I'd like to propose a thought experiment that in my opinion speaks for a many world interpretation.

Imagine Schrödingers Cat. Only we have a physicist in the box instead! Also inside the box is a photon emitter programmed to send a photon after 30 seconds. Our dear physicist has been instructed to, if he is still alive after 20 seconds (adjusted to have 50% prob) to move the emitter just a tiny little bit to the left. Now according to the quantum laws, the photon from the original position should create an interference pattern with the photon from the slightly moved position... provided we succeeded in creating a superposition of dead/alive physicist. Of course, every single experiment would just give one detection, so we would have to do it many times, to really verify that it worked.

The experiment could of course be scaled up, so that we instead proved that we had superpositions of planets being blown up or something. At some point, when the system in superposition is large enough - or significant enough -, I don't see how you could refrain from calling that many worlds.