down and the detector measured spin down.
Many worlds applies this principle all the way up to the scale of the universe. We all become entangled with the system when the measurement is made, and so the wave-function which describes the system of the whole universe becomes a superposition of the two possible results. These two possible results are both real and a part of the wavefunction of the universe, but they behave like different branches and evolve on their own. Many worlds says that every time any things interact with each other, the possible results of those interactions split into new branches of the universal wavefunction, into new worlds effectively.