I updated this post to be easier to access, and clarified some of the language.

In the Many Worlds interpretation, the universal quantum state is a giant superposition of all objects in the universe:

There is no ‘wave function’ collapse in this interpretation, so everything remains entangled. How then does this universe ‘split’? The usual story says that a measurement process yields several possibilities, much like the different possible sizes of the triangle below:

And it is these different possible outcomes that define how the universe splits into separate worlds, each corresponding to one of the outcomes:

But the problem is that in order to define a measurement process that yielded the clearly defined triangle outcomes, we assumed that there were distinguishable objects in our universe. Specifically, here’s what we needed in order to get those well-defined outcomes:

(1) a system that can have ‘triangle’ properties

(2) a large number of other, distinguishable systems that can measure those properties

(3) a clearly defined, force-based interaction…

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