Editing Many-worlds interpretation (section)

=== Testability ===

In 1985, [[David Deutsch]] proposed a variant of the [[Wigner's friend]] thought experiment as a test of many-worlds versus the Copenhagen interpretation.<ref name="deutsch1985">{{cite journal|last=Deutsch |first=D. |author-link=David Deutsch |year=1985 |title=Quantum theory as a universal physical theory |journal=[[International Journal of Theoretical Physics]] |volume=24 |number=1 |pages=1–41 |doi=10.1007/BF00670071 |bibcode=1985IJTP...24....1D|s2cid=17530632 }}</ref> It consists of an experimenter (Wigner's friend) making a measurement on a quantum system in an isolated laboratory, and another experimenter (Wigner) who would make a measurement on the first one. According to the many-worlds theory, the first experimenter would end up in a macroscopic superposition of seeing one result of the measurement in one branch, and another result in another branch. The second experimenter could then interfere these two branches in order to test whether it is in fact in a macroscopic superposition or has collapsed into a single branch, as predicted by the Copenhagen interpretation. Since then Lockwood, Vaidman, and others have made similar proposals,<ref name="vaidman_stanfordencyclopedia">{{cite book |last=Vaidman |first=Lev |title=Many-Worlds Interpretation of Quantum Mechanics |url=http://plato.stanford.edu/entries/qm-manyworlds/ |publisher=The Stanford Encyclopedia of Philosophy|year=2018 }}</ref> which require placing macroscopic objects in a coherent superposition and interfering them, a task currently beyond experimental capability.