Hugh Everett's many-worlds interpretation proposes that everything that could possibly have happened in our past, but did not, has occurred in the past of some other universe or universes and that every event has a branching action that could have been taken helps separates various worlds.

This view goes against the Copenhagen interpretation which views quantum mechanics not as objective reality, but rather predicts how measurements will affect the system. And by measuring the system a single path is chosen at random and all other options are collapsed.

Humorously, one of the things brought up by the Many-world's interpretation, Schrodinger's Cat was not developed to be taken seriously. Rather the inventor made it to remark on how strange quantum mechanics are.